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  • 1.
    Alavaisha, Edmond
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography. University of Dar es Salaam, Tanzania.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Lindborg, Regina
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Different agricultural practices affect soil carbon, nitrogen and phosphorous in Kilombero -Tanzania2019In: Journal of Environmental Management, ISSN 0301-4797, E-ISSN 1095-8630, Vol. 234, p. 159-166Article in journal (Refereed)
    Abstract [en]

    Converting natural and semi-natural vegetation to agriculture is currently the most significant land use change at global scale. This conversion leads to changes in soil nutrients and increased CO2 emissions. However, knowledge of how soil organic carbon and nutrients change under various farming management is still limited, especially for small scale farming systems. This study evaluated the effects of different farming systems on soil organic carbon (SOC), total nitrogen (TN) and total phosphorous (TP) in subsistence farming at Kilombero, Tanzania. We applied an in-situ experimental setup, comparing maize and rice farming with and without irrigation and difference in fertilizers, with replicated soil sampling at five soil depths to a depth of 60 cm. The results show that irrigation had a positive effect on profile-averaged concentrations of SOC and TN, while fertilization had a positive effect on TN. Higher concentrations and stocks of TN were found in maize field soils compered to rice fields. In the vertical profile, irrigation and fertilization had positive effects on concentrations of SOC and TN of top soil layers, and the interaction between irrigation and fertilization extended the effect to deeper soil layers. Our results indicate that moderate irrigation and fertilization can help to improve carbon storage and nutrient availability (TN) in small-scale farming soils in Africa.

  • 2. Baker, Paul A.
    et al.
    Fritz, Sherilyn C.
    Dick, Christopher W.
    Eckert, Andrew J.
    Horton, Brian K.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Ribas, Camila C.
    Garzione, Carmala N.
    Battisti, David S.
    The emerging field of geogenomics: Constraining geological problems with genetic data2014In: Earth-Science Reviews, ISSN 0012-8252, E-ISSN 1872-6828, Vol. 135, p. 38-47Article in journal (Refereed)
    Abstract [en]

    The development of a genomics-derived discipline within geology is timely, as a result of major advances in acquiring and processing geologically relevant genetic data. This paper articulates the emerging field of geogenomics, which involves the use of large-scale genetic data to constrain geological hypotheses. The paper introduces geogenomics and discusses how hypotheses can be addressed through collaboration between geologists and evolutionary biologists. As an example, geogenomic methods are applied to evaluate competing hypotheses regarding the timing of the Andean uplift, the closure of the Isthmus of Panama, the onset of trans-Amazon drainage, and Quaternary climate variation in the Neotropics.

  • 3. Baskaran, Preetisri
    et al.
    Hyvönen, Riitta
    Berglund, S. Linnea
    Clemmensen, Karina E.
    Ågren, Göran I.
    Lindahl, Björn D.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Modelling the influence of ectomycorrhizal decomposition on plant nutrition and soil carbon sequestration in boreal forest ecosystems2017In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 213, no 3, p. 1452-1465Article in journal (Refereed)
    Abstract [en]

    Tree growth in boreal forests is limited by nitrogen (N) availability. Most boreal forest trees form symbiotic associations with ectomycorrhizal (ECM) fungi, which improve the uptake of inorganic N and also have the capacity to decompose soil organic matter (SOM) and to mobilize organic N (ECM decomposition'). To study the effects of ECM decomposition' on ecosystem carbon (C) and N balances, we performed a sensitivity analysis on a model of C and N flows between plants, SOM, saprotrophs, ECM fungi, and inorganic N stores. The analysis indicates that C and N balances were sensitive to model parameters regulating ECM biomass and decomposition. Under low N availability, the optimal C allocation to ECM fungi, above which the symbiosis switches from mutualism to parasitism, increases with increasing relative involvement of ECM fungi in SOM decomposition. Under low N conditions, increased ECM organic N mining promotes tree growth but decreases soil C storage, leading to a negative correlation between C stores above- and below-ground. The interplay between plant production and soil C storage is sensitive to the partitioning of decomposition between ECM fungi and saprotrophs. Better understanding of interactions between functional guilds of soil fungi may significantly improve predictions of ecosystem responses to environmental change.

  • 4. Beyer, Friderike
    et al.
    Jäck, Ortrud
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Weih, Martin
    Relationship between foliar δ13C and sapwood area indicates different water use patterns across 236 Salix genotypes2018In: Trees, ISSN 0931-1890, E-ISSN 1432-2285, Vol. 32, no 6, p. 1737-1750Article in journal (Refereed)
    Abstract [en]

    The relationship between leaf δ13C and plant size (represented by e.g. total leaf area) has been used to analyze different water use patterns of plants. However, the total leaf area (TLA) is difficult to assess in trees. Our aims were to (i) identify a feasible predictor for TLA; (ii) estimate the effects of TLA on leaf-level δ13C and δ18O values; and (iii) evaluate whether the relationship between leaf-level δ13C and a TLA proxy can be used to discriminate between different water use patterns. Various leaf and shoot traits of up to 236 Salix genotypes field-grown in Sweden and Italy were assessed and analyzed. Accumulated shoot diameter and sapwood area (SA) calculated from it were the best predictors for TLA. The SA was significantly correlated with foliar δ13C, but not δ18O values in some genotypes. The effects of SA on foliar δ13C values varied significantly among genotypes, and the foliar δ13C–SA relationship could be used to discriminate between different water use patterns across 236 Salix genotypes. Our results demonstrate a great variability of water use patterns across taxonomically closely related plants, and may also have implications for Salix pre-breeding and selection for different drought conditions.

  • 5. Brangari, Albert C.
    et al.
    Fernandez-Garcia, Daniel
    Sanchez-Vila, Xavier
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Ecological and soil hydraulic implications of microbial responses to stress - A modeling analysis2018In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 116, p. 178-194Article in journal (Refereed)
    Abstract [en]

    A better understanding of microbial dynamics in porous media may lead to improvements in the design and management of a number of technological applications, ranging from the degradation of contaminants to the optimization of agricultural systems. To this aim, there is a recognized need for predicting the proliferation of soil microbial biomass (often organized in biofilms) under different environments and stresses. We present a general multi-compartment model to account for physiological responses that have been extensively reported in the literature. The model is used as an explorative tool to elucidate the ecological and soil hydraulic consequences of microbial responses, including the production of extracellular polymeric substances (EPS), the induction of cells into dormancy, and the allocation and reuse of resources between biofilm compartments. The mechanistic model is equipped with indicators allowing the microorganisms to monitor environmental and biological factors and react according to the current stress pressures. The feedbacks of biofilm accumulation on the soil water retention are also described. Model runs simulating different degrees of substrate and water shortage show that adaptive responses to the intensity and type of stress provide a clear benefit to microbial colonies. Results also demonstrate that the model may effectively predict qualitative patterns in microbial dynamics supported by empirical evidence, thereby improving our understanding of the effects of pore-scale physiological mechanisms on the soil macroscale phenomena.

  • 6. Buendía, Corina
    et al.
    Kleidon, Axel
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Reu, Björn
    Porporato, Amilcare
    Evaluating the effect of nutrient redistribution by animals on the phosphorus cycle of lowland Amazonia2018In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 15, no 1, p. 279-295Article in journal (Refereed)
    Abstract [en]

    Phosphorus (P) availability decreases with soil age and potentially limits the productivity of ecosystems growing on old and weathered soils. Despite growing on ancient soils, ecosystems of lowland Amazonia are highly productive and are among the most biodiverse on Earth. P eroded and weathered in the Andes is transported by the rivers and deposited in floodplains of the lowland Amazon basin creating hotspots of P fertility. We hypothesize that animals feeding on vegetation and detritus in these hotspots may redistribute P to P-depleted areas, thus contributing to dissipate the P gradient across the landscape. Using a mathematical model, we show that animal-driven spatial redistribution of P from rivers to land and from seasonally flooded to terra firme (upland) ecosystems may sustain the P cycle of Amazonian lowlands. Our results show how P imported to land by terrestrial piscivores in combination with spatial redistribution of herbivores and detritivores can significantly enhance the P content in terra firme ecosystems, thereby highlighting the importance of food webs for the biogeochemical cycling of Amazonia.

  • 7. Capek, P. T.
    et al.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kastovska, E.
    Wild, B.
    Diakova, K.
    Barta, J.
    Schnecker, J.
    Blasi, C.
    Martikainen, P. J.
    Alves, R. J. E.
    Guggenberger, G.
    Gentsch, N.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Palmtag, Juri
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Mikutta, R.
    Shibistova, O.
    Urich, T.
    Schleper, C.
    Richter, A.
    Santruckova, H.
    A plant-microbe interaction framework explaining nutrient effects on primary production2018In: Nature Ecology & Evolution, E-ISSN 2397-334X, Vol. 2, no 10, p. 1588-1596Article in journal (Refereed)
    Abstract [en]

    In most terrestrial ecosystems, plant growth is limited by nitrogen and phosphorus. Adding either nutrient to soil usually affects primary production, but their effects can be positive or negative. Here we provide a general stoichiometric framework for interpreting these contrasting effects. First, we identify nitrogen and phosphorus limitations on plants and soil microorganisms using their respective nitrogen to phosphorus critical ratios. Second, we use these ratios to show how soil microorganisms mediate the response of primary production to limiting and non-limiting nutrient addition along a wide gradient of soil nutrient availability. Using a meta-analysis of 51 factorial nitrogen-phosphorus fertilization experiments conducted across multiple ecosystems, we demonstrate that the response of primary production to nitrogen and phosphorus additions is accurately predicted by our stoichiometric framework. The only pattern that could not be predicted by our original framework suggests that nitrogen has not only a structural function in growing organisms, but also a key role in promoting plant and microbial nutrient acquisition. We conclude that this stoichiometric framework offers the most parsimonious way to interpret contrasting and, until now, unresolved responses of primary production to nutrient addition in terrestrial ecosystems.

  • 8. Capek, Petr
    et al.
    Kotas, Petr
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Santruckova, Hana
    Drivers of phosphorus limitation across soil microbial communities2016In: Functional Ecology, ISSN 0269-8463, E-ISSN 1365-2435, Vol. 30, no 10, p. 1705-1713Article in journal (Refereed)
    Abstract [en]

    Nutrient limitation of soil microbial communities controls the rates of plant litter and soil organic matter decomposition and nutrient mineralization, and as such, it is central to soil and ecosystem models. According to ecological stoichiometry theory, when the carbon (C)-to-nutrient (E) ratio of resources used by a microbial community is higher than a critical ratio (C:E-CR), that nutrient is limiting. The C-to-phosphorus (P) critical ratio (C:P-CR) that determines P limitation is largely unknown for soils, and thus, it is the subject of our study. Our results show that the C:P-CR in widely different soils ranges from 26<bold></bold>6 to 465<bold></bold>1 or from 20<bold></bold>9 to 740<bold></bold>7 when accounting for 95% confidence intervals. Using constant or narrowly fluctuating C:P-CR in ecosystem models is therefore inaccurate. The C:P-CR cannot be simply predicted from microbial community C:P or available soil P. C:P-CR was only related to relative abundance of phospholipid fatty acids, which reflects microbial community structure and physiology. Our data suggest complex controls over microbial community C:P-CR. We further propose that using P storage compounds that allow the microbial community to temporarily buffer variability in available P can represent a widely adopted strategies across soils.

  • 9. Couvreur, Valentin
    et al.
    Ledder, Glenn
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Way, Danielle A.
    Muller, Erik B.
    Russo, Sabrina E.
    Water transport through tall trees: A vertically explicit, analytical model of xylem hydraulic conductance in stems2018In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 41, no 8, p. 1821-1839Article in journal (Refereed)
    Abstract [en]

    Trees grow by vertically extending their stems, so accurate stem hydraulic models are fundamental to understanding the hydraulic challenges faced by tall trees. Using a literature survey, we showed that many tree species exhibit continuous vertical variation in hydraulic traits. To examine the effects of this variation on hydraulic function, we developed a spatially explicit, analytical water transport model for stems. Our model allows Huber ratio, stem-saturated conductivity, pressure at 50% loss of conductivity, leaf area, and transpiration rate to vary continuously along the hydraulic path. Predictions from our model differ from a matric flux potential model parameterized with uniform traits. Analyses show that cavitation is a whole-stem emergent property resulting from non-linear pressure-conductivity feedbacks that, with gravity, cause impaired water transport to accumulate along the path. Because of the compounding effects of vertical trait variation on hydraulic function, growing proportionally more sapwood and building tapered xylem with height, as well as reducing xylem vulnerability only at branch tips while maintaining transport capacity at the stem base, can compensate for these effects. We therefore conclude that the adaptive significance of vertical variation in stem hydraulic traits is to allow trees to grow tall and tolerate operating near their hydraulic limits.

  • 10. D'Orangeville, Loic
    et al.
    Maxwell, Justin
    Kneeshaw, Daniel
    Pederson, Neil
    Duchesne, Louis
    Logan, Travis
    Houle, Daniel
    Arseneault, Dominique
    Beier, Colin M.
    Bishop, Daniel A.
    Druckenbrod, Daniel
    Fraver, Shawn
    Girard, Francois
    Halman, Joshua
    Hansen, Chris
    Hart, Justin L.
    Hartmann, Henrik
    Kaye, Margot
    Leblanc, David
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Ouimet, Rock
    Rayback, Shelly
    Rollinson, Christine R.
    Phillips, Richard P.
    Drought timing and local climate determine the sensitivity of eastern temperate forests to drought2018In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 24, no 6, p. 2339-2351Article in journal (Refereed)
    Abstract [en]

    Projected changes in temperature and drought regime are likely to reduce carbon (C) storage in forests, thereby amplifying rates of climate change. While such reductions are often presumed to be greatest in semi-arid forests that experience widespread tree mortality, the consequences of drought may also be important in temperate mesic forests of Eastern North America (ENA) if tree growth is significantly curtailed by drought. Investigations of the environmental conditions that determine drought sensitivity are critically needed to accurately predict ecosystem feedbacks to climate change. We matched site factors with the growth responses to drought of 10,753 trees across mesic forests of ENA, representing 24 species and 346 stands, to determine the broad-scale drivers of drought sensitivity for the dominant trees in ENA. Here we show that two factors-the timing of drought, and the atmospheric demand for water (i.e., local potential evapotranspiration; PET)-are stronger drivers of drought sensitivity than soil and stand characteristics. Droughtinduced reductions in tree growth were greatest when the droughts occurred during early-season peaks in radial growth, especially for trees growing in the warmest, driest regions (i.e., highest PET). Further, mean species trait values (rooting depth and psi(50)) were poor predictors of drought sensitivity, as intraspecific variation in sensitivity was equal to or greater than interspecific variation in 17 of 24 species. From a general circulation model ensemble, we find that future increases in earlyseason PET may exacerbate these effects, and potentially offset gains in C uptake and storage in ENA owing to other global change factors.

  • 11. Fatichi, Simone
    et al.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Or, Dani
    Paschalis, Athanasios
    A Mechanistic Model of Microbially Mediated Soil Biogeochemical Processes: A Reality Check2019In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 33, no 6, p. 620-648Article in journal (Refereed)
    Abstract [en]

    Present gaps in the representation of key soil biogeochemical processes such as the partitioning of soil organic carbon among functional components, microbial biomass and diversity, and the coupling of carbon and nutrient cycles present a challenge to improving the reliability of projected soil carbon dynamics. We introduce a new soil biogeochemistry module linked with a well-tested terrestrial biosphere model T&C. The module explicitly distinguishes functional soil organic carbon components. Extracellular enzymes and microbial pools are differentiated based on the functional roles of bacteria, saprotrophic, and mycorrhizal fungi. Soil macrofauna is also represented. The model resolves the cycles of nitrogen, phosphorus, and potassium. Model simulations for 20 sites compared favorably with global patterns of litter and soil stoichiometry, microbial and macrofaunal biomass relations with soil organic carbon, soil respiration, and nutrient mineralization rates. Long-term responses to bare fallow and nitrogen addition experiments were also in agreement with observations. Some discrepancies between predictions and observations are appreciable in the response to litter manipulation. Upon successful model reproduction of observed general trends, we assessed patterns associated with the carbon cycle that were challenging to address empirically. Despite large site-to-site variability, fine root, fungal, bacteria, and macrofaunal respiration account for 33%, 40%, 24%, and 3% on average of total belowground respiration, respectively. Simulated root exudation and carbon export to mycorrhizal fungi represent on average about 13% of plant net primary productivity. These results offer mechanistic and general estimates of microbial biomass and its contribution to respiration fluxes and to soil organic matter dynamics.

  • 12. Feng, Xue
    et al.
    Ackerly, David D.
    Dawson, Todd E.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    McLaughlin, Blair
    Skelton, Robert P.
    Vico, Giulia
    Weitz, Andrew P.
    Thompson, Sally E.
    Beyond isohydricity: The role of environmental variability in determining plant drought responses2019In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 42, no 4, p. 1104-1111Article in journal (Refereed)
    Abstract [en]

    Despite the appeal of the iso/anisohydric framework for classifying plant drought responses, recent studies have shown that such classifications can be strongly affected by a plant's environment. Here, we present measured in situ drought responses to demonstrate that apparent isohydricity can be conflated with environmental conditions that vary over space and time. In particular, we (a) use data from an oak species (Quercus douglasii) during the 2012-2015 extreme drought in California to demonstrate how temporal and spatial variability in the environment can influence plant water potential dynamics, masking the role of traits; (b) explain how these environmental variations might arise from climatic, topographic, and edaphic variability; (c) illustrate, through a common garden thought experiment, how existing trait-based or response-based isohydricity metrics can be confounded by these environmental variations, leading to Type-1 (false positive) and Type-2 (false negative) errors; and (d) advocate for the use of model-based approaches for formulating alternate classification schemes. Building on recent insights from greenhouse and vineyard studies, we offer additional evidence across multiple field sites to demonstrate the importance of spatial and temporal drivers of plants' apparent isohydricity. This evidence challenges the use of isohydricity indices, per se, to characterize plant water relations at the global scale.

  • 13. Feng, Xue
    et al.
    Ackerly, David D.
    Dawson, Todd E.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Skelton, Rob P.
    Vico, Giulia
    Thompson, Sally E.
    The ecohydrological context of drought and classification of plant responses2018In: Ecology Letters, ISSN 1461-023X, E-ISSN 1461-0248, Vol. 21, no 11, p. 1723-1736Article in journal (Refereed)
    Abstract [en]

    Many recent studies on drought‐induced vegetation mortality have explored how plant functional traits, and classifications of such traits along axes of, for example, isohydry–anisohydry, might contribute to predicting drought survival and recovery. As these studies proliferate, the consistency and predictive value of such classifications need to be carefully examined. Here, we outline the basis for a systematic classification of plant drought responses that accounts for both environmental conditions and functional traits. We use non‐dimensional analysis to integrate plant traits and metrics of environmental variation into groups that can be associated with alternative drought stress pathways (hydraulic failure and carbon limitation), and demonstrate that these groupings predict physiological drought outcomes using both synthetic and measured data. In doing so, we aim to untangle some confounding effects of environment and trait variations that undermine current classification schemes, advocate for more careful treatment of the environmental context within which plants experience and respond to drought, and outline a pathway towards a general classification of drought vulnerability.

  • 14.
    Fischer, Benjamin M. C.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Frentress, Jay
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Cousins, Sara A. O.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Greger, Maria
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Smittenberg, Rienk H.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Lyon, Steve W.
    Stockholm University, Faculty of Science, Department of Physical Geography. The Nature Conservancy, United States.
    Mojito, Anyone? An Exploration of Low-Tech Plant Water Extraction Methods for Isotopic Analysis Using Locally-Sourced Materials2019In: Frontiers in Earth Science, ISSN 2296-6463, Vol. 7, article id 150Article in journal (Refereed)
    Abstract [en]

    The stable isotope composition of water (delta O-18 and delta H-2) is an increasingly utilized tool to distinguish between different pools of water along the soil-plant-atmosphere continuum (SPAC) and thus provides information on how plants use water. Clear bottlenecks for the ubiquitous application of isotopic analysis across the SPAC are the relatively high-energy and specialized materials required to extract water from plant materials. Could simple and cost-effective do-it-yourself MacGyver methods be sufficient for extracting plant water for isotopic analysis? This study develops a suite of novel techniques for plant water extraction and compares them to a standard research-grade water extraction method. Our results show that low-tech methods using locally-sourced materials can indeed extract plant water consistently and comparably to what is done with other state-of-the-art methods. Further, our findings show that other factors play a larger role than water extraction methods in achieving the desired accuracy and precision of stable isotope composition: (1) appropriate transport, (2) fast sample processing and (3) efficient workflows. These results are methodologically promising for the rapid expansion of isotopic investigations, especially for citizen science and/or school projects or in remote areas, where improved SPAC understanding could help manage water resources to fulfill agricultural and other competing water needs.

  • 15.
    Fischer, Benjamin M. C.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Morillas, Laura
    Garcia, Monica
    Johnson, Mark S.
    Lyon, Steve W.
    Stockholm University, Faculty of Science, Department of Physical Geography. The Nature Conservancy, USA.
    Improving agricultural water use efficiency with biochar - A synthesis of biochar effects on water storage and fluxes across scales2019In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 657, p. 853-862Article in journal (Refereed)
    Abstract [en]

    There is an urgent need to develop agricultural methods that balance water supply and demand while at the same time improve resilience to climate variability. A promising instrument to address this need is biochar - a charcoal made from pyrolyzed organic material. However, it is often unclear how, if at all, biochar improves soil water availability, plant water consumption rates and crop yields. To address this question, we synthesized literature-derived observational data and evaluated the effects of biochar on evapotranspiration using a minimal soil water balance model. Results from the model were interpreted in the Budyko framework to assess how climatic conditions mediate the impacts of biochar on water fluxes. Our analysis of literature-derived observational data showed that while biochar addition generally increases the soil water holding capacity, it can have variable impacts on soil water retention relative to control conditions. Our modelling demonstrated that biochar increases long-term evapotranspiration rates, and therefore plant water availability, by increasing soil water retention capacity - especially in water-limited regions. Biochar amendments generally increased crop yields (75% of the compiled studies) and, in several cases (35% of the compiled studies), biochar amendments simultaneously increased crop yield and water use efficiencies. Hence, while biochar amendments are promising, the potential for variable impact highlights the need for targeted research on how biochar affects the soil-plant-water cycle.

  • 16. Hoeber, Stefanie
    et al.
    Fransson, Petra
    Prieto-Ruiz, Ines
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Weih, Martin
    Two Salix Genotypes Differ in Productivity and Nitrogen Economy When Grown in Monoculture and Mixture2017In: Frontiers in Plant Science, ISSN 1664-462X, E-ISSN 1664-462X, Vol. 8, article id 231Article in journal (Refereed)
    Abstract [en]

    Individual plant species or genotypes often differ in their demand for nutrients; to compete in a community they must be able to acquire more nutrients (i.e., uptake efficiency) and/or use them more efficiently for biomass production than their competitors. These two mechanisms are often complementary, as there are inherent trade-offs between them. In a mixed-stand, species with contrasting nutrient use patterns interact and may use their resources to increase productivity in different ways. Under contrasting nutrient availabilities, the competitive advantages conferred by either strategy may also shift, so that the interaction between resource use strategy and resource availability ultimately determines the performance of individual genotypes in mixtures. The aim was to investigate growth and nitrogen (N) use efficiency of two willow (Salix) genotypes grown in monoculture and mixture in a fertilizer contrast. We explored the hypotheses that (1) the biomass production of at least one of the involved genotypes should be greater when grown in mixture as compared to the corresponding monoculture when nutrients are the most growth-limiting factor; and (2) the N economy of individual genotypes differs when grown in mixture compared to the corresponding monoculture. The genotypes 'Tora' (Salix schwerinii x S. viminalis) and 'Loden' (S. dasyclados), with contrasting phenology and functional traits, were grown from cuttings in a growth container experiment under two nutrient fertilization treatments (high and low) in mono-and mixed-culture for 17 weeks. Under low nutrient level, 'Tora' showed a higher biomass production (aboveground biomass, leaf area productivity) and N uptake efficiency in mixture than in monoculture, whereas 'Loden' showed the opposite pattern. In addition, 'Loden' showed higher leaf N productivity but lower N uptake efficiency than 'Tora.' The results demonstrated that the specific functional trait combinations of individual genotypes affect their response to mixture as compared to monoculture. Plants grown in mixture as opposed to monoculture may thus increase biomass and vary in their response of N use efficiency traits. However, young plants were investigated here, and as we cannot predict mixture response in mature stands, our results need to be validated at field scale.

  • 17. Homyak, P. M.
    et al.
    Blankinship, J. C.
    Slessarev, E.
    Schaeffer, S. M.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Schimel, J. P.
    Effects of altered dry-season length and plant inputs on soluble soil carbon2018In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 99, no 10, p. 2348-2362Article in journal (Refereed)
    Abstract [en]

    Soil moisture controls microbial activity and soil carbon cycling. Because microbial activity decreases as soils dry, decomposition of soil organic matter (SOM) is thought to decrease with increasing drought length. Yet, microbial biomass and a pool of water‐extractable organic carbon (WEOC) can increase as soils dry, perhaps implying microbes may continue to break down SOM even if drought stressed. Here, we test the hypothesis that WEOC increases as soils dry because exoenzymes continue to break down litter, while their products accumulate because they cannot diffuse to microbes. To test this hypothesis, we manipulated field plots by cutting off litter inputs and by irrigating and excluding precipitation inputs to extend or shorten the length of the dry season. We expected that the longer the soils would remain dry, the more WEOC would accumulate in the presence of litter, whereas shortening the length of the dry season, or cutting off litter inputs, would reduce WEOC accumulation. Lastly, we incubated grass roots in the laboratory and measured the concentration of reducing sugars and potential hydrolytic enzyme activities, strictly to understand the mechanisms whereby exoenzymes break down litter over the dry season. As expected, extending dry season length increased WEOC concentrations by 30% above the 108 μg C/g measured in untreated plots, whereas keeping soils moist prevented WEOC from accumulating. Contrary to our hypothesis, excluding plant litter inputs actually increased WEOC concentrations by 40% above the 105 μg C/g measured in plots with plants. Reducing sugars did not accumulate in dry senesced roots in our laboratory incubation. Potential rates of reducing sugar production by hydrolytic enzymes ranged from 0.7 to 10 μmol·g−1·h−1 and far exceeded the rates of reducing sugar accumulation (~0.001 μmol·g−1·h−1). Our observations do not support the hypothesis that exoenzymes continue to break down litter to produce WEOC in dry soils. Instead, we develop the argument that physical processes are more likely to govern short‐term WEOC dynamics via slaking of microaggregates that stabilize SOM and through WEOC redistribution when soils wet up, as well as through less understood effects of drought on the soil mineral matrix.

  • 18. Hunt, Allen G.
    et al.
    Stefano, Manzoni
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Networks on Networks: The physics of geobiology and geochemistry2015Book (Other academic)
    Abstract [en]

    This book presents research into the physical rules that can underlie the behaviour of biota, as well as the geochemistry of soil development. It addresses both nutrient and water transport limitations of processes from chemical weathering to vascular plant growth. It attempts to bring order to the question of the extent to which soils can facilitate plant growth, and what limitations on plant sizes, metabolism, occurrence and correlations can be formulated thereby.

  • 19.
    Jaramillo, Fernando
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography. Stockholm University, Faculty of Science, Stockholm Resilience Centre. Florida International University, USA.
    Licero, Lucia
    Åhlen, Imenne
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Alexandra Rodriguez-Rodriguez, Jenny
    Guittard, Alice
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hylin, Anna
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Bolanos, Jiner
    Jawitz, James
    Wdowinski, Shimon
    Martinez, Oscar
    Fernanda Espinosa, Luisa
    Effects of Hydroclimatic Change and Rehabilitation Activities on Salinity and Mangroves in the Cienaga Grande de Santa Marta, Colombia2018In: Wetlands (Wilmington, N.C.), ISSN 0277-5212, E-ISSN 1943-6246, Vol. 38, no 4, p. 755-767Article in journal (Refereed)
    Abstract [en]

    The Cienaga Grande de Santa Marta (CGSM), Colombia is possibly the wetland that has experienced the largest mangrove mortality on record due to modification of hydrologic connectivity and consequent hypersaline conditions. We used hydroclimatic, salinity and mangrove basal area data collected in five stations from 1993 to 2015 to study the relation between ongoing mangrove recovery, changes in salinity in the wetland and hydroclimatic changes in precipitation, potential evapotranspiration and freshwater inputs. We found that until 2015, the mangrove ecosystems in CGSM are in general terms in a path of recovery due to the combined effect of favorable hydroclimatic conditions and management operations to increase freshwater inputs into the wetland. We observed in three stations that the annual growth of mangrove basal area increased as pore water salinity decreased. Regarding surface water salinity, El Nino/Southern Oscillation explained most of the inter-annual variability in the wet season by regulating freshwater and in the dry season by regulating potential evaporation from the wetland. However, persistent channel reopening appeared to be the cause for the largest salinity decreases, whereas lack of persistent dredging slowed recovery in other areas. The monitoring of the mangrove-salinity-hydroclimate system must continue in order to increase its understanding and to avoid more recurring episodes of mangrove mortality.

  • 20.
    Livsey, John
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Katterer, Thomas
    Vico, Giulia
    Lyon, Steve W.
    Stockholm University, Faculty of Science, Department of Physical Geography. The Nature Conservancy, USA..
    Lindborg, Regina
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Scaini, Anna
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Da, Chau Thi
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Do alternative irrigation strategies for rice cultivation decrease water footprints at the cost of long-term soil health?2019In: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 14, no 7, article id 074011Article in journal (Refereed)
    Abstract [en]

    The availability of water is a growing concern for flooded rice production. As such, several water-saving irrigation practices have been developed to reduce water requirements. Alternate wetting and drying and mid-season drainage have been shown to potentially reduce water requirements while maintaining rice yields when compared to continuous flooding. With the removal of permanently anaerobic conditions during the growing season, water-saving irrigation can also reduce CO2 equivalent (CO2eq) emissions, helping reduce the impact of greenhouse gas (GHG) emissions. However, the long-term impact of water-saving irrigation on soil organic carbon (SOC)-used here as an indicator of soil health and fertility-has not been explored. We therefore conducted a meta-analysis to assess the effects of common water-saving irrigation practices (alternate wetting and drying and mid-season drainage) on (i) SOC, and (ii) GHG emissions. Despite an extensive literature search, only 12 studies were found containing data to constrain the soil C balance in both continuous flooding and water-saving irrigation plots, highlighting the still limited understanding of long-term impacts of water-saving irrigation on soil health and GHG emissions. Water-saving irrigation was found to reduce emissions of CH4 by 52.3% and increased those of CO2 by 44.8%. CO2eq emissions were thereby reduced by 18.6% but the soil-to-atmosphere carbon (C) flux increased by 25% when compared to continuous flooding. Water-saving irrigation was also found to have a negative effect on both SOC-reducing concentrations by 5.2%-and soil organic nitrogen-potentially depleting stocks by more than 100 kgN/ha per year. While negative effects of water-saving irrigation on rice yield may not be visible in short-term experiments, care should be taken when assessing the long-term sustainability of these irrigation practices because they can decrease soil fertility. Strategies need to be developed for assessing the more long-term effects of these irrigation practices by considering trade-offs between water savings and other ecosystem services.

  • 21.
    Maneas, Giorgos
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography. Navarino Environmental Observatory, Greece.
    Makopoulou, Eirini
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Bousbouras, Dimitris
    Berg, Håkan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Anthropogenic Changes in a Mediterranean Coastal Wetland during the Last CenturyThe Case of Gialova Lagoon, Messinia, Greece2019In: Water, ISSN 2073-4441, E-ISSN 2073-4441, Vol. 11, no 2, article id 350Article, review/survey (Refereed)
    Abstract [en]

    Human interventions during the last 70 years have altered the characteristics of the Gialova Lagoon, a coastal wetland that is part of a wider Natura 2000 site. In this study, we explore how human interventions and climate altered the wetland's hydrological conditions and habitats, leading to changing wetland functions over time. Our interpretations are based on a mixed methodological approach combining conceptual hydrologic models, analysis of aerial photographs, local knowledge, field observations, and GIS (Geographic Information System) analyses. The results show that the combined effects of human interventions and climate have led to increased salinity in the wetland over time. As a result, the fresh and brackish water marshes have gradually been turned into open water or replaced by halophytic vegetation with profound ecological implications. Furthermore, current human activities inside the Natura 2000 area and in the surrounding areas could further impact on the water quantity and quality in the wetland, and on its sensitive ecosystems. We suggest that a more holistic understanding of the broader socio-ecological system is needed to understand the dynamics of the wetland and to achieve sustainable long-term management and conservation strategies.

  • 22.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Integrating plant hydraulics and gas exchange along the drought-response trait spectrum2014In: Tree Physiology, ISSN 0829-318X, E-ISSN 1758-4469, Vol. 34, no 10, p. 1031-1034Article in journal (Refereed)
  • 23.
    Manzoni, Stefano
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Katul, G.
    Invariant soil water potential at zero microbial respiration explained by hydrological discontinuity in dry soils2014In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 41, no 20, p. 7151-7158Article in journal (Refereed)
    Abstract [en]

    Soil microbial respiration rates decrease with soil drying, ceasing below water potentials around -15MPa. A proposed mechanism for this pattern is that under dry conditions, microbes are substrate limited because solute diffusivity is halted due to breaking of water film continuity. However, pore connectivity estimated from hydraulic conductivity and solute diffusivity (at Darcy's scale) is typically interrupted at much less negative water potentials than microbial respiration (-0.1 to -1MPa). It is hypothesized here that the more negative respiration thresholds than at the Darcy's scale emerge because microbial activity is restricted to microscale soil patches that retain some hydrological connectivity even when it is lost at the macroscale. This hypothesis is explored using results from percolation theory and meta-analyses of respiration-water potential curves and hydrological percolation points. When reducing the spatial scale from macroscale to microscale, hydrological and respiration thresholds become consistent, supporting the proposed hypothesis.

  • 24.
    Manzoni, Stefano
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Swedish University of Agricultural Sciences, Sweden.
    Katul, Gabriel
    Porporato, Amilcare
    A dynamical system perspective on plant hydraulic failure2014In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 50, no 6, p. 5170-5183Article in journal (Refereed)
    Abstract [en]

    Photosynthesis is governed by leaf water status that depends on the difference between the rates of transpiration and water supply from the soil and through the plant xylem. When transpiration increases compared to water supply, the leaf water potential reaches a more negative equilibrium, leading to water stress. Both high atmospheric vapor pressure deficit and low soil moisture increase the water demand while decreasing the supply due to lowered soil-to-root conductance and xylem cavitation. Therefore, dry conditions may eventually reduce the leaf water potential to the point of collapsing the plant hydraulic system. This hydraulic failure is shown to correspond to a fold bifurcation where the environmental parameters (vapor pressure deficit and soil moisture) trigger the loss of a physiologically sustainable equilibrium. Using a minimal plant hydraulic model, coordination among plant hydraulic traits is shown to result in increased resilience to environmental stresses, thereby impeding hydraulic failure unless hydraulic traits deteriorate due to prolonged water shortage or other damages.

  • 25.
    Manzoni, Stefano
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Moyano, F.
    Kätterer, T.
    Schimel, J.
    Modeling coupled enzymatic and solute transport controls on decomposition in drying soils2016In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 95, p. 275-287Article in journal (Refereed)
    Abstract [en]

    Mechanistic descriptions of microbial processes are difficult to embed in ecosystem models because they require complex mathematical formulations. The interactions between microbes, soil carbon (C), and water availability are particularly complex, as they involve coupled physical (advection and diffusion in unsaturated media) and biochemical processes (enzymatic reactions, C uptake by microbes). Here we propose an approximated equation based on a quasi-equilibrium assumption that describes microbial uptake of soil C as a function of soil moisture and organic matter content during soil drying. The equation predicts that uptake depends on two terms, one dependent on soil organic C concentration and enzyme availability (analogous to a Michaelis-Menten equation) and one dependent on soil moisture via its effects on enzyme and solute mass transfer, and microbial uptake kinetics. Assuming that uptake is proportional to microbial respiration, model results are compared to measured respiration water potential curves. Using independently estimated parameter values (except for the calibrated microbial uptake efficiency), the theoretical model captures well the respiration decline during drying and provides an explanation of respiration pulses at rewetting. Thus, this simple formulation could be employed in ecosystem models as an alternative to empirical respiration-moisture response functions.

  • 26.
    Manzoni, Stefano
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Swedish University of Agricultural Sciences, Sweden.
    Schaeffer, S. M.
    Katul, G.
    Porporato, A.
    Schimel, J. P.
    A theoretical analysis of microbial eco-physiological and diffusion limitations to carbon cycling in drying soils2014In: Soil Biology and Biochemistry, ISSN 0038-0717, E-ISSN 1879-3428, Vol. 73, p. 69-83Article in journal (Refereed)
    Abstract [en]

    Soil microbes face highly variable moisture conditions that force them to develop adaptations to tolerate or avoid drought. Drought conditions also limit the supply of vital substrates by inhibiting diffusion in dry conditions. How these biological and physical factors affect carbon (C) cycling in soils is addressed here by means of a novel process-based model. The model accounts for different microbial response strategies, including different modes of osmoregulation, drought avoidance through dormancy, and extra-cellular enzyme production. Diffusion limitations induced by low moisture levels for both extracellular enzymes and solutes are also described and coupled to the biological responses. Alternative microbial life-history strategies, each encoded in a set of model parameters, are considered and their effects on C cycling assessed both in the long term (steady state ahalysis) and in the short term (transient analysis during soil drying and rewetting). Drought resistance achieved by active osmoregulation requiring large C investment is not useful in soils where growth in dry conditions is limited by C supply. In contrast, dormancy followed by rapid reactivation upon rewetting seems to be a better strategy in such conditions. Synthesizing more enzymes may also be advantageous because it causes larger accumulation of depolymerized products during dry periods that can be used upon rewetting. Based on key model parameters, a spectrum of life-history strategies thus emerges, providing a possible classification of microbial responses to drought.

  • 27.
    Manzoni, Stefano
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Vico, G.
    Thompson, S.
    Beyer, F.
    Weih, M.
    Contrasting leaf phenological strategies optimize carbon gain under droughts of different duration2015In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 84, p. 37-51Article in journal (Refereed)
    Abstract [en]

    In most ecosystems, plants face periods with limited water availability, during which stomatal conductance is reduced to maintain hydration. However, prolonged dry spells might require more drastic strategies to conserve water, such as drought-deciduousness. If drought-related changes in leaf area are adaptive, it can be hypothesized that leaf area is optimized to maximize the growing-season carbon (C) gain. Different phenological strategies during drought have been proposed: (i) leaf area index (L) declines when net photosynthetic rates (A(net)) reach zero to maintain a non-negative A(net); (ii) L adjusts to avoid water potentials with negative impacts on A(net); (iii) a constant leaf water potential is maintained (isohydric behavior); and (iv) leaf area remains unaltered (i.e., summer-evergreen leaf habit). However, whether these strategies are optimal in terms of growing season C gains has not been assessed. Here we consider these theories in a unified framework using the same set of equations to describe gas exchanges and water transport in the soil plant atmosphere continuum, and quantify the effect of the leaf phenological strategy on plant C gain over the entire growing season in different climates. Longer dry periods tend to favor drought-deciduous rather than summer-evergreen habit. Deciduous plants that allow leaf water potential to fluctuate (anisohydric) while preventing negative A(net) assimilate more carbon than deciduous plants with fixed leaf water potentials (isohydric). Increased rooting depth allows evergreens to more effectively compete with drought-deciduous species. Moreover, increasing leaf nitrogen concentrations and thus photosynthetic capacity can be an effective acclimation strategy when dry periods are relatively short.

  • 28.
    Manzoni, Stefano
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Swedish University of Agricultural Sciences, Sweden.
    Vico, Giulia
    Katul, Gabriel
    Palmroth, Sari
    Porporato, Amilcare
    Optimal plant water-use strategies under stochastic rainfall2014In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 50, no 7, p. 5379-5394Article in journal (Refereed)
    Abstract [en]

    Plant hydraulic traits have been conjectured to be coordinated, thereby providing plants with a balanced hydraulic system that protects them from cavitation while allowing an efficient transport of water necessary for photosynthesis. In particular, observations suggest correlations between the water potentials at which xylem cavitation impairs water movement and the one at stomatal closure, and between maximum xylem and stomatal conductances, begging the question as to whether such coordination emerges as an optimal water-use strategy under unpredictable rainfall. Here mean transpiration <E> is used as a proxy for long-term plant fitness and its variations as a function of the water potentials at 50% loss of stem conductivity due to cavitation and at 90% stomatal closure are explored. It is shown that coordination between these hydraulic traits is necessary to maximize <E>, with rainfall patterns altering the optimal range of trait values. In contrast, coordination between ecosystem-level conductances appears not necessary to maximize <E>. The optimal trait ranges are wider under drier than under mesic conditions, suggesting that in semiarid systems different water use strategies may be equally successful. Comparison with observations across species from a range of ecosystems confirms model predictions, indicating that the coordinated functioning of plant organs might indeed emerge from an optimal response to rainfall variability.

  • 29. Mencuccini, Maurizio
    et al.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Christoffersen, Bradley
    Modelling water fluxes in plants: from tissues to biosphere2019In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 222, no 3, p. 1207-1222Article, review/survey (Refereed)
    Abstract [en]

    Models of plant water fluxes have evolved from studies focussed on understanding the detailed structure and functioning of specific components of the soil-plant-atmosphere (SPA) continuum to architectures often incorporated inside eco-hydrological and terrestrial biosphere (TB) model schemes. We review here the historical evolution of this field, examine the basic structure of a simplified individual-based model of plant water transport, highlight selected applications for specific ecological problems and conclude by examining outstanding issues requiring further improvements in modelling vegetation water fluxes. We particularly emphasise issues related to the scaling from tissue-level traits to individual-based predictions of water transport, the representation of nonlinear and hysteretic behaviour in soil-xylem hydraulics and the need to incorporate knowledge of hydraulics within broader frameworks of plant ecological strategies and their consequences for predicting community demography and dynamics.

  • 30. Mencuccini, Maurizio
    et al.
    Rosa, Teresa
    Rowland, Lucy
    Choat, Brendan
    Cornelissen, Hans
    Jansen, Steven
    Kramer, Koen
    Lapenis, Andrei
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Niinemets, Ülo
    Reich, Peter
    Schrodt, Franziska
    Soudzilovskaia, Nadia
    Wright, Ian J.
    Martínez-Vilalta, Jordi
    Leaf economics and plant hydraulics drive leaf: wood area ratios2019In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137Article in journal (Refereed)
    Abstract [en]

    Biomass and area ratios between leaves, stems and roots regulate many physiological and ecological processes. The Huber value H-v (sapwood area/leaf area ratio) is central to plant water balance and drought responses. However, its coordination with key plant functional traits is poorly understood, and prevents developing trait-based prediction models. Based on theoretical arguments, we hypothesise that global patterns in H-v of terminal woody branches can be predicted from variables related to plant trait spectra, that is plant hydraulics and size and leaf economics. Using a global compilation of 1135 species-averaged H-v, we show that H-v varies over three orders of magnitude. Higher H-v are seen in short small-leaved low-specific leaf area (SLA) shrubs with low K-s in arid relative to tall large-leaved high-SLA trees with high K-s in moist environments. All traits depend on climate but climatic correlations are stronger for explanatory traits than H-v. Negative isometry is found between H-v and K-s, suggesting a compensation to maintain hydraulic supply to leaves across species. This work identifies the major global drivers of branch sapwood/leaf area ratios. Our approach based on widely available traits facilitates the development of accurate models of above-ground biomass allocation and helps predict vegetation responses to drought.

  • 31.
    Messori, Gabriele
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology . Uppsala University, Sweden.
    Ruiz-Pérez, Guiomar
    Stockholm University, Faculty of Science, Department of Meteorology . Swedish University of Agricultural Sciences (SLU), Sweden.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Vico, G.
    Climate drivers of the terrestrial carbon cycle variability in Europe2019In: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 14, no 6, article id 063001Article, review/survey (Refereed)
    Abstract [en]

    The terrestrial biosphere is a key component of the global carbon cycle and is heavily influenced by climate. Climate variability can be diagnosed through metrics ranging from individual environmental variables, to collections of variables, to the so-called climate modes of variability. Similarly, the impact of a given climate variation on the terrestrial carbon cycle can be described using several metrics, including vegetation indices, measures of ecosystem respiration and productivity and net biosphere-atmosphere fluxes. The wide range of temporal (from sub-daily to paleoclimatic) and spatial (from local to continental and global) scales involved requires a scale-dependent investigation of the interactions between the carbon cycle and climate. However, a comprehensive picture of the physical links and correlations between climate drivers and carbon cycle metrics at different scales remains elusive, framing the scope of this contribution. Here, we specifically explore how climate variability metrics (from single variables to complex indices) relate to the variability of the carbon cycle at sub-daily to interannual scales (i.e. excluding long-term trends). The focus is on the interactions most relevant to the European terrestrial carbon cycle. We underline the broad areas of agreement and disagreement in the literature, and conclude by outlining some existing knowledge gaps and by proposing avenues for improving our holistic understanding of the role of climate drivers in modulating the terrestrial carbon cycle.

  • 32. Porporato, A.
    et al.
    Feng, X.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Mau, Y.
    Parolari, A. J.
    Vico, G.
    Ecohydrological modeling in agroecosystems: Examples and challenges2015In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 51, no 7, p. 5081-5099Article, review/survey (Refereed)
    Abstract [en]

    Human societies are increasingly altering the water and biogeochemical cycles to both improve ecosystem productivity and reduce risks associated with the unpredictable variability of climatic drivers. These alterations, however, often cause large negative environmental consequences, raising the question as to how societies can ensure a sustainable use of natural resources for the future. Here we discuss how ecohydrological modeling may address these broad questions with special attention to agroecosystems. The challenges related to modeling the two-way interaction between society and environment are illustrated by means of a dynamical model in which soil and water quality supports the growth of human society but is also degraded by excessive pressure, leading to critical transitions and sustained societal growth-collapse cycles. We then focus on the coupled dynamics of soil water and solutes (nutrients or contaminants), emphasizing the modeling challenges, presented by the strong nonlinearities in the soil and plant system and the unpredictable hydroclimatic forcing, that need to be overcome to quantitatively analyze problems of soil water sustainability in both natural and agricultural ecosystems. We discuss applications of this framework to problems of irrigation, soil salinization, and fertilization and emphasize how optimal solutions for large-scale, long-term planning of soil and water resources in agroecosystems under uncertainty could be provided by methods from stochastic control, informed by physically and mathematically sound descriptions of ecohydrological and biogeochemical interactions.

  • 33. Sierra, C. A.
    et al.
    Müller, M.
    Metzler, H.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Trumbore, S. E.
    The muddle of ages, turnover, transit, and residence times in the carbon cycle2017In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 23, no 5, p. 1763-1773Article in journal (Refereed)
    Abstract [en]

    Comparisons among ecosystem models or ecosystem dynamics along environmental gradients commonly rely on metrics that integrate different processes into a useful diagnostic. Terms such as age, turnover, residence, and transit times are often used for this purpose; however, these terms are variably defined in the literature and in many cases, calculations ignore assumptions implicit in their formulas. The aim of this opinion piece was i) to make evident these discrepancies and the incorrect use of formulas, ii) highlight recent results that simplify calculations and may help to avoid confusion, and iii) propose the adoption of simple and less ambiguous terms.

  • 34.
    Thorslund, Josefin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Jarsjö, Jerker
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Jaramillo, Fernando
    Stockholm University, Faculty of Science, Department of Physical Geography. Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Jawitz, James W.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Basu, Nandita B.
    Chalov, Sergey R.
    Cohen, Matthew J.
    Creed, Irena F.
    Goldenberg, Romain
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hylin, Anna
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kalantari, Zahra
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Koussis, Antonis D.
    Lyon, Steve W.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Mazi, Katerina
    Mård, Johanna
    Persson, Klas
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Pietroń, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Prieto, Carmen
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Quin, Andrew
    Stockholm University, Faculty of Science, Department of Physical Geography.
    van Meter, Kimberly
    Destouni, Georgia
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Wetlands as large-scale nature-based solutions: Status and challenges for research, engineering and management2017In: Ecological Engineering: The Journal of Ecotechnology, ISSN 0925-8574, E-ISSN 1872-6992, Vol. 108, p. 489-497Article in journal (Refereed)
    Abstract [en]

    Wetlands are often considered as nature-based solutions that can provide a multitude of services of great social, economic and environmental value to humankind. Changes in land-use, water-use and climate can all impact wetland functions and services. These changes occur at scales extending well beyond the local scale of an individual wetland. However, in practical applications, engineering and management decisions usually focus on individual wetland projects and local site conditions. Here, we systematically investigate if and to what extent research has addressed the large-scale dynamics of landscape systems with multiple wetlands, hereafter referred to as wetlandscapes, which are likely to be relevant for understanding impacts of regional to global change. Although knowledge in many cases is still limited, evidence suggests that the aggregated effects of multiple wetlands in the landscape can differ considerably from the functions observed at individual wetland scales. This applies to provisioning of ecosystem services such as coastal protection, biodiversity support, groundwater level and soil moisture regulation, flood regulation and contaminant retention. We show that parallel and circular flow-paths, through which wetlands are interconnected in the landscape, may largely control such scale-function differences. We suggest ways forward for addressing the mismatch between the scales at which changes take place and the scale at which observations and implementation are currently made. These suggestions can help bridge gaps between researchers and engineers, which is critical for improving wetland function-effect predictability and management.

  • 35.
    Thurner, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Beer, Christian
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Crowther, Thomas
    Falster, Daniel
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Prokushkin, Anatoly
    Schulze, Ernst-Detlef
    Sapwood biomass carbon in northern boreal and temperate forests2019In: Global Ecology and Biogeography, ISSN 1466-822X, E-ISSN 1466-8238, Vol. 28, no 5, p. 640-660Article in journal (Refereed)
    Abstract [en]

    Aim Information on the amount of carbon stored in the living tissue of tree stems (sapwood) is crucial for carbon and water cycle applications. Here, we aim to investigate sapwood-to-stem proportions and differences therein between tree genera and derive a sapwood biomass map. Location Northern Hemisphere boreal and temperate forests. Time period 2010. Major taxa studied Twenty-five common tree genera. Methods First, we develop a theoretical framework to estimate sapwood biomass for a given stem biomass by applying relationships between sapwood cross-sectional area (CSA) and stem CSA and between stem CSA and stem biomass. These measurements are extracted from a biomass and allometry database (BAAD), an extensive literature review and our own studies. The established allometric relationships are applied to a remote sensing-based stem biomass product in order to derive a spatially continuous sapwood biomass map. The application of new products on the distribution of stand density and tree genera facilitates the synergy of satellite and forest inventory data. Results Sapwood-to-stem CSA relationships can be modelled with moderate to very high modelling efficiency for different genera. The total estimated sapwood biomass equals 12.87 +/- 6.56 petagrams of carbon (PgC) in boreal (mean carbon density: 1.13 +/- 0.58 kgC m(-2)) and 15.80 +/- 9.10 PgC in temperate (2.03 +/- 1.17 kgC m(-2)) forests. Spatial patterns of sapwood-to-stem biomass proportions are crucially driven by the distribution of genera (spanning from 20-30% in Larix to > 70% in Pinus and Betula forests). Main conclusions The presented sapwood biomass map will be the basis for large-scale estimates of plant respiration and transpiration. The enormous spatial differences in sapwood biomass proportions reveal the need to consider the functionally more important sapwood instead of the entire stem biomass in global carbon and water cycle studies. Alterations in tree species distribution, induced by forest management or climate change, can strongly affect the available sapwood biomass even if stem biomass remains unchanged.

  • 36. Vico, Giulia
    et al.
    Dralle, David
    Feng, Xue
    Thompson, Sally
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    How competitive is drought deciduousness in tropical forests? A combined eco-hydrological and eco-evolutionary approach2017In: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 12, no 6, article id 065006Article in journal (Refereed)
    Abstract [en]

    Drought-deciduous and evergreen species are both common in tropical forests, where there is the need to cope with water shortages during periodic dry spells and over the course of the dry season. Which phenological strategy is favored depends on the long-term balance of carbon costs and gains that leaf phenology imposes as a result of the alternation of wet and dry seasons and the unpredictability of rainfall events. This study integrates a stochastic eco-hydrological framework with key plant economy traits to derive the long-term average annual net carbon gain of trees exhibiting different phenological strategies in tropical forests. The average net carbon gain is used as a measure of fitness to assess which phenological strategies are more productive and more evolutionarily stable (i.e. not prone to invasion by species with a different strategy). The evergreen strategy results in a higher net carbon gain and more evolutionarily stable communities with increasing wet season lengths. Reductions in the length of the wet season or the total rainfall, as predicted under climate change scenarios, should promote a shift towards more drought-deciduous communities, with ensuing implications for ecosystem functioning.

  • 37. Vico, Giulia
    et al.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Nkurunziza, Libere
    Murphy, Kevin
    Weih, Martin
    Trade-offs between seed output and life span - a quantitative comparison of traits between annual and perennial congeneric species2016In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 209, no 1, p. 104-114Article in journal (Refereed)
    Abstract [en]

    Perennial plants allocate more resources belowground, thus sustaining important ecosystem services. Hence, shifting from annual to perennial crops has been advocated towards a more sustainable agriculture. Nevertheless, wild perennial species have lower seed production than selected annuals, raising the questions of whether there is a fundamental trade-off between reproductive effort and life span, and whether such trade-off can be overcome through selection. In order to address these questions and to isolate life span from phylogenetic and environmental factors, we conducted a meta-analysis encompassing c. 3000 congeneric annual/perennial pairs from 28 genera. This meta-analysis is complemented with a minimalist model of long-term productivity in perennial species. Perennials allocate more resources belowground and less to seeds than congeneric annuals, independently of selection history. However, existing perennial wheat and rice could achieve yields similar to annuals if they survived three years and each year doubled their biomass, as other perennial grasses do. Selected perennial crops maintain the large belowground allocation of wild perennials, and thus can provide desired regulatory ecosystem services. To match the seed yield of annuals, biomass production of perennial grains must be increased to amounts attained by some perennial grasses - if this goal can be met, perennial crops can provide a more sustainable alternative to annuals.

  • 38. Vico, Giulia
    et al.
    Thompson, Sally E.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Swedish University of Agricultural Sciences (SLU), Sweden .
    Molini, Annalisa
    Albertson, John D.
    Almeida-Cortez, Jarcilene S.
    Fay, Philip A.
    Feng, Xue
    Guswa, Andrew J.
    Liu, Hu
    Wilson, Tiffany G.
    Porporato, Amilcare
    Climatic, ecophysiological, and phenological controls on plant ecohydrological strategies in seasonally dry ecosystems2015In: Ecohydrology, ISSN 1936-0584, E-ISSN 1936-0592, Vol. 8, no 4, p. 660-681Article, review/survey (Refereed)
    Abstract [en]

    Large areas in the tropics and at mid-latitudes experience pronounced seasonality and inter-annual variability in rainfall and hence water availability. Despite the importance of these seasonally dry ecosystems (SDEs) for the global carbon cycling and in providing ecosystem services, a unifying ecohydrological framework to interpret the effects of climatic variability on SDEs is still lacking. A synthesis of existing data about plant functional adaptations in SDEs, covering some 400 species, shows that leaf phenological variations, rather than physiological traits, provide the dominant control on plant-water-carbon interactions. Motivated by this result, the combined implications of leaf phenology and climatic variability on plant water use strategies are here explored with a minimalist model of the coupled soil water and plant carbon balances. The analyses are extended to five locations with different hydroclimatic forcing, spanning seasonally dry tropical climates (without temperature seasonality) and Mediterranean climates (exhibiting out of phase seasonal patterns of rainfall and temperature). The most beneficial leaf phenology in terms of carbon uptake depends on the climatic regime: evergreen species are favoured by short dry seasons or access to persistent water stores, whereas high inter-annual variability of rainy season duration favours the coexistence of multiple drought-deciduous phenological strategies. We conclude that drought-deciduousness may provide a competitive advantage in face of predicted declines in rainfall totals, while reduced seasonality and access to deep water stores may favour evergreen species. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

  • 39. Vico, Giulia
    et al.
    Way, Danielle A.
    Hurry, Vaughan
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Can leaf net photosynthesis acclimate to rising and more variable temperatures?2019In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 42, no 6, p. 1913-1928Article in journal (Refereed)
    Abstract [en]

    Under future climates, leaf temperature (T-l) will be higher and more variable. This will affect plant carbon (C) balance because photosynthesis and respiration both respond to short-term (subdaily) fluctuations in T-l and acclimate in the longer term (days to months). This study asks the question: To what extent can the potential and speed of photosynthetic acclimation buffer leaf C gain from rising and increasing variable T-l? We quantified how increases in the mean and variability of growth temperature affect leaf performance (mean net CO2 assimilation rates, A(net); its variability; and time under near-optimal photosynthetic conditions), as mediated by thermal acclimation. To this aim, the probability distribution of A(net) was obtained by combining a probabilistic description of short- and long-term changes in T-l with data on A(net) responses to these changes, encompassing 75 genera and 111 species, including both C3 and C4 species. Our results show that (a) expected increases in T-l variability will decrease mean A(net) and increase its variability, whereas the effects of higher mean T-l depend on species and initial T-l, and (b) acclimation reduces the effects of leaf warming, maintaining A(net) at >80% of its maximum under most thermal regimes.

  • 40. Wang, Lixin
    et al.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Ravi, Sujith
    Riveros-Iregui, Diego
    Caylor, Kelly
    Dynamic interactions of ecohydrological and biogeochemical processes in water-limited systems2015In: Ecosphere, ISSN 2150-8925, E-ISSN 2150-8925, Vol. 6, no 8, article id 133Article in journal (Refereed)
    Abstract [en]

    Water is the essential reactant, catalyst, or medium for many biogeochemical reactions, thus playing an important role in the activation and deactivation of biogeochemical processes. The coupling between hydrological and biogeochemical processes is particularly evident in water-limited arid and semi-arid environments, but also in areas with strong seasonal precipitation patterns (e.g., Mediterranean) or in mesic systems during droughts. Moreover, this coupling is apparent at all levels in the ecosystems-from soil microbial cells to whole plants to landscapes. Identifying and quantifying the biogeochemical hot spots'' and hot moments'', the underlying hydrological drivers, and how disturbance-induced vegetation transitions affect the hydrological-biogeochemical interactions are challenging because of the inherent complexity of these interactions, thus requiring interdisciplinary approaches. At the same time, a holistic approach is essential to fully understand function and processes in water-limited ecosystems and to predict their responses to environmental change. This article examines some of the mechanisms responsible for microbial and vegetation responses to moisture inputs in water-limited ecosystems through a synthesis of existing literature. We begin with the initial observation of Birch effect in 1950s and examine our current understanding of the interactions among vegetation dynamics, hydrology, and biochemistry over the past 60 years. We also summarize the modeling advances in addressing these interactions. This paper focuses on three opportunities to advance coupled hydrological and biogeochemical research: (1) improved quantitative understanding of mechanisms linking hydrological and biogeochemical variations in drylands, (2) experimental and theoretical approaches that describe linkages between hydrology and biogeochemistry (particularly across scales), and (3) the use of these tools and insights to address critical dryland issues of societal relevance.

  • 41. Way, Danielle A.
    et al.
    Katul, Gabriel G.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Swedish University of Agricultural Sciences, Sweden.
    Vico, Giulia
    Increasing water use efficiency along the C-3 to C-4 evolutionary pathway: a stomatal optimization perspective2014In: Journal of Experimental Botany, ISSN 0022-0957, E-ISSN 1460-2431, Vol. 65, no 13, p. 3683-3693Article in journal (Refereed)
    Abstract [en]

    C-4 photosynthesis evolved independently numerous times, probably in response to declining atmospheric CO2 concentrations, but also to high temperatures and aridity, which enhance water losses through transpiration. Here, the environmental factors controlling stomatal behaviour of leaf-level carbon and water exchange were examined across the evolutionary continuum from C-3 to C-4 photosynthesis at current (400 mu mol mol(-1)) and low (280 mu mol mol(-1)) atmospheric CO2 conditions. To this aim, a stomatal optimization model was further developed to describe the evolutionary continuum from C-3 to C-4 species within a unified framework. Data on C-3, three categories of C-3-C-4 intermediates, and C-4 Flaveria species were used to parameterize the stomatal model, including parameters for the marginal water use efficiency and the efficiency of the CO2-concentrating mechanism (or C-4 pump); these two parameters are interpreted as traits reflecting the stomatal and photosynthetic adjustments during the C-3 to C-4 transformation. Neither the marginal water use efficiency nor the C-4 pump strength changed significantly from C-3 to early C-3-C-4 intermediate stages, but both traits significantly increased between early C-3-C-4 intermediates and the C-4-like intermediates with an operational C-4 cycle. At low CO2, net photosynthetic rates showed continuous increases from a C-3 state, across the intermediates and towards C-4 photosynthesis, but only C-4-like intermediates and C-4 species (with an operational C-4 cycle) had higher water use efficiencies than C-3 Flaveria. The results demonstrate that both the marginal water use efficiency and the C-4 pump strength increase in C-4 Flaveria to improve their photosynthesis and water use efficiency compared with C-3 species. These findings emphasize that the advantage of the early intermediate stages is predominantly carbon based, not water related.

  • 42. Zhang, Haicheng
    et al.
    Goll, Daniel S.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Ciais, Philippe
    Guenet, Bertrand
    Huang, Yuanyuan
    Modeling the effects of litter stoichiometry and soil mineral N availability on soil organic matter formation using CENTURY-CUE (v1.0)2018In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 11, no 12, p. 4779-4796Article in journal (Refereed)
    Abstract [en]

    Microbial decomposition of plant litter is a crucial process for the land carbon (C) cycle, as it directly controls the partitioning of litter C between CO2 released to the atmosphere versus the formation of new soil organic matter (SOM). Land surface models used to study the C cycle rarely considered flexibility in the decomposer C use efficiency (CUEd) defined by the fraction of decomposed litter C that is retained as SOM (as opposed to be respired). In this study, we adapted a conceptual formulation of CUEd based on assumption that litter decomposers optimally adjust their CUEd as a function of litter substrate C to nitrogen (N) stoichiometry to maximize their growth rates. This formulation was incorporated into the widely used CENTURY soil biogeochemical model and evaluated based on data from laboratory litter incubation experiments. Results indicated that the CENTURY model with new CUEd formulation was able to reproduce differences in respiration rate of litter with contrasting C: N ratios and under different levels of mineral N availability, whereas the default model with fixed CUEd could not. Using the model with flexible CUEd, we also illustrated that litter quality affected the long-term SOM formation. Litter with a small C: N ratio tended to form a larger SOM pool than litter with larger C: N ratios, as it could be more efficiently incorporated into SOM by microorganisms. This study provided a simple but effective formulation to quantify the effect of varying litter quality (N content) on SOM formation across temporal scales. Optimality theory appears to be suitable to predict complex processes of litter decomposition into soil C and to quantify how plant residues and manure can be harnessed to improve soil C sequestration for climate mitigation.

  • 43. Zhang, Quan
    et al.
    Ficklin, Darren L.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Wang, Lixin
    Way, Danielle
    Phillips, Richard P.
    Novick, Kimberly A.
    Response of ecosystem intrinsic water use efficiency and gross primary productivity to rising vapor pressure deficit2019In: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 14, no 7, article id 074023Article in journal (Refereed)
    Abstract [en]

    Elevated vapor pressure deficit (VPD) due to drought and warming is well-known to limit canopy stomatal and surface conductance, but the impacts of elevated VPD on ecosystem gross primary productivity (GPP) are less clear. The intrinsic water use efficiency (iWUE), defined as the ratio of carbon (C) assimilation to stomatal conductance, links vegetation C gain and water loss and is a key determinant of how GPP will respond to climate change. While it is well-established that rising atmospheric CO2 increases ecosystem iWUE, historic and future increases in VPD caused by climate change and drought are often neglected when considering trends in ecosystem iWUE. Here, we synthesize long-term observations of C and water fluxes from 28 North American FLUXNET sites, spanning eight vegetation types, to demonstrate that ecosystem iWUE increases consistently with rising VPD regardless of changes in soil moisture. Another way to interpret this result is that GPP decreases less than surface conductance with increasing VPD. We also project how rising VPD will impact iWUE into the future. Results vary substantially from one site to the next; in a majority of sites, future increases in VPD (RCP 8.5, highest emission scenario) are projected to increase iWUE by 5%-15% by 2050, and by 10%-35% by the end of the century. The increases in VPD owing to elevated global temperatures could be responsible for a 0.13% year(-1) increase in ecosystem iWUE in the future. Our results highlight the importance of considering VPD impacts on iWUE independently of CO2 impacts.

  • 44. Zhang, Quan
    et al.
    Katul, Gabriel G.
    Oren, Ram
    Daly, Edoardo
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Yang, Dawen
    The hysteresis response of soil CO2 concentration and soil respiration to soil temperature2015In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 120, no 8, p. 1605-1618Article in journal (Refereed)
    Abstract [en]

    Diurnal hysteresis between soil temperature (T-s) and both CO2 concentration ([CO2]) and soil respiration rate (R-s) were reported across different field experiments. However, the causes of these hysteresis patterns remain a subject of debate, with biotic and abiotic factors both invoked as explanations. To address these issues, a CO2 gas transport model is developed by combining a layer-wise mass conservation equation for subsurface gas phase CO2, Fickian diffusion for gas transfer, and a CO2 source term that depends on soil temperature, moisture, and photosynthetic rate. Using this model, a hierarchy of numerical experiments were employed to disentangle the causes of the hysteretic [CO2]-T-s and CO2 flux T-s (i.e., F-T-s) relations. Model results show that gas transport alone can introduce both [CO2]-T-s and F-T-s hystereses and also confirm prior findings that heat flow in soils lead to [CO2] and F being out of phase with T-s, thereby providing another reason for the occurrence of both hystereses. The area (A(hys)) of the [CO2]-T-s hysteresis near the surface increases, while the A(hys) of the R-s-T-s hysteresis decreases as soils become wetter. Moreover, a time-lagged carbon input from photosynthesis deformed the [CO2]-T-s and R-s-T-s patterns, causing a change in the loop direction from counterclockwise to clockwise with decreasing time lag. An asymmetric 8-shaped pattern emerged as the transition state between the two loop directions. Tracing the pattern and direction of the hysteretic [CO2]-T-s and R-s-T-s relations can provide new ways to fingerprint the effects of photosynthesis stimulation on soil microbial activity and detect time lags between rhizospheric respiration and photosynthesis.

  • 45. Zhang, Quan
    et al.
    Phillips, Richard P.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Scott, Russell L.
    Oishi, A. Christopher
    Finzi, Adrien
    Daly, Edoardo
    Vargas, Rodrigo
    Novick, Kimberly A.
    Changes in photosynthesis and soil moisture drive the seasonal soil respiration-temperature hysteresis relationship2018In: Agricultural and Forest Meteorology, ISSN 0168-1923, E-ISSN 1873-2240, Vol. 259, p. 184-195Article in journal (Refereed)
    Abstract [en]

    In nearly all large-scale terrestrial ecosystem models, soil respiration is represented as a function of soil temperature. However, the relationship between soil respiration and soil temperature is highly variable across sites and there is often a pronounced hysteresis in the soil respiration-temperature relationship over the course of the growing season. This phenomenon indicates the importance of biophysical factors beyond just temperature in controlling soil respiration. To identify the potential mechanisms of the seasonal soil respiration-temperature hysteresis, we developed a set of numerical models to demonstrate how photosynthesis, soil moisture, and soil temperature, alone and in combination, affect the hysteresis relationship. Then, we used a variant of the model informed by observations of soil respiration, soil temperature, photosynthesis, and soil moisture from multiple mesic and semi-arid ecosystems to quantify the frequency of hysteresis and identify its potential controls. We show that the hysteresis can result from the seasonal cycle of photosynthesis (which supplies carbon to rhizosphere respiration), and soil moisture (which limits heterotrophic respiration when too low or too high). Using field observations of soil respiration, we found evidence of seasonal hysteresis in 9 out of 15 site-years across 8 diverse biomes. Specifically, clockwise hysteresis occurred when photosynthesis preceded seasonal soil temperature and counterclockwise hysteresis occurred when photosynthesis lagged soil temperature. We found that across all sites, much of the respiration-temperature lag was explained by the decoupling of photosynthesis and temperature, highlighting the importance of recently assimilated carbon to soil respiration. An analysis of observations from 129 FLUXNET sites revealed that time lags between gross primary productivity (a proxy for canopy photosynthesis) and soil temperature were common phenomena, which would tend to drive counterclockwise hysteresis at low-latitude sites and clockwise hysteresis at high-latitude sites. Collectively, our results show that incorporating photosynthesis and soil moisture in the standard exponential soil respiration-temperature model (i.e., Q(10) model) improves the explanatory power of models at local scales.

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