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Contribution of seagrass plants to CO2 capture in a tropical seagrass meadow under experimental disturbance
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
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Number of Authors: 72017 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 12, no 7, article id e0181386Article in journal (Refereed) Published
Abstract [en]

Coastal vegetative habitats are known to be highly productive environments with a high ability to capture and store carbon. During disturbance this important function could be compromised as plant photosynthetic capacity, biomass, and/or growth are reduced. To evaluate effects of disturbance on CO2 capture in plants we performed a five-month manipulative experiment in a tropical seagrass (Thalassia hemprichii) meadow exposed to two intensity levels of shading and simulated grazing. We assessed CO2 capture potential (as net CO2 fixation) using areal productivity calculated from continuous measurements of diel photosynthetic rates, and estimates of plant morphology, biomass and productivity/respiration (P/R) ratios (from the literature). To better understand the plant capacity to coping with level of disturbance we also measured plant growth and resource allocation. We observed substantial reductions in seagrass areal productivity, biomass, and leaf area that together resulted in a negative daily carbon balance in the two shading treatments as well as in the high-intensity simulated grazing treatment. Additionally, based on the concentrations of soluble carbohydrates and starch in the rhizomes, we found that the main reserve sources for plant growth were reduced in all treatments except for the low-intensity simulated grazing treatment. If permanent, these combined adverse effects will reduce the plants' resilience and capacity to recover after disturbance. This might in turn have long-lasting and devastating effects on important ecosystem functions, including the carbon sequestration capacity of the seagrass system.

Place, publisher, year, edition, pages
2017. Vol. 12, no 7, article id e0181386
National Category
Biological Sciences
Research subject
Plant Physiology
Identifiers
URN: urn:nbn:se:su:diva-145908DOI: 10.1371/journal.pone.0181386ISI: 000405649700131OAI: oai:DiVA.org:su-145908DiVA, id: diva2:1134698
Available from: 2017-08-21 Created: 2017-08-21 Last updated: 2018-04-30Bibliographically approved
In thesis
1. Seagrass productivity: from plant to system
Open this publication in new window or tab >>Seagrass productivity: from plant to system
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Seagrasses form one of the most productive habitats on earth and are recognized as very efficient carbon sinks. The levels and patterns of productivity within and across different seagrass systems vary widely due to natural or human-induced factors. Seagrass plants, being the foundation species of seagrass meadows, have a substitutional role as primary producers to the overall productivity of their habitat. Clarifying the variation in the carbon capture potential of these plants on physiological and ecological levels is essential to understand of the whole system’s carbon balance. In this thesis, the photosynthetic performance and productivity of seagrass plants were studied in relation to factors that have large impact on productivity, such as tissues age, season and water depth. Furthermore, the seagrass response, in terms of capacity to capture and sequester carbon, to human-induced stress factors such as shading and simulated grazing was evaluated in a tropical seagrass meadow. The research has included a multitude of seagrass productivity assessments from plant- to system level.

The results showed that age has a significant effect on the photosynthetic performance of the temperate seagrass Zostera marina L., both within a single shoot and between shoots. When comparing leaves among the same shoot, the photosynthetic capacity and efficiency were highest in mature tissues and significantly reduced in very young tissues as well as in tissues undergoing senescence. In response to high light stress, very young tissues seemed to cope better with dissipating excess light energy, which was demonstrated by the higher values of non-photochemical quenching (NPQ) observed compared to mature and senescent tissues. Such an effect was also observed when comparing the oldest and youngest shoots from the same genet; the youngest shoot showed higher ability to dissipate excess light energy compared to the oldest one, and might thus be able to better withstand light stress.

On a larger spatiotemporal scale, the areal productivity of seagrass plants was significantly affected by light availability and temperature, leading to a strong seasonal variation. In addition, depth had a strong site-specific effect on plant productivity in terms of biomass. On a yearly basis, productivity rates varied substantially, reaching up to 20 g C m-2 24h-1 in the summer months. This high carbon capture potential was, however, outbalanced by the high respiration rates of the benthic community. Overall, the whole system had a low but positive yearly carbon balance.

Both shading and simulated grazing negatively affected seagrass plants and the whole habitat after five months of experimental disturbance. On the plant level, photosynthesis, productivity and growth were all reduced. On the system level, a reduction in community productivity was recorded. The long-term refractory carbon was, however, not affected although erosion was observed in treatments subjected to simulated grazing.

In summary, this thesis has established that age, season, depth and exposure are factors highly responsible for natural variation in seagrass plant- and habitat productivity, and that seagrasses respond to human-induced stress by significantly reducing their productivity. Even though seagrass plants are generally capable of surviving stress periods, these results suggest that prolonged deteriorating stress conditions will lead to serious harm on the plants as well as the entire habitat, and thereby compromising the carbon burial capacity of the seagrass system.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University, 2018. p. 51
Keywords
Seagrass, Chlorophyll a fluorescence, Ageing, Productivity, Seasonality, Stress response
National Category
Botany Ecology
Research subject
Plant Physiology
Identifiers
urn:nbn:se:su:diva-155497 (URN)978-91-7797-116-0 (ISBN)978-91-7797-117-7 (ISBN)
Public defence
2018-06-08, Vivi Täckholmssalen (Q-salen), NPQ-huset, Svante Arrhenius väg 20, Stockholm, 10:00 (English)
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Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 2: Manuscript.

Available from: 2018-05-16 Created: 2018-04-23 Last updated: 2018-05-09Bibliographically approved

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