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Photorespiration and carbon limitation determine productivity in temperate seagrasses
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Prince Songkla University, Thailand.
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.
2013 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, no 12, e83804Article in journal (Refereed) Published
Abstract [en]

The gross primary productivity of two seagrasses, Zostera marina and Ruppia maritima, and one green macroalga, Ulva intestinalis, was assessed in laboratory and field experiments to determine whether the photorespiratory pathway operates at a substantial level in these macrophytes and to what extent it is enhanced by naturally occurring shifts in dissolved inorganic carbon (DIC) and O2 in dense vegetation. To achieve these conditions in laboratory experiments, seawater was incubated with U. intestinalis in light to obtain a range of higher pH and O2 levels and lower DIC levels. Gross photosynthetic O2 evolution was then measured in this pretreated seawater (pH, 7.8–9.8; high to low DIC:O2 ratio) at both natural and low O2concentrations (adjusted by N2 bubbling). The presence of photorespiration was indicated by a lower gross O2 evolution rate under natural O2 conditions than when O2 was reduced. In all three macrophytes, gross photosynthetic rates were negatively affected by higher pH and lower DIC. However, while both seagrasses exhibited significant photorespiratory activity at increasing pH values, the macroalga U. intestinalis exhibited no such activity. Rates of seagrass photosynthesis were then assessed in seawater collected from the natural habitats (i.e., shallow bays characterized by high macrophyte cover and by low DIC and high pH during daytime) and compared with open baymouth water conditions (where seawater DIC is in equilibrium with air, normal DIC, and pH). The gross photosynthetic rates of both seagrasses were significantly higher when incubated in the baymouth water, indicating that these grasses can be significantly carbon limited in shallow bays. Photorespiration was also detected in both seagrasses under shallow bay water conditions. Our findings indicate that natural carbon limitations caused by high community photosynthesis can enhance photorespiration and cause a significant decline in seagrass primary production in shallow waters.

Place, publisher, year, edition, pages
2013. Vol. 8, no 12, e83804
National Category
Botany
Research subject
Plant Physiology
Identifiers
URN: urn:nbn:se:su:diva-100015DOI: 10.1371/journal.pone.0083804ISI: 000328745100145OAI: oai:DiVA.org:su-100015DiVA: diva2:690441
Available from: 2014-01-23 Created: 2014-01-23 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Beyond carbon-limitation: A re-evaluation of the ecological role of photorespiration and direct oxygen photoreduction in seagrasses
Open this publication in new window or tab >>Beyond carbon-limitation: A re-evaluation of the ecological role of photorespiration and direct oxygen photoreduction in seagrasses
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Seagrasses living in shallow coastal waters are regularly subjected to changes in environmental conditions including the two essential factors for photosynthesis: dissolved inorganic carbon (DIC) and irradiance. This thesis focuses on the photosynthetic responses of seagrasses to carbon limitation induced by community metabolism and/or high light intensities. Field sampling conducted in seagrass-dominated embayments along the Swedish west coast revealed that high pH and low levels of DIC caused by community photosynthesis are common in shallow coastal waters. These effects were found on a scale of a whole bay and were affected by the composition of the vegetation. Such carbon limitation and at the same time an increase in O2 concentration negatively affected photosynthesis of the seagrass species Zostera marina L. and Ruppia maritima L. by compromising carbon assimilation as well as enhancing photorespiration.  In contrast to the results from the two seagrasses, it was found that gross photosynthetic rates did not increase under low O2 concentrations in the green alga Ulva intestinalis L., suggesting that its efficient carbon acquisition mechanisms are able to suppress photorespiration. The role of photorespiration in seagrass photosynthesis was further investigated in Z. marina. It was found that under conditions of carbon limitation, photorespiration provides the major alternative sink for electrons, sustaining substantial electron transport via photosystem II while the Mehler reaction has a smaller contribution as an alternative electron sink. Photorespiration was however not a significant component of the photoprotective mechanisms in Z. marina under high irradiance. Here the down-regulation of electron transport via non-photochemical quenching appeared to be the more efficient mechanism for dissipating excess energy. Overall, this study highlights the role of O2 in seagrass photosynthesis which appears to be of greater importance than previously envisaged, particularly in the productive waters where carbon availability is occasionally limited. 

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University, 2014. 49 p.
Keyword
Carbon limitation, Chlorophyll fluorescence, Electron transport rate, Irradiance, Mehler reaction, Non-photochemical quenching, Photorespiration, Photosynthetic activity
National Category
Botany
Research subject
Plant Physiology
Identifiers
urn:nbn:se:su:diva-99434 (URN)978-91-7447-850-1 (ISBN)
Public defence
2014-02-21, Föreläsningssalen, Institutionen för Ekologi, Miljö och Botanik, Lilla Frescativägen 5, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2014-01-30 Created: 2014-01-13 Last updated: 2014-01-28Bibliographically approved
2. Seagrass Respiration: An assessment of oxygen consumption patterns of temperate marine macrophytes
Open this publication in new window or tab >>Seagrass Respiration: An assessment of oxygen consumption patterns of temperate marine macrophytes
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In coastal seas, the abundance of marine macrophytes has profound influence on the flows of oxygen and inorganic carbon through the water. Vast amounts of carbon dioxide are taken up by photosynthesis and part of this is respired back into the water column. The photosynthetic carbon uptake of the most common seagrasses of the northern hemisphere is nowadays extensively studied at both community- and individual levels, and its impact on coastal carbon- and oxygen fluxes is quite well defined. However, the coinciding release of carbon dioxide and consumption of oxygen by the processes of mitochondrial respiration and photorespiration in these organisms has as yet not been given much attention, especially concerning how these processes are affected by external factors. For estimations of the rates of mitochondrial respiration, the common approach has been to use values obtained during darkness and treat them as being constant over the day. This approach is questioned in this thesis where the effects of different abiotic and biotic factors on oxygen consumption were examined to elucidate possible variations of seagrass respiration rates (with primary focus on the species Zostera marina), explored mainly using gas exchange techniques. The initial aim was to investigate whether the rates of respiration are at all fluctuating. This was found to be the case. Secondly, impacts of various factors on the respiration process were examined on Z. marina, with additional studies on the seagrass Ruppia maritima and the common green alga Ulva intestinalis. It was found that respiration rates were lower in the light for all three species. Specific investigations on Z. marina showed that respiration rates also varied with time of the day. Moreover, the rates of both respiration and photosynthesis differed between Z. marina shoots of different age as well as among different parts of the leaves. These differences were observed at both ambient (19.1oC) and elevated (29.1oC) temperatures. Photorespiration, previously considered insignificant in seagrasses, was found to have a profound role, as high rates were observed in productive bays, i.e. in settings with low inorganic carbon availability and high oxygen. Overall, this thesis has identified important external and developmental factors influencing the patterns of oxygen consumption and associated carbon dioxide release of two common temperate seagrasses. Clearly, respiration in seagrasses is a dynamic process that responds to a variety of external and developmental factors, which should be carefully considered when assessing the carbon budget of coastal vegetated areas.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University, 2015. 54 p.
Keyword
Mitochondrial respiration, Photorespiration, Seagrass productivity, Zostera marina, Marine carbon budgets, Ruppia maritima, Ulva intestinalis
National Category
Other Biological Topics
Research subject
Plant Physiology
Identifiers
urn:nbn:se:su:diva-120156 (URN)978-91-7649-230-7 (ISBN)
Public defence
2015-10-09, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript.

Available from: 2015-09-17 Created: 2015-09-02 Last updated: 2015-09-16Bibliographically approved

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