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Beyond carbon-limitation: A re-evaluation of the ecological role of photorespiration and direct oxygen photoreduction in seagrasses
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
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 [en]
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: urn:nbn:se:su:diva-99434ISBN: 978-91-7447-850-1 (print)OAI: oai:DiVA.org:su-99434DiVA: diva2:687018
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
List of papers
1. Photosynthetic activity of seagrasses and macroalgae in temperate shallow waters can alter seawater pH and total inorganic carbon content at the scale of a coastal embayment
Open this publication in new window or tab >>Photosynthetic activity of seagrasses and macroalgae in temperate shallow waters can alter seawater pH and total inorganic carbon content at the scale of a coastal embayment
2013 (English)In: Marine and Freshwater Research, ISSN 1323-1650, E-ISSN 1448-6059, Vol. 64, no 11, 1040-1048 p.Article in journal (Refereed) Published
Abstract [en]

Many studies have reported fluctuations in pH and the concentration of dissolved inorganic carbon (DIC) in shallow coastal waters as a result of photosynthetic activity; however, little is known about how these fluctuations vary with degree of exposure among habitats, and at different scales. In the present study, diel variation in seawater pH was apparent in aquaria experiments with Zostera marina and Ruppia maritima. These pH variations were affected by light regime, biomass level and plant species. Subsequently, the natural variability in seawater pH and the concentration of DIC was assessed in six shallow embayments (three sheltered and three exposed) during sunny days. From the outer part towards the interior part of each bay, the following four habitats were identified and studied: the bay-mouth open water, seagrass beds, mixed macrophyte belts and unvegetated bottoms. The two vegetated habitats and unvegetated bottoms were characterised by higher pH and a lower concentration of DIC than in the bay-mouth water. The mixed macrophytes habitat showed slightly higher pH and a lower concentration of DIC than the seagrass and unvegetated habitats. No significant effect of exposure was detected. Our findings clearly showed that the photosynthetic activity of marine macrophytes can alter the coastal pH and the concentration of DIC and that the effects can be observed at the scale of a whole bay.

Keyword
ocean acidification, temperate environment
National Category
Biological Sciences Oceanography, Hydrology, Water Resources
Identifiers
urn:nbn:se:su:diva-96674 (URN)10.1071/MF12124 (DOI)000326166400005 ()
Note

AuthorCount:3;

Available from: 2013-11-26 Created: 2013-11-25 Last updated: 2017-12-06Bibliographically approved
2. Photorespiration and carbon limitation determine productivity in temperate seagrasses
Open this publication in new window or tab >>Photorespiration and carbon limitation determine productivity in temperate seagrasses
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.

National Category
Botany
Research subject
Plant Physiology
Identifiers
urn:nbn:se:su:diva-100015 (URN)10.1371/journal.pone.0083804 (DOI)000328745100145 ()
Available from: 2014-01-23 Created: 2014-01-23 Last updated: 2017-12-06Bibliographically approved
3. Roles of alternative electron flows to O2 and non-photochemical quenching during photosynthesis in the seagrass Zostera marina
Open this publication in new window or tab >>Roles of alternative electron flows to O2 and non-photochemical quenching during photosynthesis in the seagrass Zostera marina
(English)Manuscript (preprint) (Other academic)
National Category
Biological Sciences
Identifiers
urn:nbn:se:su:diva-100156 (URN)
Available from: 2014-01-28 Created: 2014-01-28 Last updated: 2014-01-28Bibliographically approved
4. Does electron flow via photorespiration mitigate photoinhibition in the seagrass Zostera marina?
Open this publication in new window or tab >>Does electron flow via photorespiration mitigate photoinhibition in the seagrass Zostera marina?
(English)Manuscript (preprint) (Other academic)
National Category
Biological Sciences
Identifiers
urn:nbn:se:su:diva-100157 (URN)
Available from: 2014-01-28 Created: 2014-01-28 Last updated: 2014-01-28Bibliographically approved

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