Underwater photosynthesis and respiration in leaves of submerged wetland plants: gas films improve CO2 and O2 exchange
Many wetland plants have gas films on submerged leaf surfaces. We tested the hypotheses that leaf gas films enhance CO2 uptake for net photosynthesis (PN) during light periods, and enhance O2 uptake for respiration during dark periods. Leaves of four wetland species that form gas films, and two species that do not, were used. Gas films were also experimentally removed by brushing with 0.05% (v/v) Triton X. Net O2 production in light, or O2 consumption in darkness, was measured at various CO2 and O2 concentrations. When gas films were removed, O2 uptake in darkness was already diffusion-limited at 20.6 kPa (critical O2 pressure for respiration, COPR ≥ 284 mmol O2 m−3), whereas for some leaves with gas films, O2 uptake declined only at approx. 4 kPa (COPR 54 mmol O2 m−3). Gas films also improved CO2 uptake so that, during light periods, underwater PN was enhanced up to sixfold. Gas films on submerged leaves enable continued gas exchange via stomata and thus bypassing of cuticle resistance, enhancing exchange of O2 and CO2 with the surrounding water, and therefore underwater PN and respiration.The study is published in:
Colmer TD, Pedersen O (2008) Underwater photosynthesis and respiration in leaves of submerged wetland plants: gas films improve CO2 and O2 exchange. New Phytologist 177: 918-926.
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Underwater photosynthesis of submerged plants – recent advances and methods
We describe the general background and the recent advances in research on underwater photosynthesis of leaf segments, whole communities, and plant dominated aquatic ecosystems and present contemporary methods tailor made to quantify photosynthesis and carbon fixation under water. The majority of studies of aquatic photosynthesis have been carried out with detached leaves or thalli and this selectiveness influences the perception of the regulation of aquatic photosynthesis. We thus recommend assessing the influence of inorganic carbon and temperature on natural aquatic communities of variable density in addition to studying detached leaves in the scenarios of rising CO2 and temperature. Moreover, a growing number of researchers are interested in tolerance of terrestrial plants during flooding as torrential rains sometimes result in overland floods that inundate terrestrial plants. We propose to undertake studies to elucidate the importance of leaf acclimation of terrestrial plants to facilitate gas exchange and light utilization under water as these acclimations influence underwater photosynthesis as well as internal aeration of plant tissues during submergence.
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