Underwater Photosynthesis and Internal Aeration of Submerged Terrestrial Wetland Plants
Submergence impedes plant gas exchange with the environment. Survival depends upon internal aeration to provide O2 throughout the plant body, although short-term anoxia can be tolerated. During nights, plants rely on O2 entry from the floodwater and pO2 i
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Abstract Submergence impedes plant gas exchange with the environment. Survival depends upon internal aeration to provide O2 throughout the plant body, although short-term anoxia can be tolerated. During nights, plants rely on O2 entry from the floodwater and pO2 in roots declines so that some tissues become severely hypoxic or even anoxic. Underwater photosynthesis is the main daytime O2 source and also provides sugars. Capacity for photosynthesis under water, like in air, is determined by available CO2 and light; however, slow diffusion in water often limits CO2 supply. Underwater photosynthesis in some wetland species is enhanced by gas films on superhydrophobic leaf surfaces. Leaf gas films also increase night-time O2 uptake by submerged plants. Flooding events are forecast to increase and understanding of plant submergence tolerance should enable predictions of possible impacts on vegetation communities and also aid breeding of improved submergence tolerance in rice.
1 The Submergence Environment The slow diffusion of gases in water compared with in air presents a challenge to submerged terrestrial plants (Armstrong 1979) as oxygen (O2) and carbon dioxide (CO2) uptake are greatly impeded. Diffusion of gases in water is approximately 10,000-fold slower than in air, so that since the diffusive boundary layers (DBLs) O. Pedersen (*) Freshwater Biological Laboratory, University of Copenhagen, Universitetsparken 4, 3rd floor, 2100 Copenhagen, Denmark Institute of Advanced Studies, The University of Western Australia, Crawley, WA 6009, Australia School of Plant Biology, The University of Western Australia, Crawley, WA 6009, Australia e-mail: [email protected] T.D. Colmer School of Plant Biology, The University of Western Australia, Crawley, WA 6009, Australia J.T. van Dongen and F. Licausi (eds.), Low-Oxygen Stress in Plants, Plant Cell Monographs 21, DOI 10.1007/978-3-7091-1254-0_16, © Springer-Verlag Wien 2014
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adjacent to surfaces are of similar thickness in both environments, the resulting apparent resistance to gas exchange is 10,000-fold higher when under water (Vogel 1994). Submerged aquatic plants have thus developed adaptive features of their leaves to reduce the DBL, and also to reduce other resistances (e.g. thin cuticle and thin leaves), to facilitate gas exchange in the aqueous environment (Sculthorpe 1967; Colmer et al. 2011). In addition to the slow diffusion of gases, the solubility of O2 in water is relatively low; 1 L of air contains 33-fold more O2 than 1 L of water at 20 C at sea level (Stumm and Morgan 1996). The amount of dissolved O2 in a particular water body is determined by a combination of the water temperature and salinity and the surrounding O2 partial pressure (pO2). The pO2 in the atmosphere decreases with elevation (at atmospheric equilibrium, less O2 is dissolved in the water of a mountain lake than at sea level) and increases with depth (the absolute pressure increases with 101 kPa per 10 m depth). Temperature and salinity can differ subst
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