Submergence tolerance in Hordeum marinum: dissolved CO₂ determines underwater photosynthesis and growth
2010
Floodwaters differ markedly in dissolved CO₂, yet the effects of CO₂ on submergence responses of terrestrial plants have rarely been examined. The influence of dissolved CO₂ on underwater photosynthesis and growth was evaluated for three accessions of the wetland plant Hordeum marinum Huds. All three accessions tolerated complete submergence, but only when in CO₂ enriched floodwater. Plants submerged for 7 days in water at air equilibrium (18μM CO₂) suffered loss of biomass, whereas those with 200μM CO₂ continued to grow. Higher underwater net photosynthesis at 200μM CO₂ increased by 2.7- to 3.2-fold sugar concentrations in roots of submerged plants, compared with at air equilibrium CO₂. Leaf gas films enhancing gas exchange with floodwater, lack of a shoot elongation response conserving tissue sugars and high tissue porosity (24-31% in roots) facilitating internal O₂ movement, would all contribute to submergence tolerance in H. marinum. The present study demonstrates that dissolved CO₂ levels can determine submergence tolerance of terrestrial plants. So, submergence experiments should be conducted with defined CO₂ concentrations and enrichment might be needed to simulate natural environments and, thus, provide relevant plant responses.
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