Submergence Tolerance of the Wetland Plant Hordeum marinum
Pedersen, O., Malik, A. and Colmer, T.D. 2010. Submergence tolerance in Hordeum marinum: dissolved CO2 determines underwater photosynthesis and growth. Functional Plant Biology 37: 524-531.
To learn how the wetland plant Hordeum marinum Huds. would respond when fully submerged in water, Pedersen et al. grew several 28-day-old plants consisting of three Nordic Gene Bank accessions (H21, H90 and H546) for seven additional days while exposing them to four different treatments: "aerated root zone controls with shoots in air; stagnant root zone with shoots in air; stagnant root zone with shoots also completely submerged with 18 µM CO2 (air equilibrium); stagnant root zone with shoots also completely submerged with 200 µM CO2 (simulating CO2 enrichment in many natural flood waters)," while measuring numerous plant responses.
The three researchers report that "plants submerged for 7 days in water at air equilibrium (18 µM CO2) suffered loss of biomass, whereas those with 200 µM CO2 continued to grow," and in this regard, they say that "higher underwater net photosynthesis at 200 µM CO2 increased by 2.7- to 3.2-fold sugar concentrations in roots of submerged plants, compared with at air equilibrium CO2." And they say that this phenomenon "is likely to have contributed to the greater root growth in submerged plants with the higher CO2 supply." In addition, they note that the latter CO2-enriched plants "tillered similarly to plants with shoots in air."
Pedersen et al. note that in addition to their findings, CO2 enrichment of submerging water to ~290 µM enhanced by 2-fold the growth of two cultivars of rice, compared to plants submerged with water in equilibrium with normal ambient air (Setter et al., 1989); and they further note that such elevated CO2 concentrations "have been reported at various field sites," citing the work of Setter et al. (1987) and Ram et al. (1999). Hence, they note the significance of this phenomenon for plants experiencing submergence during floods, indicating that under water in equilibrium with air of normal CO2 concentration, such plants typically lose mass and die, while when the water is super-saturated with CO2, they can not only survive, they can actually continue to grow.
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