Effect of the long-term elevation of CO2 concentration in the field on the quantum yield of photosynthesis of the C3 sedge, Scirpus olneyi

CO2 concentration was elevated throughout 3 years around stands of the C3 sedge Scirpus olneyi on a tidal marsh of the Chesapeake Bay. The hypothesis that tissues developed in an elevated CO2 atmosphere will show an acclimatory decrease in photosynthetic capacity under light-limiting conditions was examined. The absorbed light quantum yield of CO2 uptake (φabs) and the efficiency of photosystem II photochemistry were determined for plants which had developed in open top chambers with CO2 concentrations in air of 680 micromoles per mole, and of 351 micromoles per mole as controls. When measured in an atmosphere with 10 millimoles per mole O2 to suppress photorespiration, shoots showed a φabs of 0.093 ± 0.003, with no statistically significant difference between shoots grown in elevated or control CO2 concentration. Efficiency of photosystem II photochemistry was also unchanged by development in an elevated CO2 atmosphere. Shoots grown and measured in 680 micromoles per mole of CO2 in air showed a φabs of 0.078 ± 0.004 compared with 0.065 ± for leaves grown and measured in 351 micromoles per mole CO2 in air; a highly significant increase. In accordance with the change in φabs, the light compensation point of photosynthesis decreased from 51 ± 3 to 31 ± 3 micromoles per square meter per second for stems grown and measured in 351 and 680 micromoles per mole of CO2 in air, respectively