Effect of the long-term elevation of CO sub 2 concentration in the field on the quantum yield of photosynthesis of the C sub 3 sedge, Scirpus olneyi

CO{sub 2} concentration was elevated throughout 3 years around stands of the C{sub 3} sedge Scirpus olneyi on a tidal marsh of the Chesapeake Bay. The hypothesis that tissues developed in an elevated CO{sub 2} atmosphere will show an acclimatory decrease in photosynthetic capacity under light-limiting conditions was examined. The absorbed light quantum yield of CO{sub 2} uptake ({phi}{sub abs}) and the efficiency of photosystem II photochemistry were determined for plants which had developed in open top chambers with CO{sub 2} 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 O{sub 2} to suppress photorespiration, shoots showed a {phi}{sub abs} of 0.093 {plus minus} 0.003, with no statistically significant difference between shoots grown in elevated or control CO{sub 2} concentration. Efficiency of photosystem II photochemistry was also unchanged by development in an elevated CO{sub 2} atmosphere. Shoots grown and measured in 680 micromoles per mole of CO{sub 2} in air showed a {phi}{sub abs} of 0.078 {plus minus} 0.004 compared with 0.065 {plus minus} for leaves grown and measured in 351 micromoles per mole CO{sub 2} in air; a highly significant increase. In accordance with the change in {phi}{sub abs}, the light compensation point of photosynthesis decreased from 51 {plus minus} 3 to 31 {plus minus} 3 micromoles per square meter per second for stems grown and measured in 351 and 680 micromoles per mole of CO{sub 2} in air, respectively.