DOES LONG-TERM ELEVATION OF CO2 CONCENTRATION INCREASE PHOTOSYNTHESISIN FOREST FLOOR VEGETATION - INDIANA STRAWBERRY IN A MARYLAND FOREST

As the partial pressure of CO2 (pCO(2)) in the atmosphere rises, photo respiratory loss of carbon in C-3 photosynthesis will diminish and the net efficiency of light-limited photosynthetic carbon uptake should r ise. We tested this expectation for Indiana strawberry (Duchesnea indi ca) growing on a Maryland forest floor. Open-top chambers were used to elevate the pCO(2) of a forest floor habitat to 67 Pa and were paired with control chambers providing an ambient pCO(2) of 38 Pa. After 3.5 years, D. indica leaves grown and measured in the elevated pCO(2) sho wed a significantly greater maximum quantum efficiency of net photosyn thesis (by 22%) and a lower light compensation point (by 42%) than lea ves grown and measured in the control chambers. The quantum efficiency to minimize photorespiration, measured in 1% O-2, was the same for co ntrols and plants grown at elevated pCO(2). This showed that the maxim um efficiency of light-energy transduction into assimilated carbon was not altered by acclimation and that the increase in light-limited pho tosynthesis at elevated pCO(2) was simply a function of the decrease i n photorespiration. Acclimation did decrease the ribulose-1,5-bisphosp hate carboxylase/oxygenase and light-harvesting chlorophyll protein co ntent of the Leaf by more than 30%. These changes were associated with a decreased capacity for light-saturated, but not light-limited, phot osynthesis. Even so, leaves of D. indica grown and measured at elevate d pCO(2) showed greater light-saturated photosynthetic rates than leav es grown and measured at the current atmospheric pCO(2). In situ measu rements under natural forest floor lighting showed large increases in leaf photosynthesis at elevated pCO(2), relative to controls, in both summer and fall. The increase in efficiency of light-limited photosynt hesis with elevated pCO(2) allowed positive net photosynthetic carbon uptake on days and at locations on the forest floor that light fluxes were insufficient for positive net photosynthesis in the current atmos pheric pCO(2).