DOES LONG-TERM ELEVATION OF CO2 CONCENTRATION INCREASE PHOTOSYNTHESISIN FOREST FLOOR VEGETATION - INDIAN STRAWBERRY IN A MARYLAND FOREST (VOL 114, PG 337, 1997)

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 Indian strawberry (Duchesnea indic a) 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) show ed a significantly greater maximum quantum efficiency of net photosynt hesis (by 22%) and a lower light compensation point (by 42%) than leav es grown and measured in the control chambers. The quantum efficiency to minimize photorespiration, measured in 1% O-2, was the same for con trols and plants grown at elevated pCO(2). This showed that the maximu m efficiency of light-energy transduction into assimilated carbon was not altered by acclimation and that the increase in light-limited phot osynthesis at elevated pCO(2) was simply a function of the decrease in photorespiration. Acclimation did decrease the ribulose-1,5-bisphospb ate carboxylase/oxygenase and light-harvesting chlorophyll protein con tent of the leaf by more than 30%. These changes were associated with a decreased capacity for light-saturated, but not light-limited, photo synthesis. Even so, leaves of D. indica grown and measured at elevated pCO(2) showed greater light-saturated photosynthetic rates than leave s grown and measured at the current atmospheric pCO(2). In situ measur ements under natural forest floor lighting showed large increases in l eaf photosynthesis at elevated pCO(2), relative to controls, in both s ummer and fall. The increase in efficiency of light-limited photosynth esis with elevated pCO(2) allowed positive net photosynthetic carbon u ptake on days and at locations on the forest floor that light fluxes w ere insufficient for positive net photosynthesis in the current atmosp heric pCO(2).