Growth temperature can alter the temperature dependent stimulation of photosynthesis by elevated carbon dioxide in Albutilon theophrasti

Stimulation of photosynthesis in response to elevated carbon dioxide concen tration [CO2] in the short-term (min) should be highly temperature dependen t at high photon flux. However, it is unclear if long-term (days, weeks) ad aptation to a given growth temperature alters the temperature-dependent sti mulation of photosynthesis to [CO2]. In velveltleaf (Albutilon theophrasti) , the response of photosynthesis, determined as CO2 assimilation, was measu red over a range of internal CO2 concentrations at 7 short-term measurement (12, 16, 20, 24, 28, 32, 36 degreesC) temperatures for each of 4 long-term growth (16, 20, 28 and 32 degreesC) temperatures. In vivo estimates of V-C max, the maximum RuBP saturated rate of carboxylation, and J(max), the ligh t-saturated rate of potential electron transport, were determined from gas exchange measurements for each temperature combination. Overall, previous e xposure to a given growth temperature adjusted the optimal temperatures of J(max) and V-Cmax with subsequently greater enhancement of photosynthesis a t elevated [CO2] (i.e., a greater enhancement of photosynthesis at elevated [CO2] was observed at low measurement temperatures for A. theophrasti grow n at low growth temperatures compared with higher growth temperatures, and vice verse for plants grown and measured at high temperatures), Previous bi ochemical based models used to predict the interaction between rising [CO2] and temperature on photosynthesis have generally assumed no growth tempera ture effect on carboxylation kinetics or no limitation by J(max), In the cu rrent study, these models over predicted the temperature dependence of the photosynthetic response to elevated [CO2] at temperatures above 24 degreesC . If these models are modified to include long-term adjustments of J(max) a nd V-Cmax to growth temperature, then greater agreement between observed an d predicted values was obtained.