Acclimation of peanut (Arachis hypogaea L.) leaf photosynthesis to elevated growth CO₂ and temperature

Peanut (Arachis hypogaea L. cv. Florunner) was grown from seed sowing to plant maturity under two daytime CO2 concentrations ([CO2]) of 360 micromol mol-1 (ambient) and 720 micromol mol-1 (elevated) and at two temperatures of 1.5 and 6.0 °C above ambient temperature. The objectives were to characterize peanut leaf photosynthesis responses to long-term elevated growth [CO2] and temperature, and to assess whether elevated [CO2] regulated peanut leaf photosynthetic capacity, in terms of activity and protein content of ribulose bisphosphate carboxylase-oxygenase (Rubisco), Rubisco photosynthetic efficiency, and carbohydrate metabolism. At both growth temperatures, leaves of plants grown under elevated [CO2] had higher midday photosynthetic CO2 exchange rate (CER), lower transpiration and stomatal conductance and higher water-use efficiency, compared to those of plants grown at ambient [CO2]. Both activity and protein content of Rubisco, expressed on a leaf area basis, were reduced at elevated growth [CO2]. Declines in Rubisco under elevated growth [CO2] were 27-30% for initial activity, 5-12% for total activity, and 9-20% for protein content. Although Rubisco protein content and activity were down-regulated by elevated [CO2], Rubisco photosynthetic efficiency, the ratio of midday light-saturated CER to Rubisco initial or total activity, of the elevated-[CO2] plants was 1.3- to 1.9-fold greater than that of the ambient-[CO2] plants at both growth temperatures. Leaf soluble sugars and starch of plants grown at elevated [CO2] were 1.3- and 2-fold higher, respectively, than those of plants grown at ambient [CO2]. Under elevated [CO2], leaf soluble sugars and starch, however, were not affected by high growth temperature. In contrast, high temperature reduced leaf soluble sugars and starch of the ambient-[CO2] plants. Activity of sucrose-P synthase, but not adenosine 5'-diphosphoglucose pyrophosphorylase, was up-regulated under elevated growth [CO2]. Thus, in the absence of other environmental stresses, peanut leaf photosynthesis would perform well under rising atmospheric [CO2] and temperature as predicted for this century.