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 μmol mol−1 (ambient) and 720 μmol 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.