Elevated growth CO 2 delays drought stress and accelerates recovery of rice leaf photosynthesis

Abstract

Rising atmospheric carbon dioxide concentration ([CO 2]) and predicted changes in rainfall frequency and intensity could have considerable impact on crop growth and yield. Our objective was to assess rice leaf photosynthesis and carbohydrate metabolism in response to decreased soil water availability at elevated growth [CO 2]. Rice ( Oryza sativa [L.] cv. IR-72) was grown season-long in eight sunlit, controlled-environment chambers at two daytime [CO 2] of 350 μmol mol −1 (ambient) and 700 μmol mol −1 (elevated). Drought stress was imposed during panicle initiation and anthesis growth phases. At elevated [CO 2], midday leaf photosynthetic CO 2 exchange rates (CER) and concentrations of chlorophyll (Chl) were higher at most sampling dates, whereas total soluble protein (TSP) decreased on several sampling dates, compared with plants at ambient [CO 2]. Furthermore, elevated [CO 2] increased midday leaf sucrose-phosphate synthase (SPS) activity throughout the season, and enhanced midday leaf sucrose and starch accumulation during early reproductive phases, but not during later reproductive phases. Near the end of drought periods, water deficit caused substantial decreases in midday leaf CER and concentrations of Chl and TSP, with concomitant reductions in photosynthetic primary products and SPS activity. These drought-induced effects were more severe for plants grown at ambient than at elevated [CO 2]. Plants grown under elevated [CO 2] were able to maintain midday leaf photosynthesis, and to some extent other photosynthetic-related parameters, longer into the drought period than plants grown at ambient [CO 2]. In addition, midday leaf CER recovered from water deficit more rapidly in the elevated [CO 2] treatment. Thus, in the absence of other potential climate stresses, rice grown under future increases in atmospheric [CO 2] may be better able to tolerate drought situations.