Seed yield after environmental stress in soybean grown under elevated CO2

Episodes of high temperature and drought are predicted to occur more frequently under conditions of future climate change. This study investigated whether an episode of high air temperature (HT, + 15 degrees C), water deficit (WD), or both (HTWD), for 8 d, had the same effects on the yield of soybean [Glycine max (L.) Merrill, cv. Fiskeby V] grown under either ambient (aCO(2); 360 micromol mol(-1) CO(2)) or elevated (eCO(2); 700 micromol mol(-1) CO(2)) CO(2) concentrations. Plants were grown in a glasshouse at either aCO(2) or at eCO(2) until 52 d after sowing (DAS). The 8-d stress treatments were then imposed before the plants were returned to their original environments. Across harvests, total biomass was 41% greater under eCO(2) than under aCO(2) but reduced by HT, WD, and HTWD under both CO(2) concentrations. The relative response of total biomass to HT, WD, and HTWD episodes was the same for plants grown under either aCO(2) or eCO(2). At maturity, seed dry weight and number per plant under eCO(2) were increased by an average of 32 and 22%, respectively, compared with aCO(2). The same parameters were reduced after HTWD by 29 and 30%, respectively, in aCO(2) and eCO(2). Seed filling was earlier under HT and HTWD. The rate of change in harvest index was unaltered by CO(2) while under HTWD, it decreased. Seed number explained 85% of the variation in yield, but yield was also related linearly to photosynthesis during seed filling, suggesting both are important determinants of yields under stress.