Can elevated CO2 combined with high temperature ameliorate the effect of terminal drought in wheat?

Wheat (Triticum aestivum L.) production may be affected by the future climate, but the impact of the combined increases in atmospheric CO2 concentration, temperature and incidence of drought that are predicted has not been evaluated. The combined effect of elevated CO2, high temperature and terminal drought on biomass accumulation and grain yield was evaluated in vigorous (38-19) and nonvigorous (Janz) wheat genotypes grown under elevated CO2 (700 mu L L-1) combined with temperatures 2 degrees C, 4 degrees C and 6 degrees C above the current ambient temperature. Terminal drought was induced in all combinations at anthesis in a split-plot design to test whether the effect of elevated CO2 combined with high temperature ameliorates the negative effects of terminal drought on biomass accumulation and grain yield. Biomass and grain yield were enhanced under elevated CO2 with 2 degrees C above the ambient temperature, regardless of the watering regimen. The combinations of elevated CO2 plus 4 degrees C or 6 degrees C above the ambient temperature did not enhance biomass and grain yield, but tended to decrease them. The reductions in biomass and grain yield (45-50%) caused by terminal drought were less severe (21-28%) under elevated CO2 with 2 degrees C above the ambient temperature. The amelioration resulted from a 63% increase in the rate of leaf net photosynthesis in 38-19 and a 39% increase in tillering and leaf area in Janz. The contrasting responses and phenological development of these two genotypes to the combination of elevated CO2, temperature and terminal drought, and the possible influences on their source-sink relationships are discussed.