Winter wheat water requirement and utilization efficiency under simulated climate change conditions: A Penman-Monteith model evaluation

Impact of climate change on water supply and use is a critical issue for dryland crop production. In this study is assessed the potential impact of atmospheric CO2 enrichment (500 μmol mol−1, CE) and canopy warming (+2 °C, WA) and their combination (CW) on crop water utilization efficiency (WUE) of winter wheat in an open-air field experiment from Southeast China. Micro-meteorological measurement and wheat growth under individual treatments over three executive years of 2012-2015 were used to estimate the crop water requirement (CWR) of wheat using an improved FAO Penman-Monteith equation. Overall, CO2 enrichment slightly decreased the CWR by 8.3%, and increased the WUE of grain production (WUEg) by 23.1%, averaged over the three years. In contrast, warming increased CWR by 19.6% but decreased WUEg by 27.9% over the period. Under CW treatment, however, CWR was increased by 3.1-15.8% but WUEg was decreased by 3.5-18.2% throughout three years. Clearly, the positive impact of CO2 enrichment on WUE was largely negated under canopy warming. Moreover, when assessing with individual year data, inter-annual variability of WUEg was insignificant under WA, smaller under CE but much higher under CW, compared to CK. These results indicated that an interaction by canopy warming overshadowed the potential increase in WUE with CO2 enrichment and enforced yearly fluctuation of the crop production under simulated climate change conditions. Therefore, improving water supply and management in agriculture should thus be endeavored to address the potential constraints with future trends of concurrent atmospheric CO2 enrichment and warming.