International Journal of Plant Production 6 (4), October 2012 ISSN: 1735-6814 (Print), 1735-8043 (Online) http://ijpp.gau.ac.ir GUASNR Effects of climate change on water use efficiency in rain-fed plants N. Mi, Y.S. Zhang*, R.P. Ji, F. Cai, S.J. Zhang, X.L, Zhao Institute of Atmospheric Environment, China Meteorological Administration (Shenyang). *Corresponding author. E-mail:
[email protected] Received 13 April 2012; Accepted after revision 4 July 2012; Published online 15 August 2012 Abstract Water use efficiency (WUE) reflects the coupling of the carbon and water cycles and is an effective integral trait for assessing the responses of vegetated ecosystems to climate change. In this study, field experiments were performed to examine leaf WUE (WUEleaf) in response to changes in CO2 concentration and other environmental variables, including soil moisture and air temperature. We also used yield of maize and soybean, soil water content and precipitation data to calculate water use efficiency at the level of grain yield (WUEgrain) in a manner that enabled us to analyze the effects of climatic factors on WUEgrain. The results showed that the WUEleaf measurements of maize and soybean plants were negatively correlated with soil moisture and air temperature. At a photosynthetically active radiation (PAR) of -2 -1 1.600 μmol m s , increasing ambient CO2 concentrations (from 400 to 800 μmol -1 mol ) improved WUEleaf by 52.0% and 75.8% for maize (a C4 species) and soybean (a C3 species), respectively. Increased annual precipitation stimulated maize WUEgrain up to levels of approximately 500-550 mm, although maize WUEgrain decreased when annual precipitation exceeded 550 mm.