Internationally there has been extensive research on the impact of climate change on water use efficiency (WUE) of plants. Ogaya and Peuelas (2003) showed that plants maintained higher WUE due to drought in arid and semi-arid areas, thus reducing the influence of water deficit and enhancing competitiveness for water in drought conditions. Tenhunen et al. (2002) found that temperature rise had accelerated transpiration of plants and evaporation of soil water in arid and semi-arid areas and affected WUE of crops. With the reduced soil water content, the lowered WUE of plant ecosystems indicates that lowered photosynthetic rates of plants in extreme drought conditions are caused by factors other than stomatal factors. A study by Zhao et al. (2007) showed that the net photosynthetic rate and stomatal conductance of spring wheat leaves in semi-arid areas at grain filling and milk stage decreased with increased temperature, and transpiration rate had increased. Climate warming inhibits photosynthesis and dry matter accumulation of spring wheat and consequently affects WUE