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Regulated deficit irrigation (RDI) affects the physiological process of fruit trees. An experiment was conducted to evaluate physiological responses of pear tree to RDI treatments and its impacts on yield under desert climate in 2009 and 2010. Four water stress treatments consisted of moderate and severe (irrigated with 60% and 40% of pan evaporation, respectively) water deficit in the cell division or slow fruit enlargement stage and well irrigation (irrigated with 80% of pan evaporation) during other fruit growth stages. The results showed that leaf photosynthetic, transpiration rate and stomatal conductance all decreased during water stress cycle, and it took 1 to 4 weeks to recover these responses after the irrigation resuming depend on RDI treatments. After severe water stress in cell division stage or moderate water stress in slow fruit enlargement stage, leaf photosynthetic rate effectively enhanced during the fruit enlargement stage following resumption of well irrigation, resulting in the improvement of fruit yield. The leaf water use efficiency was also improved by RDI treatments. The results contributed to understand mechanisms of the yield improvement by RDI and its high water use efficiency. (C) 2015 Elsevier B.V. All rights reserved.