Abstract
The negative effects of water stress on rice can be alleviated by NH4+ nutrition. However, the effects of mixed nitrogen (N) nutrition (NO3‐+NH4+) on resistance to water stress are still not well known. To investigate the response of rice growth to water stress and its relationship with photosynthetic characteristics, a hydroponic experiment supplying different N forms was conducted. Compared with NO3‐ nutrition, mixed‐N and NH4+ nutrition greatly alleviated the reduction of leaf area, chlorophyll content, and photosynthesis under water stress, whilst subsequently maintaining higher biomass. In contrast, water stress inhibited the root:shoot ratios in NH4+‐ and mixed‐N‐supplied plants, indicating reduced root growth and higher photosynthate availability to shoots. The following key observations were made: (1) a similar stomatal limitation and low proportion of activated Rubisco were observed among the three different N nutrition regimes; (2) increased mesophyll conductance in NH4+‐ and mixed‐N‐supplied plants simultaneously stimulated leaf photosynthesis and improved the water use efficiency, and (3) the maximum carboxylation rate and actual photochemical efficiency of photosystem II in NH4+‐ and mixed‐N‐supplied plants were significantly higher than that in NO3‐‐supplied plants, thus resulting in higher photochemical efficiency under water stress. In conclusion, mixed‐N and NH4+ nutrition may be used to develop strategies for improved water stress resistance and stimulated biomass production under conditions of osmotic stress and possibly drought.
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