| Rice is the most important cereal food crop in China, and consumes a large amount of water utilized in agricultural production and water use efficiency (WUE) is very low. In rice production system, more than 80% of the total water irrigated is lost through evaporation and leakage, less than 20% is transpired by rice plants themselves. This so-called ecological water waste is obtaining more and more concerns. Some field experiments and demonstrations have been conducted aiming at increase of water use efficiency and develop the water-saving irrigation system in rice production system. In non-flooded cultivation of rice, two conditions have been changed:(1) nitrogen form absorbed by rice plants is inevitably shifted to the ratio of less ammonium to more nitrate; (2) plentiful water supply is shifted to relative water stress. Therefore, it is proposed that the growth of rice plants under water stress is related to nitrogen form and water stress.In order to study the responses of different nitrogen forms supplied indica and japonica rice seedlings to water stress, experiments supplied with different nitrogen forms and simulated water stress by adding 100g·L-1polyethylene glycol 6000 (PEG6000) were conducted. The results showed that:(1) Water stress suppressed biomass and photosynthesis in nitrate supplied rice seedlings, while did not decrease in ammonium supplied rice seedlings, and in reverse significant increased photosynthesis under ammonium nutrition;(2) Under water stress, the accumulation of amino acid resulted in a decrease in leaf osmotic potential. The positive relationship between leaf osmotic potential and leaf transpiration rate indicated that the declined transpiration rate might be accompanied by the decreased leaf transpiration;(3) Under water stress conditions, higher activity of NR and GS were found in ammonium supplied rice compared with nitrate supplied rice, and the content of soluble sugar and soluble protein are significantly higher in ammonium supplied rice.Accompanied with the decreased leaf osmotic potential, ammonium nutrition maintained or increased leaf water content under water stress. There was positive relationship between leaf water content and photosynthesis, maintainance or increase in leaf water content in ammonium nutrition assured leaf photosynthesis and plant growth under water stress, and thus enhanced tolerance of rice seedlings to water stress. |
