Effects Of Dirrerent Nitrogen Form And Water Stress On Nitrogen And Photosynthetic Physiology Of Rice(Oryza Sativas L.)

Rice is the most important cereal food crop in China, and consumes a large amount of water used in agricultural production. However, 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 in the rice production system is obtaining more and more concerns. In China, some field experiments and demonstrations were conducted to examine the effects of non-flooded mulching cultivation on rice yield, aiming to develop the water-saving irrigation system in rice production system. After planting under the non-flooded condition, two conditions have been changed; plentiful water supply is shifted to relative water stress, and nitrogen form absorbed by rice plants is inevitably shifted to the ratio of less ammonium to more nitrate in the soil due to the increased nitrification in non-flooded condition. Therefore the effects of different nitrogen forms on the growth, water and nitrogen uptake and utilization by rice plants under simulated water stress were studied in a hydroponics experiment by adding polyethylene glycol 6000 to solution. The results obtained are listed as follows:The growth of NO₃^--N supplied rice plants were significantly inhibited by water stress, however, no pronounced differences were found under NH₄⁺-N supply. Under ammonium nutrition there were no significant differences on biomass, leaf area, net photosynthetic rate, carboxylation efficiency of rice plant between water stress and non-water stress. However, under nitrate nutrition, the mentioned parameters decreased under water stress condition. The contents of chlorophyll a and chlorophyll b were higher in the rice plants supplied by ammonium under water stress than that of non-water stress. There were no significant different apparent quantum yield of rice plant supplied with three nitrogen forms between water stress and non-water stress.Under ammonium nutrition, there was no significant different CE of rice between water stress and non-water stress, while Rubisco activity was reduced 13.3% by water stress. However, under nitrate nutrition, both of CE and Rubisco content reduced under water stress, and Rubisco activity reduced 23.0%. Furthermore, water stress increased total nitrogen content in newly expanded leaf of rice supplied with ammonium, while no effects under nitrate supply. Water stress increased soluble protein content in newly expanded leaf supplied with three nitrogen forms, although no significant effect on the ratio of Rubisco content to soluble protein under ammonium supply, decreased this ratio under nitrate supply. Inhibitory effect of water stress on photosynthetic efficiency of rice plants supplied with ammonium was lower than that of supplied with nitrate. Under water stress, photosynthetic nitrogen use efficiency (PNUE) was decreased with NO₃^--N supply.The biomass of rice were not affected by partial-root water stress under those three nitrogen forms, but root parameters of sole nitrate supply decreased significantly under water stress compared to non-water stress part. Water stress stimulated the absorption of NO₃^--N. The photosynthesis rate was inhibited by water stress under NO₃^--N supply, but no effects under NH₄⁺-N supply.