Effects Of Different Water Stress And Nitrogen Forms On The Growth And Nitrogen Uptake Of Different Genotypes Rice And Its Physiological Mechanism

Influences of water and nitrogen nutrition are the principal factors on growth and development, nutrient absorption, yield formation in rice. At present, water-saving rice cultivation, improve nitrogen fertilizer using efficiency have become two hot topics of agricultural production research. With implementation of management measures on water-saving cultivation of rice, may lead to changes in soil ecological environment. Subsequently, soil nitrate nitrogen increases significantly and becomes the most important nitrogen source. Therefore, the systematic research concerning the influence of water stress and nitrogen forms on rice physiological growth, nitrogen metabolism, nitrogen absorption and utilization have important significance. In this paper, different rice genotypic varieties including Gangyou 527, Yangdao 6, Zhonghan 3 and Nongken 57 were used as materials under different water stress and nitrogen forms conditions, and water culture, pot and micro-plot field experiments were conducted. Effects of water stress and nitrogen forms on the grain yield, nitrogen metabolism, nitrogen absorption and utilization, and their physiological mechanism were investigated. The main results are as follows:1. Effects of hydropriming and polyethylene glycol (PEG) priming on germination and seedling growth of different genotypic rice under water stressThe results showed that significant higher levels of proline and soluble protein (SP) and lower levels of total soluble sugars and the content of malonicdialdehyde (MDA) in primed seeds were observed as compared with control (nonprimed seeds). Priming accelerated the process of glucose metabolism, improved the activities of phenylalanine ammonia lyase (PAL), superoxide (SOD), catalase (CAT) and peroxidase (POD) in stressed different genotypic rice seeds, moreover, priming effects was relatively significant. Rice seeds could be initiated significantly better by the priming of proper PEG concentration than hydropriming. The results showed that the best reaction conditions was 20%PEG content of hybrid indica rice seeds, but the best reaction conditions was 10%-15%PEG content of conventional japonica rice seeds. It can be damaged by permeability stress and inhibited normal germination of rice seeds if it beyond the threshold value of PEG content, respective. Response of hydroprimed seeds or PEG primed seeds on seedlings growth of different genotypic rice under different water stress. The results showed that, water stress could excite material metabolism, make against rice seeds germination, beneficial to significantly increase kinds of physiological index of seedlings in different genotypic rice, such as morphological index and protective enzymes after the treatment of proper PEG content. But it went against and inhibited germination in serious water stress treatment of rice seedlings. It showed that although seed priming treatment can improve activity of rice seedlings, but the coordination ability of the reaction external germinating environment excited by self-regulation were limited. It also indicated that indica rice had greater PEG tolerance than conventional japonica rice, but better priming effects were observed in hybrid indica rice.2. Effects of water stress on seedling growth of rice and its physiological basisWater stress was caused by adding PEG-6000 into the solution. Slight water stress (PEG≤5%, Water potential≥-0.05 MPa) has little effects on contents of amino acid nitrogen, soluble protein and activities of nitrate reductase (NR), glutamine synthetase (GS), glutamate synthase (GOGAT), glutamate dehydrogenase(GDH), glutamic-oxalacetic transaminase (GOT) and glutamic-pyruvic transaminase (GPT), and moreover the absorption and accumulation of nitrate nitrogen are stimulated. However, photosynthetic rate and dry matter accumulation are significantly inhibited. The dry matter accumulation change is significantly correlated with the regulation of photosynthetic rate more than that positive effect of resisting badness effect from environment. Therefore, photosynthetic rate has much more effect on dry matter accumulation than metabolism in vivo of rice. When PEG concentration≥10%(Water Potential≤-0.15 MPa), the concentrations of different nitrogen forms, some key enzymes of nitrogen metabolism and photosynthetic rate are significantly decreased. These effects on roots under the water stress are significantly larger than those on leaves. The above results indicate concentrations of different nitrogen forms and some key enzymes of nitrogen metabolism and photosynthetic rate are closely related to the intensity of water stress. 3. Effect of partial replacement of ammonium by nitrate on some physiological characteristics by genotypes of rice at the seedlings stage under moderate water stressUnder normal water condition, moderate reduce the ratio of ammonium/nitrate nitrogen (ammonium/nitrate ratio is 50:50), had little effects on contents of amino acid nitrogen (AA-N), soluble protein, photosynthetic rate, nitrogen uptake, and activities of NR, GS, GOGAT, GDH, GOT and GPT, and could promoted nitrate nitrogen content in leaves and roots. But if nitrate nitrogen content> 50%, it could significantly decreased physiological and metabolism indexes and inhibited the growth of different genotypic rice seedlings. It was more beneficial to improve photosynthetic rate of function leaves, improved the activities of nitrogen metabolism key enzymes, promoted accumulation of osmotic adjustment materials and nitrogen uptake, could full play advantage of promoting fertilizer by proper water stress and promoted the growth in rice of moderate reduce the ammonium/nitrate ratio is 50:50 than 100:0 and normal water condition. In addition, the response extent of different genotypic rice was significant differences under proper water stress. Compared with indica rice and japonica, hybrid indica rice and conventional indica rice, conventional japonica upland rice and conventional japonica rice, the former is much obviously better than the latter of nitrate absorption, the activities of nitrogen metabolism key enzymes, photosynthetic rate, nitrogen absorption and utilization was consistent with drought tolerance of different genotypic rice.4. Effect of status of soil moisture on the physiological characteristics and yield components under different nitrogen forms during grain filling in riceProper soil moisture (Ψsoil=-25 kPa) during grain filling and ammonium/nitrate ratio 50:50, yield significantly increased than ammonium/nitrate ratio 100:0, and could alleviate adverse effects of yield in short of water. Kinds of ammonium/nitrate ratio treatment, panicle length, primary branch number, secondary branch number and spikelet density were all first and then decreased during water stress increased, and the biggest was-25 kPa soil moisture treatment. Effects most influential of secondary branch number on soil moisture. Therefore, proper soil moisture could make sure improve panicle length and keeping suitable primary branch number, combined with suitable ammonium/nitrate ratio 50:50 could increase secondary branch number, efficient leaf area ratio and spikelet density, improve the potentiality of increase yield. Furthermore, soil moisture 0 kPa--25 kPa and proper significantly increased with ammonium/nitrate ratio, benefit to promote redistribution of reserves in stem and sheath, photosynthetic rate, bleeding intensity, anti-aging enzymes activities and nitrogen cumulate during grain filling in rice. But there were not reached significant level compared with ammonium nitrogen and significant level compared with nitrate nitrogen. But when soil moisture (Ψsoil≤-50 kPa), advantage decreased ammonium nitrogen ratio (ammonium/nitrate ratio is 100:0), is more beneficial to relief significantly decreased photosynthetic rate and anti-aging enzymes activities.5. Effect of status of proper soil moisture under different nitrogen forms during grain filling in different genotypic riceEffect treatment factors of yield and yield compositions, influence of different genotypic, nitrogen forms took second place, soil moisture was the least. Two factors toxicity interaction effect, the interaction of different genotypic and nitrogen forms was the biggest one. There was an extremely significantly interaction effect to yield among different genotypic rice, soil moisture and nitrogen forms. Proper soil moisture (Ψsoil≤=-25 kPa) and proper increased nitrate nitrogen ratio (ammonium/nitrate ratio is 50:50), were all beneficial to increase absorb and utilization ammonium and nitrate nitrogen, could relief adverse effect of water stress, significantly promoted increase yield. But could not improve the rate of excessive nitrate nitrogen ratio, because it would inhibited the absorption of ammonium nitrogen, aggravated double stress of water and nitrogen fertilizer, finally lead to yield reduction. Under different water and nitrogen treatments, kinds of rice variety were all manifested as hybrid indica rice> conventional indica rice, conventional japonica rice>conventional japonica upland rice (tillering ability is so poor and effective panicles are less). Furthermore, different nitrogen forms under proper soil moisture in different genotypic rice were significant differences. Under ammonium nitrogen ratio≥50%, compared with indica rice and japonica, hybrid indica rice and conventional indica rice, conventional japonica upland rice and conventional japonica rice, the former is much obviously better than the latter of harvest index, nitrogen absorption and utilization, the activities of nitrogen metabolism key enzymes, photosynthetic rate, material transport in stem-sheath and improve anti-aging enzymes activities. But under proper soil moisture and ammonium nitrogen ratio< 50%, two varieties which have stronger drought tolerance: hybrid indica rice and conventional japonica upland rice have more advantages of the activities of nitrogen metabolism key enzymes and anti-aging enzymes than other rice varieties.