Studies On The Effects Of Nitrogen Forms And Water Station On Water Physiology And Nitrogen Metabolization Of Rice(Oryza Sativa L) Seedlings

Water supply and nitrogen nutrition are the two major restrictions for plant growth and development. At present, developing water-saving.rice cultivations, such as covering with plastic film and straw mulching, is becoming a hot topic of agricultural production research. There are two major differences between traditional cultivation and non-flooded conditions:(1) rice plants are frequently suffered from water stress in non-flooded condition;(2) nitrogen form is transferred from ammonium to nitrate or the mixture of ammonium and nitrate. Therefore, it is important to study the influence of water stress and nitrogen forms on plant growth, water relations, photosynthesis, nitrogen abosorption and metabolization.In order to study the effects of different nitrogen forms and water stress on plant growth, water relations, photosynthesis, nitrogen absorption and utilization, hydroponic experiments supplied with different N forms and water stress simulated by adding10%(M/V) polyethylene glycol6000were conducted, four rice genotypic varieties (Shanyou63, Yangdao6,86you8and Wuyunjing7) were utilized in the experiments, which can illustrate the response of different genotypic rice plants under the water stress condition, and pro vied varietal reference for conductions in different region with rice water-saving cultivation. The results obtained are as follows:1. Compared with non-water stress condition, water stress significantly stimulated root growth in both N forms, and the stimulation was higher in nitrate nutrition. Of indica rice plants, water stress had no negative effects on shoot biomass and tillers in ammonium nutrition, while significantly decreased them in nitrate nutrition. Of japonica rice plants, water stress significantly decreased shoot biomass and tillers in both N forms. Under water stress, shoot biomass of japonica rice plants was higher in ammonium nutrition than in nitrate nutrition. Regardless of water stress, whole plant biomass was higher in ammonium nutrition than in nitrate nutrition. 2. Under water stress, root activity, absorption area and water uptake ability were higher in ammonium nutrition than in nitrate nutrition. Regardless of water status, water uptake and transport in ammonium nutrition were mainly through cell-cell passway; in nitrate nutrition, they were mainly through cell-cell pathway under non-water stress and throught apoplastic pathway under water stress condition.3. Water stress increased root aerenchyma formation, especially in nitrate nutrition. Water stress decreased root root hydraulic conductivity and xylem sap flow rate in nitrate nutrition, while had no negative effects in ammonium nutrition. The formation of aerenchyma in nitrate nutrition restrained radial water transport in the root cylinder and, as a result, decreased water uptake ability. Water transport occurred mainly through Hg-sensitive water channels in ammonium-supplied rice roots.4. Regardless of water status, net photosynthetic rate (Pn) was higher in ammonium nutrition than in nitrate nutrition. Water stress significantly decreased total leaf areas, new expanded leaf area and chlorophy content (SPAD value) in nitrate nutrition, while had no negative effects in ammonium nutrition. Maintenance of relative high photosynthesis will benefit in supplying more assimilates.5. Under non-water stress condition, leaf NR activity is significantly higher in nitrate nutrition than in ammonium nutrition. Water stress significantly decreased NR activity in nitrate nutrition, while had no negative effect in ammonium nutrition. Compared with non-water stress, nitrate assimilation ability was decreased in nitrate nutrition, while it was not decreased in ammonium nutrition.6. Water stress decreased leaf, stem and root water content in both N forms, especially in leaves which indicated that leaves were the most sensitive part to water stress. In all conditions, organic osmoticum (proline, free amino acid and soluble sugar) of different parts were leaves> shoot> root. Under water stress condition, the organic osmoticum contents were significantly higher in ammonium nutrition than in nitrate nutrition, whereas inorganic osmoticum contents (calcium ion and magnesium ion) have no abvious effect in nitrate and ammonium nutrition. It showed that organic osmoticums may participated in ammonium nutrition, while inorganic osmoticum contents may not participate in osmotic regulating of rice growth.7. Under water stress, the shoot biomass of rice plants were significantly decreased in nitrate supplied sections, especially in conditions where the two part of roots are both supplied with nitrate nutrition. Regardless of water stress, supplying ammonium nutrition in either or both parts is benefit for maintaining or increasing leaf chlorophy content and net photosynthetic rate. Water uptake ability was negative related to aerenchyma formation in nitrate supplied section, while there was no close relationship in ammonium supplied section. It showed that, differences in water uptake ability between the two N forms were may derived from response of root to environment.