Effect Of Different Water Stress And Nitrogen Forms On Growth And Physiological Characteristics Of Rice

Shortage of water resource has been an critical restraining factor for the development of agriculture and rural economy in China. The production of rice, an important and the water consuming crop, depends mainly on water and nitrogen supply. It is pendent task for agricultural researchers to develop water-saving techniques for rice cultivationwhich, upon application, may lead to changes in microenvironments. Subsequently, soil nitrate nitrogen increases significantly and becomes the most important nitrogen source. However, there is a lack of systematic research concerning the influence of nitrogenforms on rice physiological growth in water stress conditions. This paper tries to uncover this enigma and thus provide theoretical instructions for efficient fertilization of water-saving cultivated rice.In this paper, rice cultivar including ShanYou 63, WuYuJing 3 were cultivated under different water stress condition simulated using PEG. Indices for rice morphology, physiology, growth and yields were determined. These include, (1) Germination ratio and some crucial drought resistance indices includingmoisture content, cell membrane penetrability and anti-oxidase, under water stress conditions. (2) Biomass, root morphological indices, root activity and bleeding sap amount of rice seedlings. (3) Index of NO3-and NH4+-N absorption. (4) Effects of interval water stress on characteristic parameters of NH4+ and NO3- adsorption. (5) Iinfluence of water and nitrogen treatment on water uptake was analyzed by root killing and treatment of HgCl2(0.5mol·L-1). (6) Cell membrane penetrability, potential and other properties of cell membrane of rice root. (7) The influence of nitrogen supply on dry farming rice yield and nutrient uptake in field experiments. (8) The ferrous film on root surface in soil-sand mixed pot culture experiment.The results showed that, (1) Water stress affected radicle and germ differently. Slight water stress enhanced the growth of rice radicle while reduced that of rice germs. Compared with normal water supply treatments, K+content, soluble sugar, sucrose and proline in two rice varieties increased under the treatment of PEG(50g·L-1). Under water stress conditions, the activity of SOD, POD, and CAT of WuYuJing 3 were higher. Malonic-aldehyde content in rice was increased by 16.64%. The activity of SOD, POD, and CAT of ShanYou 63 increased as well but no effects of water stress was found on cell membrane penetrability and the malonic-aldehyde content of Shanyou 63. (2) Slight water stress enhanced the growth of rice roots. Total root length, surface area and volume were increased, while average root diameter decreased. The threshold of water stress of japonica rice was 100g·L-1 PEG and between 50~100 g·L-1 PEG of hsien rice. Under normal water conditions, treatment of NH4+-N/NO3--N (5/5) enhanced the root volume of all rice varieties. Root surface areas of YangJing 9538 and YangDao 6 were enhanced, and root diameter of LianJiaJing 1, LiangYouPei 9 and YangJing 9538 were enhanced. Root surface area and volume of all rice varieties increased with the decrease of NH4+-N/NO3--N after water stress, signifying equivalent ammonium supply was liable to enhance rice root diameters.(3) Under condition of normal water supply, application of NH4+-N increased shoot mass accumulation while. NO3--N was benificial to total adsorption area and mass accumulation of rice roots. The active adsorption area and active adsorption area ratio reached the climax with NH4+-N/NO3--N at a ratio of 5/5. Best growth of rice shoot was obtained at NH4+-N/NO3--N(5/5) under water stress. NO3--N absorption increased fresh and dry weight and average diameter. Total adsorption area andactive adsorption area of rice roots increased with the incease of NO3--N ratio. Bleeding sap amount decreased in all water stress treatment. The highest bleeding sap amount was detected in the treatments with NH4+-N/NO3--N at a ration of 5/5 under normal water condition and NH4+-N/NO3--N(9/1) under water stress.(4) The electrical conductivity of rice seedling leaf extract increased with the decrement of NH4+-N/NO3--N under condition of normal water supply, while that decreased with the decrement of NH4+-N/NO3--N under water stress. The extract electrical conductivity of NH4+-N/NO3--N 25/75 was lea than that of normal water culture. Water stress led to the reduction of relative water content of high NH4+-N/NO3--N treatments and the rise of critical moisture saturation deficit, while the influence of low NH4+-N/NO3--N treatments was insignificant. Low NH4+-N/NO3--N generally alleviated the cacoethic effect of water stress on rice water physiology.(5) The existence of NH4+-N restrained the NO3--N uptake of rice seedling for ShanYou 63, but enhanced the NO3--N uptake for WuYuJing 3. The results were different while the rice be culvitaed in water stress condition for a few days. The existence of NH4+-N enhanced the NO3--N uptake for ShanYou 63, restrained the NO3--N uptake for WuYuJing 3. More NH4+-N were absorbed with the supply of NO3--N.The existence of NO3--N enhanced the uptake of NH4+-N for rice. When the consistence of NO3--N was less than that of NH4+-N, the uptake of NO3--N was restrained by NH4+-N. When the consistence of NO3--N was more than that of NH4+-N, the uptake of NO3--N was promoted by NH4+-N.(6) The nitrogen forms affected the yield, growth and nutrition uptake of rice. The nitrogen treatment of NH4+-N/NO3--N(5/5) enhanced the content of chlorophyll and photosynthesis efficiency of rice. Finally, the biological and economic yield of rice were increased. The treatment of supply higher proportion of NO3--N enhanced the content of soluble sugar and sucrose in rice, increased the pH of soil, while the availability of Fe, Mn, Cu and Zn were decreased.(7) For root killing treatment, under the non-water stress condition, the uptake of water under NH4+-N/NO3--N 9/1, 5/5 and 1/9 treatments were decreased by 26.5%, 24.1% and 36.3%, while 30.6%, 23.9% and 21.0% under water stress condition. For HgCl2 treatment, under the non-water stress condition, the uptake of water under NH4+-N/NO3--N 9/1, 5/5 and 1/9 treatments were decreased by 47.1%, 46.3% and 31.8%, while 46.6%, 42.4% and 23.5% under water stress condition. The treatment of water stress and nitrogen forms influenced water uptake, affected stomatal conductance and photosynthetic rate of rice.(8) Under non-water stress condition, the accumulation of Fe and Mn in leaves for YangDao 6 increased with the descending of NH4+-N/NO3--N. Under water stress condition, the consistence of Mn and Zn of leaves in Wu YuJing 3 was decreased, while the consistence of Fe were increased. Contray to water stress condition, there were more ferrous film existed on the root surface of rice under non-water stress condition.(9) The electrical conductivity of leaves and roots in rice was highest at the ratio of NH4+-N/NO3--N(1/9) under non-water stress condition, while the electrical conductivity of leaves and roots in rice was highest at the ratio of NH4+-N/NO3--N(9/1) under water stress condition. The supply of NH4+-N decreased the pH of nutrient solution, while the pH increased with the supply of NO3--N. Compared with the non-water stress condition, the cell membrane potential in NH4+-N/NO3--N(5/5) treatment was a little higher than that under water stress condition.