Effect Mechanism Of Rice Rhizosphere Oxygen Concentration On Root Morphology And Nitrogen Metabolism At Tillering Stage

Rice root is not only the absorption organ(water, nutrients), but also an important place which could synthesis some endogenous hormones, and its development is closely related to the morphology development and yield formation of the above ground organs.Rice is more sensitive to oxygen concentration at tillering stage, and the rhizosphere oxygen concentration affect root growth is larger, and at the same time root development,root type construction at tillering stage is a key period of root type during the whole growth period. In recent years, the rice variety of nitrogen fertilizer tolerance is increasing, while the utilization of nitrogen fertilizer is declining. The previous study found that rice rhizosphere oxygen concentration affect root morphology, growth and nitrogen absorption,but the mechanism of rice rhizosphere oxygen concentration affect the root morphology,nitrogen metabolism at tillering stage have not been involved. Thus, in this experiment intends to from morphology, anatomy and enzymology to reveal the effect mechanism of root morphogenesis and nitrogen metabolism at tillering stage, the rice plants with different oxygen treatment were subjected using hydroponics and soil culture to(1) rice rhizosphere oxygen concentration affect root morphology, physiological characteristics and micro morphological structure at tillering stage;(2) low oxygen stress affect rice root function and nitrogen metabolism at tillering stage;(3) different nitrogen and oxygen environment affect rice growth, agronomic shape and nitrogen metabolism at tillering stage;(4)different rhizosphere oxygen environment affect the change of soil environment,absorption and utilization of nitrogen in rice. The results indicated that:1. Compared to the control(oxygen concentration was 1.0 to 2.0 mg/L), under the medium oxygen concentrations(2.5 to 3.5 mg/L) treatment, the root, shoot and total dry weights increased, the root tip numbers, length and surface area, the proportion of fine roots also increased and the coarse root decreased at tilleing stage, which contributes to nutrient uptake, the total absorption and accumulation of N, P, K, Mn, Mg and Ca increased. The root, shoot and total dry weights decreased under high oxygen concentrations treatment(>6.0 mg/L). Low oxygen concentrations(0~1 mg/L)induced the total absorption and accumulation of Fe, Cu and Zn increased, induced root aerenchyma formation and increased root porosity. Low and high oxygen stress both damaged apical cell ultrastructure, plasmolysis or cell wall thicken appeared, reduced the number of organelles, increased the number of vacuoles, the volume of vacuoles became larger, and even vacuolation, which accelerated cell aging. Damaged the cell membrane permeability,causing electrolyte leakage so that conductivity increased, the root soluble protein content,root activity and respiration rate were decreased when compared with the control. Under medium oxygen concentrations treatment, the cell structure was intact, organelles increased, nucleus significantly, the chromatin was rich and multiple inclusions, rootrelative conductivity changed little, the cell membrane was not damaged, organelles of root tip was rich and the physiological activity was strong, so root soluble protein content,root activity and respiration rate were increased when compared with the control.2. Short low oxygen stress inhibited the occurrence of tillers and biomass accumulation of rice at tillering stage. The effect of low oxygen stress on rice root respiratory intensity and activity were inhibited-promoted-inhibited. The activity of nitrate reductase(NR) in root was promoted under low oxygen stress. The activity of glutamine synthase(GS) in root was promoted from 0 to 6 days and was inhibited from 9to 12 days under low oxygen stress. Low oxygen stress affect the activity of glutamate dehydrogenase(NADH-GDH) was relevant to the rice variety, it was promoted-inhibited of Xiushui 09, and it was inhibited-promoted-inhibited of Chunyou 84. At the end of treatment, soluble protein content was decreased and proline content was increased. It was concluded that rice are probably by improving respiration consumption and changing the metabolic pathway to alleviate low oxygen stress injury, and to maintain their survival under the condition of low oxygen stress at tillering stage.3. The amount of nitrate uptake was mainly concentrated in rice roots at tillering stage.Under the same oxygen treatment, the amount of ammonium uptake was far greater than that of nitrate, and the amount of ammonium in leaf was greater than that in root. Medium oxygen treatment induced the absorption and accumulation of nitrate and ammonium nitrogen, hypoxia inhibited the absorption and accumulation of nitrate and ammonium nitrogen. Under the same oxygen treatment, with pure ammonium nutrition, Chlorophyll a,b and total chlorophyll content, NR and GS activity, nitrogen uptake and accumulation of nitrate were higher than those of pure nitrate nutrition. When with different nitrogen sources in hydroponics, the rhizosphere oxygen concentrations had different effect on root morphology of rice at tilering stage. Pure nitrate culture and rhizosphere oxygen concentrations both influenced the root length, total absorption area and total root tip number of rice seedlings. When pure ammonium culture, the difference of root morphology between different rhizosphere oxygen concentrations was not great.4. There was no significant effect of rice dry matter accumulation under different oxygen environment of soil. Soil WD(wet and dry) and logging treatment increased the NR activity of leaves, promoted the absorption and accumulation of nitrogen, increased the number of effective panicle, grains per panicle, 1000 grain weight, single vascular bundle area of root basal part of stem and panicle neck at heading stage. There were significant or extremely significant positive correlation among the vascular bundle number of the stem basal part and panicle neck, single vascular bundle area, and the yield components.5. Different rhizosphere oxygen treatment of soil would affect the soil environment.The effect of logging treatment on soil pH value was continuous, and the pH value of soil increased with the growth of rice. WD and logging treatment increased soil respirationintensity at tillering and heading stage, increased nitrification intensity and ammonia oxidizing bacteria number at heading and maturity stage, at this time, the nitrification intensity was positively correlated with the nitrogen absorption. It was concluded that through improved the oxygen content of soil at the late growth stage of rice to improve nitrogen absorption and utilization rate.