| Dissolved oxygen(DO)plays an important role in nitrogen cycling in paddy fields and the growth and development of rice.To further study the effects of DO on nitrogen transformation in paddy field and nitrogen metabolism in rice plants is of great significance for reducing nitrogen loss in paddy field and improving nitrogen utilization efficiency of rice.In this research,two experiments were carried out:(1)three rice cultivars with different ecotypes,Zhongzheyou 1(lowland rice),IR45765-3B(deep water rice)and Zhonghan 221(upland rice),were used to study the effects of aeration methods on rice photosynthetic characteristics,yield formation,as well as nitrogen transformation in paddy soil,rice plant nitrogen uptake and utilization.There were four oxygen enrichment treatments in this study,i.e.calcium peroxide application,micro-bubble aerated water irrigation,topsoil moist irrigation and water-logging(control).(2): Zhongzheyou 1,IR45765-3B and Zhonghan 221 were used as plant material,and five DO concentrations(1 mg/L,3 mg/L,5.5 mg/L,7.5 mg/L and natural growth)were set to explore the influence of different DO concentrations on the changes of contents of different nitrogen forms,as well as root growth,nitrogen uptake and utilization of rice under the condition of water cultivation.The main results in this study were as follows:1.Calcium peroxide application and micro-bubble aerated water irrigation increased the leaf SPAD value,leaf area index,net photosynthetic rate,transpiration rate,stomatal conductance and dry matter accumulation of the three rice varieties during the main growth stages,and enhanced the effective panicles numbers and seed setting rate significantly.Compared with the control,the SPAD value,leaf area index,photosynthetic parameters and dry matter weight of the three varieties were decreased in topsoil moist irrigation,and the seed setting rate was also significantly lower,but the water use efficiency of leaves was increased.At full ripe stage,the grain yields of Zhongzheyou 1,IR45765-3B and Zhonghan 221 were increased by 22.38%,18.27% and 18.17%,respectively,in calcium peroxide application as compared to the control,and increased by 13.89%,10.67% and 8.85%,respectively,in micro-bubble aerated water irrigation.However,it was 5.86%,8.19% and 6.16%,respectively,lower than that of control in topsoil moist irrigation,with considerable differences between treatments.2.The aeration methods significantly increased soil redox potential and improved the soil oxygen environment.The soil nitrification intensity and urease activity of oxygen enrichment treatments were significantly higher than that of water-logging at tillering stage and full heading stage.In contrast,the denitrification intensity of oxygen enrichment treatments was remarkably lower than that of water-logging.The oxygen enrichment treatments could affect the uptake of rice nitrogen differently.Nitrogen accumulation amounts of the three rice cultivars were considerably higher in calcium peroxide application and micro-bubble aerated water irrigation than in control at jointing,full heading and full ripe stage,while it was substantially lower than that of control in topsoil moist irrigation.At full ripe stages,total N accumulation amounts of Zhongzheyou 1,IR45765-3B and Zhonghan 221 were increased by 21.2%,13.2% and 17.0%,respectively,in calcium peroxide application as compared with control,and increased by 14.3%,6.9% and 9.1%,respectively,in micro-bubble aerated water irrigation.Compared with control,the harvest index in calcium peroxide application and micro-bubble aerated water irrigation was greatly increased.But their nitrogen grain production efficiency had no significant difference compared with control.However,nitrogen biomass production efficiency and nitrogen grain production efficiency in topsoil moist irrigation were considerably higher than that in control.3.Under the condition of hydroponics experiment,the decrease rate of total nitrogen content in nutrient solution decreased with the increase of DO concentration,the change trend of ammonium salt content was opposite to total nitrogen content under different DO concentrations.At the same determination time,the nitrate content increased with the increase of DO concentration.Nitrite content was extremely low and was unstable in nutrient solution.Three rice varieties could form obvious lysigenous air cavity in 1 mg/L DO.There was still obvious aerenchyma in Zhongzheyou 1,while parenchyma cells of IR45765-3B and Zhonghan 221 were less lysis than the former in 3 mg/L DO and natural growth.The roots of all rice varieties did not form aerenchyma or air cavity formation was rarely in 5.5 mg/L DO and 7.5 mg/L DO.The root activity of 3 mg/L DO was higher than that of natural growth,while the root activities of 1 mg/L DO and 7.5 mg/L DO were lower than natural growth,and the root activity were different between varieties.The activity of root system at the same DO concentration was Zhongzheyou 1 > Zhonghan221 > IR45765-3B at tillering stage.The amount of dry matter and yield of three rice varieties were 3 mg/L DO > natural growth > 1 mg/L DO > 5.5 mg/L DO > 7.5 mg/L DO under different DO concentrations at full ripe stage.Grain yield of three rice varieties was increased by 1.0%-12.9% in 3 mg/L DO as compared with natural growth,and decreased by 1.7%-18.9%,7.6%-23.1% and 18.8%-57.0%,respectively,in 1 mg/L DO,5.5 mg/L DO and 7.5 mg/L DO.4.Under the condition of hydroponics,the activities of glutamine synthetase,glutamate dehydrogenase,aspartate aminotransferase and alanine aminotransferase were different in different growth stages and cultivars,but there was no obvious regularity.The nitrogen content of three rice varieties were decreased gradually with the extension of growth period under different DO concentrations.Nitrogen content of rice plants decreased gradually with the increase of DO concentration at jointing stage,the performance of nitrogen content among treatments showed the opposite at full heading stage and full ripe stage as compared with jointing stage.Compared with natural growth,the nitrogen accumulation of three varieties increased under 3 mg/L DO during different growth period.The nitrogen uptake of rice was decreased at 5.5 mg/L DO and 7.5 mg/L DO,and the proportion of nitrogen accumulation in later stage of rice growth was increased.At full ripe stage,nitrogen accumulation of three rice varieties was increased by 2.3%-7.3% in 3 mg/L DO as compared with natural growth,and decreased by 0.7%-3.6%,3.6%-8.5% and 15.0%-27.1%,respectively,in 1 mg/L DO,5.5 mg/L DO and 7.5 mg/L DO.Compared with natural growth,3 mg/L DO improved the harvest index,nitrogen harvest index and nitrogen use efficiency for grain production of three rice varieties,but the above indicators were declined in other DO concentrations.In all treatments,the nitrogen use efficiency for biomass production was the highest in 1 mg/L DO. |
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