Nitrogen Granular Fertilizer Alleviating Rice Early Grain Filling Stage Heat Stress And Its Physiological Mechanism

Rice is an important food crop in our country.Heat disaster occurred frequently in rice grain filling stage because of the global warming,which would bring a serious threat to rice production in the midstream and downstream of Yangtze River.Therefore,it has an important meaning to research the influence of heat stress on rice growth and the damage mechanism,and put forward the corresponding mitigation technology to reduce heat loss.In terms of the corresponding measures,in addition to breeding resistant varieties,the reasonable cultivation measure is also an important way.Nitrogen management is one of the most important cultural practices,and delaying the application of Nitrogen has greatly reduced the heat loss of rice.Two major cultivars,Wuyunjing24 and Ningjing3 were used in this study and under three nitrogen fertilizer levels,low nitrogen level(LN,Og nitrogen per pot),medium nitrogen level(MN,0.8 g nitrogen per pot),and high nitrogen level(HN,1.6 g nitrogen per pot)were established,to provide protection measures for the production of rice for global warming.The main findings are as follows:1.The temperature of rice panicle and leaf significantly rose up under heat stress.Application of nitrogen fertilizer significantly lowered leaf and panicle temperature,HN treatment is better than MN.Nitrogen granular fertilizer greatly improved the flag leaf net photosynthetic rate,stomatal conductance and intercellular CO2 concentration,and it is also one reason for the decrease of leaf and panicle temperature after application of nitrogen fertilizer.Superoxide dismutase(SOD),peroxidase(POD),malondialdehyde(MDA)content significantly increased in rice leaves under high temperature stress.After fertilizing,rice leaves could maintain high SOD,POD activity,but reduced the accumulation of MDA,and it alleviated the damage of membrane lipid.High temperature stress significantly increased rice soluble protein content,and the non-structural carbohydrates(NSC)content was reduced.Soluble protein content significantly increased,and NSC content was reduced.2.The SPAD value of rice flag leaves significantly decreased under high temperature stress.Application of nitrogen fertilizer increased the relative value of leaf SPAD.Nitrate reductase(NR),glutamine synthetase(GS)were inhibited in rice leaves under high temperature stress,and the longer the stress continued,the enzyme activity reduced more obvious.Nitrogen Granular fertilizer administration significantly increased NR,GS activity,and activated rice leaf nitrogen metabolism.High temperature stress in rice leaves significantly increased amino acid contents,but with prolonged stress time,the amino acid content in leaves showed no obvious rising trend.Amino acids in rice leaves could provide sufficient nitrogen for the synthesis of various types of enzymes,and it played a regulatory role in rice stress tolerance mechanisms.Nitrogen Granular fertilizer administration could significantly increase amino acid contents in rice leaves,and nitrogen metabolism was more active under high temperature stress,so rice stress tolerance was improved.3.Heat Stress significantly reduced the rice yield at grain filling stage,which mainly in thousand seed weight and seed setting rate decreased.Application of nitrogen granular fertilizer contributed to relief of the effects of high temperature on grain production.Our results showed that high temperature reduced the seed-setting rate and 1000-grain weight of rice.While the application of nitrogen granular fertilizer can significantly increase the rice 1000-grain weight and make up for a loss of rice final yield under heat stress.The results showed that at the same temperature,especially under high temperature,compared with the LN,the MN and HN significantly increased grain yield,especially at HN.Ningjing3 was susceptible to high temperature stress,and its grain yield decreased greater.4.Early grain filling stage under high temperature stress on rice quality overall performance deterioration.Milling quality,the high temperature stress reduced the rice brown rice rate,milled rice rate,head milled rice rate.Nitrogen fertilizer application significantly increased the brown rice rate,milled rice rate and head milled rice rate,HN treatment is better than MN;Appearance quality,the high temperature stress significantly increased chalkiness occurrence rate and chalky area,but lowered the green rice rate.Nitrogen fertilizer application under high temperature decreased Chalkiness Occurrence rate and chalkiness area,but increased the rate of green rice Cooking and eating quality,the high temperature stress reduced the total starch and amylose content.Nitrogen Granular fertilizer administration also reduces the total starch and amylose content of rice,it had unfavorable effects on rice cooking and eating quality;Nutritional quality,the high temperature on grain filling stage contributed to the accumulation of total protein,significantly increased rice albumin,globulin and glutelin content,reduced prolamin content.Each amino acid composition of rice under high temperature treatment significantly increased,which improved the nutritional quality of rice.Nitrogen Granular fertilizer administration also significantly increased the total amount of rice amino acids,but not changed the ratio of amino acid composition.