Effects Of High Temperature At Different Growth Stages On Rice Growth And Physiological Characteristics Under Straw Combined With Nitrogen Reduction Measures

The intensification of greenhouse effect and continuous environmental pollution lead to frequent extreme weather,which seriously affects the growth and development of rice.In order to reduce environmental pollution and the use of chemical fertilizer,the country has vigorously promoted straw returning and nitrogen reduction in agricultural production.The current research results show that there are relatively few studies on the effect of straw combined with nitrogen reduction treatment on rice.In order to explore the mechanism of influence of high temperature on the growth and physiological characteristics of rice under straw returning and reduced nitrogen application,rice variety Nanjing 9108 was selected in this experiment,and the following treatments were set:conventional fertilization(CF),conventional nitrogen reduction 20%(CDF),straw+conventional fertilization(SF),straw+conventional nitrogen reduction 20%(SDF).At heading stage and filling stage,they were treated at normal temperature(NT,control)and high temperature(HT,more than normal temperature+5℃).The temperature treatment time was 7 days.The effects of high temperature at different growth stages on the growth,physiological characteristics and quality of rice under straw combined with nitrogen reduction measures were analyzed in order to provide theoretical and practical basis for the safe production of rice under climate change.The main results were as follows:1.High temperature decreased rice yield,and the yield decreased most under high temperature treatment at heading stage.Straw treatment can alleviate the effect of high temperature on yield.At high temperature at heading stage,the actual yield of SDF increased by 28.06%compared with that of CDF.SF increased by 12.04%compared with CF at high temperature during filling stage.Nitrogen reduction by 20%reduced panicle number and actual yield,but increased seed setting rate.Under high temperature at heading stage,the seed setting rate of CDF treatment increased by 6.43 percentage points compared with CF treatment.High temperature,nitrogen reduction treatment,straw combined with nitrogen reduction treatment reduced the aboveground dry matter accumulation.Under high temperature treatment at filling stage,CDF treatment decreased by 14.33%and SDF decreased by 9.30%compared with CF treatment at maturity stage.2.High temperature and straw addition were beneficial to increase the leaf area of rice upper three leaves.SPAD value at high temperature was higher than that at normal temperature,straw treatment increased SPAD value of leaves,but nitrogen reduction treatment was opposite.Under high temperature at heading stage,SF treatment increased 4.12%-16.44%compared with CF treatment,while CDF treatment decreased 2.81%-16.20%compared with CF treatment.3.At high temperature,nitrogen,phosphorus and potassium contents in stem and leaf were increased compared with that at normal temperature,and high temperature had more obvious effect on nutrient contents in various organs at heading stage.Nitrogen reduction treatment and straw combined with nitrogen reduction treatment reduced the nitrogen content of rice organs.High temperature decreased the total nitrogen uptake,phosphorus uptake and potassium uptake of aboveground parts.The nitrogen absorption under different treatments was generally in the order of SF>CF>SDF>CDF.Under high temperature at heading stage,the amplification of SF compared with CF was 7.49%-12.39%,and that of SF compared with SDF was 14.27%20.55%.With the increase of temperature,the proportion of nitrogen,phosphorus and potassium in panicle decreased significantly.Straw treatment and straw combined with nitrogen reduction treatment could increase the proportion of nitrogen and phosphorus in panicle.Under high temperature at heading stage,the proportion of nitrogen in panicle treated with SDF and SF increased by 5.15 and 3.16 percentage points compared with CF treatment,respectively.The distribution of phosphorus increased by 3.25 percentage points and 5.89 percentage points respectively.4.The enzyme activities related to nitrogen metabolism of leaves decreased with increasing temperature,and the decrease rate was the largest under high temperature treatment at heading stage.The enzyme activities of GS and GDH were decreased by straw combined with nitrogen reduction.At normal temperature,the overall activity of GOGAT enzyme was SF>SDF,and at maturity,SF increased by 13.86%compared with SDF.5.SDF treatment had the best processing quality at normal temperature,while SDF treatment had the worst processing quality at high temperature.The high temperature reduced the consistency of rice glue and amylose content.Compared with normal temperature,the consistency of rice glue treated with CF at high temperature at heading stage decreased by 7.87%,and the amylose content decreased by 3 percentage points.Under high temperature,the disintegration value and pulping temperature of rice increased,while the other RVA characteristic values decreased.Compared with normal temperature,CF treatment at high temperature at heading stage decreased by 6.27%～46.67%.Under normal temperature and heading stage,the characteristic values showed CF>SF in general,but the opposite was true under high temperature at filling stage.6.High temperature and straw treatment increased the number of cavities in grains.The crystallinity of SDF treatment at normal temperature was the highest,and that of CF treatment at high temperature at heading stage was the highest.With the increase of temperature,the enthalpy value,peak temperature,initial temperature,end temperature and gelatinization range showed an increasing trend,while the peak index showed a decreasing trend.Except for the peak value index,CF>CDF>SF>SDF was the general pattern under different temperature treatments,and the increase of CF under normal temperature was 3.30%-23.00%compared with SDF treatment.The above results showed that high temperature could significantly affect the growth and physiological characteristics of rice,and the effect of high temperature was more obvious at heading stage.In general,straw treatment could alleviate the effect of high temperature on rice yield,and straw treatment combined with straw nitrogen reduction treatment could facilitate the transfer of nutrient elements to ear and improve the proportion of nutrient elements in ear.From the perspective of climate warming countermeasures,appropriate straw treatment and straw combined with nitrogen reduction treatment can be selected to resist the harm caused by high temperature.