Regulation Mechanism Of Nitrogen Spraying After Anthesis On High Temperature Stress In Spring Wheat

In recent years,with the global warming,extreme weather occurred frequently,especially the high temperature at the filling stage caused premature senescence of wheat,which seriously affected the yield and quality of wheat.Therefore,this experiment simulated post-anthesis high temperature stress of spring wheat and sprayed nitrogen at different post-anthesis stages to study the effect on physiological mechanism of spring wheat.Field experiments were carried out in 2020-2021,and split plot design was adopted.The main plot consisted of 4 foliage-spraying stages of 5,10,15 and 20 days after anthesis,respectively,with no nitrogen application as the control(foliar nitrogen with 2%)urea.The sub-plot was set at 25℃±2 ℃(CK)and 35℃±2℃(HT).By analyzing different periods after high temperature stress and spend spring wheat photosynthetic characteristics and fluorescence characteristics of foliar nitrogen formation key enzymes,antioxidant properties,starch,etc.,the combination of spring wheat leaf transcription and protein group correlation analysis,so as to reveal different periods after spraying nitrogen ease take high temperature cause the mechanism of wheat premature aging,the main results were as follows:1.Nitrogen spraying on the leaf surface at the appropriate post-flowering stage can effectively alleviate the damage caused by high temperature,keep high chlorophyll content in the leaves under high temperature stress,slow down the decline rate of chlorophyll in flag leaves,and then resist the damage caused by high temperature,and improve the light catching ability of wheat.Compared with the natural condition,the chlorophyll A content of 5 d,10 d,15 d,20 d and CK after high temperature treatment decreased by 17.69%,14.13%,13.48%,9.24%,19.90%,respectively.Compared with CK,nitrogen spraying treatment alleviated the premature plant senescence.The photosynthetic performance and fluorescence parameters were the best at 20 days after anthesis.2.High temperature after anthesis intensified membrane lipid peroxidation in flag leaves of wheat,resulting in decreased activities of SOD,POD,CAT and other protective enzymes,and increased malondialdehyde and proline contents.Spraying nitrogen fertilizer on leaves at the optimum stage after anthesis could enhance the activities of SOD,POD and CAT enzymes,and inhibit the production of malondialdehyde and proline.Compared with the natural condition,SOD activity of 5 d,10 d,15 d,20 d and CK after high temperature treatment decreased by 7.02%,5.31%,4.21%,0.87%and 5.87%,respectively.Nitrogen spraying treatment on 10 d,15 d and 20 d after anther treatment alleviated plant premature senescence compared with CK.The effect of nitrogen spraying became better with the later stage of nitrogen spraying,indicating that the effect of nitrogen spraying was the best 20 days after flowering.Nitrogen spraying at this stage was more conducive to increasing the plant’s resistance to adversity and effectively alleviating the damage caused by high temperature.3.High temperature stress accelerated the filling speed and decreased the starch synthesis ability.The total starch content of CK at 5,10,15,20 d after anthesis decreased by 13.21%,11.60%,21.71%,22.08%and 22.54%,respectively.The activities of key enzymes in starch formation(ADPG-PPase,UDPG-PPase,GBSS,SSS and SBE)could be increased by spraying nitrogen fertilizer on leaves at the optimum stage after anther,and the effect was most obvious at 20 d after anther,suggesting that spraying nitrogen fertilizer at high temperature reduced the activity of enzymes.Thus effectively delaying the effects of premature aging of plants.4.Spring wheat flag leaf transcription and protein group sequencing analysis shows that the high temperature stress will directly affect the metabolism of wheat leaf photosynthesis and chlorophyll,the leaf photosynthesis and chlorophyll synthesis genes has obvious influence,among them,promote the photosynthesis of the gene expression of most of the cut,hinder the increase of photosynthesis gene expression;At the same time,the expression of related genes involved in chlorophyll synthesis was down-regulated,and the expression of related genes that accelerated chlorophyll decomposition was up-regulated,which may be the main cause of premature plant senescence.From the perspective of gene expression level,two genes encoding superoxide dismutase were up-regulated.In the whole peroxisome pathway,the up-regulated genes were PXMP2,MPV17,FAR,PIPOC,etc.,while the down-regulated genes were HPCL2,ACOX,PEX10,etc.Nitrogen spraying on leaves after anther can up-regulate the expression of genes in nitrogen compound metabolism,plant hormone signal transduction,glutathione metabolism and other pathways,and strengthen the transport and metabolism of carbohydrate,protein and other processes,thus alleviating the damage of high temperature stress on wheat.5.Post-anthracite high temperature stress can decrease grain number per spike,grain weight per spike,grain number per set spikelets and 1000-grain weight of wheat,and then decrease wheat yield.The 1000-grain weight and yield of wheat were increased by foliar spraying of n fertilizer under natural condition and high temperature stress,and the 1000-grain weight was 15 d>20 d>10 d>5 d>CK and the yield was 20 d>5 d>10 d>15 d>CK under high temperature stress.It is concluded that nitrogen spraying at appropriate stage can effectively increase the filling intensity and prolong the filling time,thus alleviating the premature aging phenomenon caused by high temperature,and significantly increase the 1000-grain weight and yield of wheat.The effect of nitrogen spraying on leaves 20 days after anthesis is the most obvious,which increases the yield by 25.80%compared with the control.In conclusion,spraying n fertilizer after anthesis can effectively improve photosynthetic efficiency and antioxidant capacity of plants,and alleviate the harm of high temperature on premature senescence of wheat.At 20 days after anthesis,nitrogen fertilizer applied to leaves had the best effect,which improved light trapping ability and stress resistance ability of wheat,increased photosynthetic electron transport,photosynthate formation,ATPase and photosystem i/ii activities,and up-regulated the expression of most genes in photosynthesis,MAPK protein kinase,starch and sucrose metabolism.Thus effectively alleviate the phenomenon of premature aging caused by high temperature,and finally achieve the purpose of increasing production and income.