Effects Of Different Cultivars And Cultivations On Leaf Senescence And C/N Of Wheat

Leaf is the main place for carbon fixation and nitrogen assimilation in plants,and premature senescence of leaves may lead to poor crop morphogenesis,decline in yield,and even death.Therefore,it is important to explore the internal mechanism and influencing factors of leaf senescence in the regulation of leaf senescence.Nitrogen is one of the important factors that affect leaf senescence.Nitrogen deficiency induces and accelerates leaf senescence,but the mechanism of leaf senescence induced by nitrogen deficiency is not clear.Part of the research indicated that leaf senescence was due to low nitrogen levels in cells.And studies have shown that carbon and nitrogen balance was harmed at low nitrogen stress,so that the accumulation of carbon and carbon nitrogen imbalance is also involved.in leaf senescence induced by nitrogen deficiency.In view of this,we designed 2 experiments:(1)The four wheat varieties of different nitrogen deficiency sensitiveHengguan 35,Xinong 979,Zhoumai 24 and Yunhan 618 was exspent under low nitrogen stress to explore the relationship between the leaf senescence and nitrogen level,non structural carbohydrates,carbon and nitrogen;(2)According to the research of senescence change of flag leaf in the condition of different fertilizer during grain filling stage,to revelant the relationship between the changes of structural carbohydrates,carbon nitrogen balance and yield.The main results was as follows:(1)The net photosynthetic rate,chlorophyll content and Fv/Fm of four wheat varieties were significantly decreased under nitrogen stresst,which showed that nitrogen-deficiency induced and accelerated the wheat leaf senescence.The degree of leaf senescence of the nitrogen-deficiency sensitive wheat cultivars were significantly deep than the nitrogen-deficiency tolerant wheat cultivars.The leaf nitrogen content of all cultivars was plummeted,while the non-structural carbon carbohydrates content was largely increased.Therefore,the C/N ratio was increased after the nitrogen-deficiency treatment.Further analysis showed those C/N ratios are highly correlated with the degree of the leaf senescence.The results indicated that the carbon/nitrogen balance are involved in the regulation of nitrogen-deficiency-induced leaf senescence,and the wheat cultivars with slightly leaf senescence had stronger capacity to maintain the balance of nitrogen and carbohydrates metabolism.(2)The chlorophyll content of flag leaves decreased gradually with the advance of grain filling process in the field.The lower the amount of nitrogen,the lower the chlorophyll content and the faster the rate of decrease,indicating that low nitrogen induced and accelerated the senescence of leaves.With the process of grain filling,nitrogen content of flag leaf decreased,non structural carbohydrate(soluble sugar and starch)accumulation increased gradually,the C/N increased,and the amount of nitrogen was lower,and the higher the C/N,carbon and nitrogen sooner than the rising time.After comprehensive analysis,it was found that the senescence degree of flag leaves in wheat was negatively correlated with C/N.Water was also found to affect carbon and nitrogen balance in wheat leaves,and no significant difference in nitrogen levels between irrigation and non irrigation.However,the ratio of carbon to nitrogen in flag leaf leaves treated with irrigation was significantly higher than that without irrigationunder low nitrogen levels(N0 and N60),and the earlier the leaf senescence time during the grain filling process.Under high nitrogen,compared with non irrigation,irrigation decreased the C/N of leaves,and delayed the increase of C / N ratio.The results showed that fertilization and irrigation affected the senescence of leaves at grain filling stage,as well as the C/N,and leaf senescence was positively related to C / N ratio.(3)Further analysis of yield and yield components revealed thatirrigation significantly reduced grain yield compared to non irrigationat low nitrogen levels(N0 and N60).In the middle nitrogen level(N120),irrigation significantly increased grain yield,and irrigation had no significant effect on grain yieldunder high nitrogen(N180)level.The analysis showed that irrigation of low nitrogen level resulted in a significant reduction in grain weight,panicle number and grain number per spike,resulting in a significant decrease in yield.In the high nitrogen level,irrigation significantly reduced the 1000 grain weight of N180,but the number of panicles increased significantly,and the two had a common effect,which had no significant effect on yield.The flag leaf during grain filling of nitrogen,carbon and C/N further analysis indicated that irrigation increased in flag leaf during grain filling ratio of carbon and nitrogen under low nitrogen level,thus accelerating the leaf senescence,and the yield decreased,whilemaintain the suitable carbon and nitrogen under the middle nitrogen levelat late grain filling stage to delaied leaf senescence and increased yield.The results showed that the sensitivity of winter wheat varieties to nitrogen deficiency and senescence was related to their C/N,and the greater theC/N,the more serious the degree of senescence was.Under field conditions,leaf senescence had intimate connection with C/N.Nitrogen level and irrigation had effects on C/N,thereby regulating leaf senescence,and furtherinfluenced the production.