Effects Of Nitrogen Addition Rate On The Relationships Between Asynchrony Of Soil Microbial Populations And Yield In Rice-wheat Rotation System

Optimal nitrogen（N）management and beneficial soil microbial communities play important roles in promoting grain yield.This study was based on the long-term（since 2010）field experiment of rice-wheat rotation with gradient N inputs at the Rugao Agricultural Science Research Institute in Jiangsu Province.The gradient of N addition rate in this rice-wheat rotation was set as:0,140,280,470 and 660 kg·hm^-2.The gradient of N addition rate in wheat season was set as:0,50,100,200 and 300 kg·hm^-2,and the gradient of N addition rate in rice period was set as:0,90,180,270 and 360 kg·hm^-2.In this study,soil samples were collected at before wheat planting,jointing,botting,flowering and maturing stages in wheat season,and before rice planting,max-tillering,shooting,flowering and maturing stages in rice season,to explore the response of soil microbial communities to N addition during key growing stage in rice-wheat rotation using high-throughput sequencing and investigate the effects of N addition on relationships between asynchrony of soil microbial populations and yield.The main results obtained are as follows:1.In the wheat season,the soil microbial communities were significantly impacted by the N addition rate and growth stages.When the N addition rate exceeds 100 kg·hm^-2,the microbial diversity showed a downward trend.Microbial diversity had a positive correlation with average temperature during the wheat planting period.The soil microbial diversity and network complexity were at higher level under optimal N addition rate than other treatments.2.The asynchrony of soil microbial populations was improved by higher N addition rate in the wheat planting period.The asynchrony in Phenylobacterium and Desulfovirga were the potential factors to increase the wheat yield.N application could increase wheat yield by increasing the asynchrony of key microbial populations.3.In the rice planting period,the soil microbial communities were also significantly impacted by the N addition rate and growth stages.When the N addition rate exceeds 180kg·hm^-2,the microbial diversity showed a downward trend.The relationship of microbial diversity and precipitation was positive during the rice planting period.High N addition rate decreased the interactions within bacterial community.4.The asynchrony of soil microbial populations was improved by N addition rate in rice planting period.The asynchrony in Desulfovirga,Spartobacteria genera incertae sedis,Ohtaekwangia and Arenimonas were the potential factors to increase the rice yield.N application could increase the rice yield by increasing the asynchrony of key microbial populations,which probably facilitate the soil functional stability.5.When taking the rice-wheat seasons as a whole system,in which the soil microbial composition were different under different N addition rate,and the network of microbial communities was most complex at low N addition rate(140 kg·hm^-2).N addition rate enhanced the asynchrony of the microbial population to increase the yield of rice-wheat rotation.The asynchrony in Phenylobacterium,Gp I,Povalibacter,Pedobacter,Gp18,and Streptomyces were the potential factors to increase the yield of rice-wheat rotation,which could promote the yield of rice-wheat rotation system by enhancing the stability of microbial community functions.In summary,the effects of N addition on soil microbial communities existed at all growth stages in the rice-wheat rotation,while an optimal N addition rate can maintain higher soil microbial diversity and complexities of network.The asynchrony of soil microbial population increases the functional complementarity,and thus the increase of the asynchrony in key soil microbial populations is a potential mechanism for promoting the yield of rice-wheat rotation in N application condition.