Effect On Nitrogen And Carbon Content And Microbial Community Structure Of Wheatsoybean Rotation Soil Under Straw Return And Fertilizer Application Treatments

Straw retention and optimized fertilization,which maintain soil fertility,enhance the ability of soil carbon sequestration in farmlands,are important strategies for enabling high-quality sustainable development in agriculture.Currently,the most important scientific issues concerning agriculture and the environment are the effects of straw retention and optimized fertilizer application on the mechanisms of soil nitrogen and carbon fractionations,as well as the dominant factors and responses of the soil bacterial community.This experiment was conducted for over 10 years on an experimental field in the Northwest A&F University campus,using a randomization design.Nine combination treatments with three fertilizer and three straw retention levels were designed.The three straw retention treatments included the following:?1?complete straw retention?TS?;?2?50%straw retention?HS?;?3?no straw retention?NS?.The three fertilizer application treatments included the following:?1?the local farmers'traditional practice rate?TF?;?2?optimized fertilization?0.8TF?,corresponding to 80%of the TF fertilizer rate;?3?no fertilizer application?NF?.Using a high-throughput Illumina Hi Seq sequencing platform and redundancy analysis?RDA?,we aimed to identify the following:?1?the dynamic changes in different fractions of soil carbon and fractions of soil nitrogen;?2?the structure and diversity of the soil microbial community and the relationship between the soil microbial community and soil quality effects based on straw retention and fertilizer treatments.The results showed the following:1.Effects on the dynamic changes of the soil nitrogen contents and fractions in response to straw retention and fertilizer treatmentsThe straw retention and fertilizer application treatments marked enhanced the soil TN,NH₄⁺-N,and NO₃^--N contents,with significant differences between the different treatments.The ranges of the soil TN and NH₄⁺-N were not significantly different among the treatments during the different seasons.However,the soil NO₃^--N was significantly different among the treatments during the growth periods of winter wheat and summer soybean.The soil NO₃^--N content during autumn and winter was higher than that during spring,from March to May?the wheat growth period?.The soil NH₄⁺-N and NO₃-N contents increased upon increasing the amount of nitrogen applied.However,the soil MBN content decreased upon increasing the amount of nitrogen applied.The MBN content increased in response to the 0.8TF treatment compared to that in response to the NF treatment,but decreased in response to the TF treatment.During the early period of straw decomposition,the soil NH₄⁺-N content in the TS treatment was lower than that in the HS treatment.The NO₃-N and MBN contents increased upon increasing the straw retention.Significant differences in the MBN and NO₃-N contents were observed between different straw retention treatments,and the MBN and NO₃-N contents were higher in the surface soil than in the subsoil.The mean soil TN and MBN contents in the 0.8TF+TS treatment group were higher than those in the other treatment groups?1.06 g/kg and 36.59 mg/kg,respectively?.The mean soil NH₄⁺-N and NO₃-N contents were optimal under conditions of TS+TF treatment?2.37 and15.93 mg/kg,respectively?.2.Effects on the dynamic changes in the soil carbon contents and fractions in response to straw retention and fertilizer application treatmentsLong-term straw retention and fertilizer application treatments improved the contents of SOC,SDTC,SDOC,and SIC,but showed no significant effects on the SOC content.However,the compositions of the different carbon fractions in the soil changed remarkably.The SDOC/SDTC rate increased upon increasing the amount of nitrogen applied.The SDIC/SDTC rate decreased first and then increased upon increasing the amount of nitrogen applied,while the soil MBC content first increased and then decreased.The MBC content increased upon increasing the amount of straw retention,while the SDTC/SOC and SDIC/SOC rates decreased.The MBC/SOC rate increased first and then decreased upon increasing the amount of straw retention.The soil C/N ratio decreased upon increasing the amount of nitrogen applied,but increased upon increasing the amount of straw retention.The MBC/MBN rate increased upon increasing the amount of nitrogen applied,but decreased upon increasing the amount of straw retention.The SOC,SDOC,and MBC contents were the highest in the TF+TS treatment group?12.14 g/kg,95.70 mg/kg,and 345.53 mg/kg,respectively?.The mean soil SDTC content was198.90 mg/kg in the 0.8TF+TS treatment group,which was higher than that in the other treatment groups.Average soil SDIC was 119.73 mg/kg in the TF+NS treatment group,which was higher than that in the other treatment groups.3.Responses of the microbial community and diversity to straw retention and fertilizer applicationWith respect to bacterial diversity in the soil,the chao1,ACE,and Shannon indexes first increased and then decreased upon increasing the amounts of straw retention and nitrogen applied.The Simpson index increased upon increasing the amount of nitrogen applied,and decreased upon increasing the amount of straw retention.The number of OTUs in December was higher than that in June after the wheat harvest.Under all treatment conditions,the dominant bacterial phyla in the soil were Proteobacteria?28.06%?,followed by Acidobacteria?24.05%?,Gemmatimonadetes?13.09%?,and Actinobacteria?10.68%?.With respect to the soil fungal diversity,the chao1,ACE,and Shannon indexes decreased upon increasing the amount of nitrogen applied.The chao1 and ACE indexes increased upon increasing the amount of straw retention,while the Simpson and Shannon indexes decreased.Under all treatment conditions,the dominant fungal phyla was Ascomycota,which relative abundance accounted for 53.53%.Ascomycota,Basidiomycota,Chytridiomycota,and Zygomycota in the 0.8TF and TF treatment groups were-2.42%and 2.30%,-5.35%and-9.52%,-1.99%and 22.04%,and 21.57%and 71.73%,respectively compared to their levels in the no fertilizer treatment group.Further,Ascomycota,Basidiomycota,Chytridiomycota,and Zygomycota in the HS and CS treatment groups were-7.53%and-6.37%,14.77%and 3.41%,-4.57%and-11.85%,and-38.79%and 49.12%,respectively compared with their levels the NS group.4.Relationship between the microbial community and soil carbon and nitrogen in response to the straw retention and nitrogen application treatmentsThe soil moisture content and p H decreased after the long-term application of fertilizer,but increased after straw retention,and the yield of wheat and soybean had increased by the straw retention and fertilizer application.RDA analysis revealed a correlation between the chao1,Simpson,ACE,and Shannon indexes,which were positively correlated with the soil IC content negatively correlated with the following:water moisture;TN,NH₄⁺-N,NO₃-N,IN,and SDOC content;SDOC/SOC rate;p H.Proteobacteria was positively correlated with the SDIC and MBC content,and IC/TC rate,and negatively correlated with the SOC content.The chao1 and ACE indexes of the soil fungal diversity were negatively correlated with the MBN content and NH₄⁺-N/TN rate,and positively correlated with SDIC content.The Simpson and Shannon indexes were positively correlated.At the phylum level,Ascomycota was negatively correlated with the SOC and MBC contents.Basidiomycota was negatively associated with Chytridiomycota and the SDIC content.Zygomycota was positively correlated with the IC/SOC.It was concluded that the long-term applications of straw retention and fertilizer can markedly improve the nitrogen and carbon contents in the soil under wheat-soybean rotation.The mean soil TN,MBN and DOC contents in the 0.8TF+TS treatment group were higher than those in the other treatment groups,the mean yield of boybean and wheat had redcrease about 0.55%,but saving 20%fertilizer,it is a mode for enabling high-quality sustainable development in agriculture.The soil p H is one of dominant factors affecting the composition of bacterial communities.We found that high levels of N addition significantly decreased the soil bacterial diversity and altered the composition of the soil bacterial community.Dynamics change of microbial community and the relative abundance at Phylum of soil fungi and bacterial under different strawretention and fertilizer application is the paper's innovation point...