Effects Of No-tillage And Straw Return On Soil Organic Carbon Pool And Microbial Diversity In Rice–wheat Systems

Soil organic C?SOC?has a profound impact on soil health and productivity.No-tillage and straw return practices are considered as efficient ways to increase SOC content.Although many studies reported the effects of different tillage practices and straw return methods on crop yield,SOC pool and soil microbial diversity.However,little attention was paid to the relationship between SOC pool and soil microbial community.However,the mechanisms how soil microbial community affect SOC content under no-tillage and straw return remain unclear.Therefore,it is worthy to evaluate the effects of no-tillage and straw return on SOC fractions,greenhouse gas emissions and soil microbial diversity,and reveal the relationships between soil microbial community and SOC pool.This field experiment was conducted in Dafashi downtown,Wuxue City,Hubei province,during2012-2014.The rice-wheat system,which is one of main cropping systems in the middle reaches plain of the Yangtze River,was selected in this study.The field experiment follows split block design,and tillage practices[no-tillage?NT?and conventional intensive tillage?CT?]as main plots and straw return methods[crop straw removal?NS?and straw return?S?]as subplots with three replications,a total of 12 plots.The experimental treatments include conventional intensive tillage with straw removal?CTNS?,conventional intensive tillage with straw returning?CTS?,no–tillage with straw removal?NTNS?and no–tillage with straw returning?NTS?.After 3 cycles of rice-wheat system,the experimental results as follows:?1?Tillage practices and straw return methods significantly affected soil dissolved organic carbon?DOC?and soil organic carbon?SOC?,soil microbial biomass carbon?MBC?contents and soil aggregate SOC in 0⁵ cm soil layer.Compared with CT,NT increased DOC,MBC,SOC,2¹ mm and 1⁰.25 mm aggregate SOC contents by8.6%¹2.3%,15.1%³9.8%,2.3%¹5.5%,4.6%¹9.9%and 13.4%¹4.6%,respectively.Relative to NS,straw return increased DOC,MBC and SOC,2¹ mm and 1⁰.25 mm aggregate SOC contents by 13.0%²3.8%,18.1%²7.8%,6.5%⁹.1%,12.5%¹7.4%and 6.2%⁷.0%,respectively.?2?Tillage practices and straw return methods significantly affected soil CO₂ and CH₄ emissions,while having no significant effect on N₂O emission.In comparison to CT,NT reduced CO₂ and CH₄ emissions by 7.2%¹9.8%and 5.8%¹9.7%,respectively.Compared with NS,straw return increased CO₂ and CH₄ emission by 9.1%⁴.1%and18.6%²32.9%,respectively.?3?Tillage practices and straw return methods significantly influenced soil microbial community structure and bacterial diversity,indicated by Simpson index and Shannon-weaver index.NT increased soil bacterial biomass,Simpson index and Shannon-weaver index by 45.4%⁷4.6%,2.3%³.4%and 6.1%¹2.2%,relative to CT,while NT decreased Gram-positive bacteria/Gram-negative bacteria?G⁺/G^-?and monounsaturated fatty acids/saturated fatty acids?MUFA/STFA?by 12.0%²5.4%and28.2%⁴2.3%,respectively,relative to CT.Compared with NS,straw return increased soil bacterial biomass,MUFA/STFA,Simpson index and Shannon-weaver by20.6%⁵8.1%,5.9%³0.0%,3.1%and 12.8%,respectively,while straw return reduced G⁺/G^-by 9.5%²0.7%.?4?Tillage practices and straw return methods significantly affected soil microbial functional diversity indicated by Shannon-weaver index,Simpson index and Pielou index.Compared with CT,NT enhanced Shannon-weaver index,Simpson index and Pielou index by 1.9%⁷.1%,0.3%¹.3%and 1.3%².7%,respectively.Straw return increased Shannon-weaver index,Simpson index and Pielou index by 1.1%⁸.8%,0.2%¹.5%and1.3%³.8%,respectively.?5?In conclusion,no-tillage and straw return increased SOC content in 0⁵ cm soil layer.Soil bacteria may mediate SOC by affecting the macro-aggregate SOC and CH₄emission under different tillage practices and straw return methods under rice-wheat systems.No-tillage and straw return are effective options to increase the SOC content in lowlands in the middle reaches of the Yangtze River.Nonetheless,further research is needed to explore the relationship between soil microbial community and SOC fractions in 0²0 cm soil layer.