Effects Of Straw Amendment On Arbuscular Mycorrhizal Fungi And Its Relationship With Nitrous Oxide Emissions In The Wheat Field After Rice Cultivation

Nitrous oxide(N2O)is one of the main greenhouse gases,and agriculture is the most important source of nitrous oxide emissions.Straw returning to the field is one of the commouly used farmland management measures in the process of agricultural production.However,the mechanism of nitrous oxide emission under straw returning condition is not clear at present.Arbuscular mycorrhizal fungi(AMF)are widely distributed in farmland ecosystem and play an important role in soil nitrogen cycling.Based on a long-term straw return experiment,this studyaimed at the rice-wheat rotation system in the middle and lower reaches of the Yangtze river agricultural distirct,set up three straw return methods:straw removal with minimum tillage(CK)3 rotary tillage straw return(RT-SR)and ditch-buried straw return(DB-SR)and investigated the following questions:,1)how different straw return methods impact AMF community;2)How AM F influnce soil nutrient availability,nutrient uptake and yield of wheat under different straw return methods;3)How AMF affect soil denitrification and N2O emission under different straw return methods.This study tried to explore the mechanisms of N2O emissions under straw return based on the hypothesis of mycorrhiza-mediated N uptake by plantsfarmland under the condition of driving mechanism of,and the results will provide theoretical evidence for reducing N2O emissions in farmlands,and thus enrich soil microbial ecological functioning in agroecosystems.1.Responses of AMF community to different straw return modes in the wheat fieldsSignificant difference was found in AMF community composition among different straw returning methods.In the 0-10cm soil layer,compared with CK,RT-SR and DB-SR significantly decreased Shannon-Weiner diversity index.Compared with CK and DB-SR,RT-SR significantly increased Shannon-Weiner diversity index and Margalef index in 10-20cm soil layers,while species eveness was significantly decreased in bothsoil layers.Compared with CK,AMN root colonization rate was also significantly decreased under RT-SR and DB-SR,respectively.In 0-10cm soil layer,EEG content of RT-SR and CK was significantly higher than DB-SR,while EEG content of DB-SR was significantly higher than CK in 10-20 cm soil layers.There was no significant difference for TG content among different straw return methods.In addition,benomyl treatment can significantly change AMF community composition and reduce AMF activity.2.Effects of AMF on soil organic carbon and nutrient under different straw return methodsThe effects of AMF on soil organic carbon and nufflients depend on different straw return methods and wheat growth stage.AMF significantly impact soil organic carbon content in 10-20 cm soil layer in the whole growth stages of wheat plants.However,AMF significantly reduced soil organic carbon content in 0-10 cm soil layer in the grain-filling stage under three straw return methods,and decrecreased soil organic carbon content under RT-SR at booting stage,while no difference was found for other times.AMF sig1ificantly influence total nitrogen content in 0-10cm and 10-20cm soil layers under CK,but exerted a greater effect in 0-10cm than 10-20cm soil layers under RT-SR and DB-SR in comparison with CK for each growth stage.NH4+-and NO3--N content showed large variations in different growth stages.The maximum of NH4+-N content was shown in the grouting period,while NO3--N content reached the highest in the rising and heading period.AMF has a significant influence on soil available phosphorus content under different straw return methods(P<0.05).In 0-1 Ocm soil layer,AMF significantly reduced soil available phosphorus in most of growth stages under different straw return methods.However,AMF significantly increased available phosphorus under CK and DB-SR but decreased for RT-SR in 10-20 cm soil layer for most of the growth periods.3.Effects of AMF on denitrifying enzyme activity and N20 emission under straw amendmentAMF significantly affected soil denitrifying enzymatic activity and N2O emission under straw amendment,but its effect depended on straw return method and wheat growth stage.AMF had no obvious effect on denitrifying enzyme activity at erection stage under RT-SR,but significantly increased denitrifying enzyme activity in other growth period under RT-SR.Under DB-SR treatment,AMF significantly increased denitrifying enzyme activity in the erection stage,but reduced or showed no effect on denitrifying enzyme activity in other growth strages.Under CK treatment,AMF significantly decreased denitrifying enzyme activity at tillering and heading stage,while significantly increased denitrifying enzyme activity at other growth stages.According to the accumulative data of the whole growth period,AMF promoted N2O emission under CK,while promoted N2O abso:r:ption under RT-SR and DB-SR.