翻耕和植物残体覆盖对"黑土滩"型退化草地土壤氧化亚氮排放的影响OA北大核心CSTPCD

Grassland restoration is the key measure to promote the restoration of the grassland ecosystem and achieve sustainable development.The aim of this work was to explore the effects of plowing and mulching with plant residues on soil nitrous oxide(N2O)emissions from an extremely degraded alpine grassland.The experiment was conducted in an alpine meadow in Hongyuan County,Sichuan,China,on the Eastern edge of the Qinghai-Tibetan Plateau.The experiment consisted of a control(CK)and three treatments;i.e.,black soil beach-type degraded grassland with roots removed from the 0-20 cm soil layer and no plant residues(CK),plowed degraded grassland(PL),degraded grassland mulched with plant residues(MR),and plowed degraded grassland mulched with plant residues(PL+MR).We measured soil basic physical and chemical indicators,microbial biomass,extracellular enzyme activity,nitrification enzyme activity,denitrification enzyme activity,functional microbial gene abundance,and 28-day cumulative N2O emissions.The results showed that,compared with CK,PL significantly increased cumulative soil N2O emissions(by 44.2%).Soil N2O emissions were significantly lower in PL+MR(by 29.1%)than in PL.Compared with CK,PL significantly enhanced soil pH(by 2.6%),increased dissolved organic carbon(DOC)and microbial biomass carbon(MBC)concentrations(by 209.5%and 23.8%,respectively),increased activities of β-1,4-glucosidase(BG)and β-1,4-N-acetylglucosaminidase(NAG)(by 180.4%and 233.9%,respectively),and increased abundance of amoA genes of ammonia-oxidizing archaea(AOA)and ammonia-oxidizing bacteria(AOB)(by 74.6%and 68.0%,respectively).Compared with CK,PL significantly decreased soil C/N(by 11.3%),decreased soil organic carbon(SOC)and microbial biomass nitrogen(MBN)concentrations(by 13.6%and 72.8%,respectively).Compared with PL,PL+MR significantly decreased soil DOC concentration(by 12.8%),significantly reduced BG,NAG,leucine aminopeptidase(LAP)and acid phosphatase(AP)activities(by 49.1%,59.9%,31.6%,and 25.0%,respectively),and decreased AOA-amoA,AOB-amoA,and nosZ I genes abundance(by 46.5%,59.5%,and 23.1%,respectively).Compared with PL,PL+MR significantly increased MBN concentration(by 29.1%).Correlation analyses showed that cumulative soil N2O emissions were significantly positively correlated with the pH,DOC concentration,extracellular enzyme activity,and abundance of genes related to the nitrogen cycling(except nirS),and significantly negatively correlated with C/N,SOC and MBN concentrations.The abundance of AOA-amoA and AOB-amoA were the key factors affecting N2O emissions.In summary,plowing resulted in enhanced soil extracellular enzyme activity and amoA gene abundance,as well as increased SOC decomposition and consumption and N2O emissions.Mulching with plant residues effectively alleviated these negative effects,indicating that it is a feasible improvement measure.