氮添加和固氮植物引种对喀斯特草地生态系统土壤有机碳矿化的影响OACHSSCD

Exogenous nitrogen(N)input was the key factor driving vegetation restoration and soil carbon(C)sequestration in Karst grassland ecosystems,which were undergoing N limitation.Soil organic carbon(SOC)mineralization was an important pathway for soil C output.However,most studies focused on the effects of N addition on SOC mineralization,while less attention was paid to the impacts of nitrogen-fixing plants.Thus,the effects of N input types,including N addition and introduction of nitrogen-fixing plants(Indigofera atropurpurea and Amorpha fruticosa),and N input amount(control,low N,and high N)on SOC mineralization and Q10 were investigated in a four-years experiment in a karst natural restoration grassland.The results showed that(1)Exogenous nitrogen input significantly increased soil ammonium nitrogen and available nitrogen contents,with maximum increases of 245.2%and 152.3%,respectively.Compared with low-density introduction of nitrogen-fixing plants,high-density introduction showed a decreasing trend in soil available phosphorus content.(2)N input amount significantly affected SOC mineralization,and low N input significantly increased SOC mineralization,especially in N addition and introduction of Indigofera atropurpurea,with increases of 14.4%and 21.5%,respectively.However,high N input trended to reduce SOC mineralization.N input reduced Q10,and the effect of low N input on reducing Q10 was more obvious than that of high N input.Especially for Indigofera atropurpurea,low-density planting significantly reduced by 19.0%compared to high-density planting.Redundancy analysis results showed that soil physicochemical properties explained 45.3%of the changes in SOC mineralization characteristics,with ammonium nitrogen and available phosphorus accounting for 15.4%and 18.8%,respectively.Soil available phosphorus was a major factor influencing SOC mineralization.This might be related to the phosphorus consumption during the biological N fixation by nitrogen-fixing plants.Soil N availability was a major factor influencing Q10,which might be related to the enhanced stability of SOC under increased N availability.(3)The form of N input had no significant effects on SOC mineralization and Q10.The effects of N addition and the introduction of Indigofera atropurpurea were similar,whereas Amorpha fruticosa showed a weaker impact.In summary,N input amount was more important for affecting SOC mineralization in the early stage of exogenous N input in Karst grassland ecosystems.Future increases in N deposition and the introduction of nitrogen-fixing plants were found to favor SOC retention in Karst grasslands.Additionally,Indigofera atropurpurea was identified as a preferred model for vegetation restoration in Karst grassland ecosystems.