Straw-returning reduces the contribution of microbial anabolism to salt-affected soil organic carbon accumulation over a salinity gradient

·In low-salinity soil,straw-returning did not change necromass contribution to SOC.·In medium-salinity soil,straw-returning reduced necromass contribution to SOC.·Straw-returning reduced POC contribution to SOC in lowsalinity soil.·Straw-returning increased POC contribution to SOC in medium-salinity soil.·Salinity affects the contribution of microbial-derived and plant-derived C to SOC.Salinization affects microbial-mediated soil organic carbon(SOC) dynamics.However,the mechanisms of SOC accumulation under agricultural management practices in saltaffected soils remain unclear.We investigated the relative contribution of microbial-derived and plant-derived C to SOC accumulation in coastal salt-affected soils under strawreturning,by determining microbial necromass biomarkers(amino sugars) and particulate organic C(POC).Results showed that,straw-returning increased necromass accumulation in low-salinity soil but did not change its contribution to SOC.In medium-salinity soil,straw-returning did not increase necromass accumulation but decreased its contribution to SOC.In low-and medium-salinity soils,the contribution of POC to SOC showed the opposite direction to that of the necromass.These results suggest that under straw-returning,the relative contribution of microbial-derived C to SOC decreased with increasing salinity,whereas the reverse was true for plant-derived C.Our results highlighted that straw-returning reduces the contribution of microbial anabolism to SOC accumulation in salt-affected soils with increasing salinity.