Effects Of Short-term Nitrogen And Phosphorus Addition On Soil Labile Organic Carbon And Its Components In Desert Grassland

Nitrogen(N)and phosphorus(P)are major limiting factors for plant growth in terrestrial ecosystems.The ecological environment of the desert grassland in Ningxia is fragile and the mineralization is weak,so the plant growth is further restricted by nutrients.The effects of N and P addition on the accumulation and stability of soil organic carbon are altered by changing the input of organic matter and the chemical composition of the soil.To determine how the effects of N and P addition on soil labile organic carbon components and carbon pool stability,we conducted a field fertilization experiment with N and P addition in desert grassland.The content and efficiency of particulate organic carbon(POC),light fraction organic carbon(LFOC),easily oxidized organic carbon(EOC),dissolved organic carbon(DOC),and microbial biomass carbon(MBC),and sensitivity index(SI)and carbon management indicator(CMI)were analyzed.The results showed that:(1)Soil organic carbon(SOC)and soil POC content in topsoil(0-10 cm layer)significantly increased with nutrient addition(N addition,P addition,and N and P addition together).And soil LFOC content in 0-30cm layer significantly increased with nutrient addition.SOC content in 20-30 cm layer significantly decreased with P addition.Soil POC proportion in 0-20cm layer significantly increased with nutrient addition(N addition,P addition,and N and P addition together).Soil LFOC proportion in 0-30cm layer increased significantly with N addition,and soil LFOC proportion in 10-30cm layer significantly increased with P addition,N and P addition together.Nutrient addition increased the unprotected soil organic carbon proportion,and decreased conversion rate of unprotected soil organic carbon to protected soil organic carbon.Therefore,nutrient addition was detrimental to the stability of soil organic carbon in desert grassland.(2)Soil EOC and DOC content in topsoil significantly increased with N and P addition together.But soil MBC content in topsoil significantly decreased with N and P addition together.Soil EOC proportion in 10-20cm layer significantly increased with N addition or P addition.Soil DOC content and proportion in 10-20cm layer significantly increased with N addition or P addition,but soil MBC content in 20-30cm layer significantly decreased.(3)The sensitive index of EOC,DOC,and LFOC were highly sensitive to nutrient addition,and could be used as the indicator for the effect of SOC with short-term N and P addition in desert grassland.The CMI values calculated by EOC gradually declined with increasing soil layer of desert grassland.The CMI values calculated by EOC,DOC,and LFOC increased with nutrient addition,which indicated that short-term N and P addition has the potential to improve soil quality and fertility,and to promote soil restoration in desert grassland.There was a positive correlation between POC,LFOC,EOC,DOC,MBC,and SOC.The principal components analysis(PCA)of six soil variables was used to represent the correlations among the variables of the first two principal axes associated with the first two principal components.PCA axis 1 primarily reflected SOC and the physical fractionation of labile soil organic carbon and accounted for 93.2%of the overall variance in the standardized soil variables,which indicated that the effects of short-term N and P addition on soil carbon pool and soil stability in desert grassland could be better reflected by SOC and the physical fractionation of soil labile organic carbon.