Changes Of Contents And Chemical Composition Of Soil Labile Organic Carbon Fractions And Its Correlation With Soil Enzyme Activities Under Straw Incorporation Condition

Crop straw incorporation is a useful approach for increasing the quantity and changing the soil physical and chemical properties in agricultural ecosystem.However,few studies have focused on the effect of soil enzyme activities on carbon content and chemical structure of soil labile organic carbon(LOC)fractions with crop straw residues incorporation.The addition of crop residues not only increases soil N,P,K,but also generally results in greater organic carbon and enzyme activities in soil.We investigated the change of fertilization and residue incorporation on LOC fractions and straw-degrading enzyme activities in a 10-year continuous field experiment,and using solid-state nuclear magnetic resonance(NMR)spectroscopy,we investigated the effect of straw-degrading enzyme activities on chemical composition of soil organic matter(SOM),light fraction organic matter(LFOM),particulate organic matter(POM)and mineral organic matter(MinOM).The main results are as follows:(1)Straw incorporation can significantly increase the content of soil LOC fractions.Compared with the control treatment,after the straw was returned to the field,the content of light fraction organic carbon in the soil increased by 575%-725%,the content of easily oxidized organic carbon increased by 92%-115%,and the content of microbial biomass carbon increased by 22%-26%,soluble organic carbon content increased by 150%-217%.(2)Straw incorporation increased soil extracellular enzyme activity,increased cellulase activity by 4%-15%,increased ?-glucosidase activity by 40%-86%,and increased lignin peroxidase activity by 39%-68%,manganese peroxidase activity was increased by1%-48%,laccase activity was reduced by 68%-70%,and acid xylanase activity was not significantly changed.(3)Single application of chemical fertilizers and straw incorporation increased the relative content of alkoxy carbon in the SOM,LFOM and coarse particle organic matter(c-POM)fractions,and reduced the relative content of aromatic carbon.Compared with the control and single-fertilizer application,straw returning increased the relative content of alkyl carbon in the fine-grained organic matter(f-POM)and mineral-bound organic matter(MinOM).(4)Partial Least Squares(PLS)regression analysis of soil labile organic carbon and enzyme activities showed that cellulose,?-glucosidase and acidic xylanase play a positive and important role in the formation of light fraction organic carbon and permanganate oxidized carbon components.Also complied with the PLS regression equation,and thecorrelation coefficient range was 0.112-0.503.While for the formation of dissolved organic carbon and microbial biomass carbon components,soil hydrolases(cellulase,?-glucosidase and acid xylanase)all play a positive role and are higher than soil oxidases(lignin peroxidase,manganese peroxidase and laccase).(5)The correlation between carbon-containing functional groups of soil organic matter and soil enzyme activity showed that soil hydrolase has less effect on the chemical structure of soil organic matter,and has a greater influence on soil oxidase on the chemical structure of soil organic matter,especially for c-POM and MinOM components.