Effects Of Vegetation Degradation On Soil Physicochemical Properties And Enzyme Activities Of Gahai Wet Meadow

The degradation of wetland vegetation caused by climate change and human activities is a hot issue worldwide.This degradation phenomenon will affect soil physicochemical properties and enzyme activities due to changes in environmental conditions.However,little is known about the changes of soil physicochemical properties and enzyme activities of high altitude wet meadows under different vegetation degradation levels.Therefore,to study the changes of soil physicochemical properties(p H;porosity;particle composition;bulk density,BD;total nitrogen,TN;total phosphorus,TP;soil organic carbon,SOC;microbial biomass carbon,MBC;dissolved organic carbon,DOC;easily oxidized organic carbon,EOC;particulate organic carbon,POC;light fraction organic carbon,LFOC)and enzyme activities(urease,amylase,catalase and sucrase)and their relationship in the process of vegetation degradation(four vegetation degradation levels:primary wet meadow,ND;lightly degraded,LD;moderately degraded,MD;and heavily degraded,HD)in the Gahai wet meadow is particularly important for regulating the stability of soil organic carbon components and improving the carbon sink function of the degraded wet meadow ecosystem at high altitude.Based on the mechanism trend analysis of a large number of experimental data indicators,the linear regression analysis in the SPSS19.0 and the Pearson analysis method are used to analyze the correlation between different indicators,and the following conclusions are drawn:1.With the intensification of vegetation degradation,the value of BD increased,and the reduced soil aeration is not conducive to the extension and growth of plant roots.The average soil bulk density increased from 0.46 g·cm^-3in the ND plot to 0.71g·cm^-3in the HD plot;the p H values of the soil were all weakly alkaline;the soil particle composition changed from fine sand(<0.2 mm)(54.52%)to coarse sand(2?0.2 mm)(57.02%).In addition,the cycling and transformation ability of soil nutrients has gradually decreased with the intensification of vegetation degradation,resulting in the deterioration of soil environment in wet meadow.The contents of soil SOC and TN decreased significantly,while soil TP increased gradually(the soil TP content in HD was the highest,was 50.91 mg·kg^-1);soil C:N was lower than chinese average soil C:N(14.4),and soil C:P and N:P were significantly higher than that of chinese soil(136 and 9.3).2.With the intensification of vegetation degradation,the contents of soil carbon showed a decrease trend.The contents of SOC,MBC,DOC,EOC,POC and LFOC in the 0-100 cm layer of ND soil were 50.77%,30.46%,49.89%,45.09%,114.65%and186.84%higher than those of HD,respectively.With the increase of soil depth,the content of different soil SOC components decreased,and all had obvious surface aggregation phenomenon(0-20 cm layer).In addition,the monthly and seasonal dynamics of different soil SOC components was not consistent.In addition,soil SOC and POC,EOC,MBC,DOC,and LFOC showed a very significant positive linear relationship(P<0.01),and R²reached 0.9153,0.946,0.8957,0.8991 and 0.8305,respectively.The different soil SOC components had a very significant negative correlation with soil BD,a significant positive correlation with p H and TN(P<0.01or P<0.05),and a weak positive or negative correlation with soil TP(P>0.05).3.With the intensification of vegetation degradation,the soil enzyme activities decreased gradually.The ND soil amylase,catalase and sucrase activities in the 0-100cm layer were 30.53 mg·g^-1,0.20 ml·g^-1and 71.56 mg·g^-1higher than those of the HD soil,while the urease activities in HD soil were the highest(137.17 mg·g^-1).Season and vegetation degradation had significant interaction on the four enzyme activities,and the seasonal variation of different enzyme activities was not consistent.In addition,the soil BD and p H value had significant negative correlation with four enzymes(urease,catalase,amylase,sucrase)(P<0.01 or P<0.05);there was a significant positive correlation between TN and catalase,amylase and sucrase in soil,but negatively correlated with urease(P<0.01);there was a significant positive correlation between soil TP and sucrase enzyme(P<0.01),and a weak negative correlation with catalase and amylase(P>0.05).The four soil enzyme activities and SOC showed a very significant positive linear relationship(P<0.01).4.With the intensification of vegetation degradation,soil active carbon,carbon pool management index and comprehensive score of soil quality decreased significantly,vegetation degradation had a significant impact on soil quality and carbon pool characteristics of wet meadow.The soil active carbon content of the ND plot in the 0-100 cm layer was 0.59 g·kg^-1,0.76 g·kg^-1and 0.90 g·kg^-1higher than that of LD,MD and HD,respectively.The soil carbon pool management index of the ND plot in the 0-100 cm layer was 20.36%,25.96%and 30.56%higher than that of LD,MD and HD,respectively.The comprehensive score of soil quality was ND>LD>MD>HD.The results showed that heavily vegetation degradation could significantly reduce the content of soil organic carbon components and the rate of enzymatic reaction at 1 m depth.If the wet meadow continues to degradation in the future,the process of wetland vegetation restoration will be very difficult,resulting in a serious reduction of soil productivity and SOC storage,eventually,the function of wet meadow ecosystem will be completely transformed from“carbon sink”to“carbon source”.The research results provide technical parameters for scientific understanding and evaluation of soil carbon changes under the condition of vegetation degradation in wet meadow of QTP in China,and provide a theoretical basis for alpine wet meadow ecosystem to regulate the stability of soil organic carbon components and improve its carbon sink function.