Effects Of Manipulated Precipitation On Soil Organic Carbon And Its Stability In Desert Steppe Of Western Loess Plateau

Precipitation pattern change is one of the main manifestations of global change.How precipitation change affects the stability of soil carbon pool is a key link in the study of terrestrial ecosystem carbon cycle.Soil organic carbon and its components are important indexes reflecting the dynamic changes of soil organic carbon pool and have a very important influence on the stability of soil organic carbon pool.The desert steppe in the west of loess Plateau is located in semi-arid region,where precipitation is scarce and vegetation is sparse.The ecosystem is very fragile,which plays an important role in maintaining the stability of regional ecosystem.However,the effect and mechanism of precipitation change on the stability of carbon pools in this region are not clear.Therefore,the study on the impact of precipitation change on soil organic carbon components and its stability in this region is of great significance to accurately assess the response of soil carbon sink potential to global change,and is also a positive response to the national policy of "carbon peak and carbon neutralization".In this study,five precipitation gradients(40% reduction,20% reduction,control,20% increase and 40% increase)were set up in a field controlled precipitation experiment on the western desert steppe of the Loess Plateau.Analysis methods such as variance analysis,correlation analysis and structural equation model were used to reveal the change rules of enzyme activities,organic carbon components and stability of organic carbon in desert steppe under precipitation change,and further explore the mechanism of influencing stability of organic carbon.The main results are as follows:(1)Precipitation treatment had significant effects on catalase,sucrase,urease and GME activity in 0-5cm soil layer,and the GME activity in 0-10 cm soil layer and5-10 cm soil layer were significantly lowest under +20% treatment,and catalase activity under-20% treatment was significantly lower than that under-40% treatment.In addition,the geometric mean values of urease,sucrase,neutral phosphatase and soil enzyme activities under precipitation treatment decreased with the increase of soil depth.In conclusion,precipitation treatment had a significant effect on the enzyme activity in 0-10 cm soil layer,and the enzyme activity decreased with the increase of soil depth under precipitation treatment.(2)Precipitation treatment had no significant effects on soil organic carbon(SOC),microbial biomass carbon(MBC),dissolved organic carbon(DOC)and geometric mean value of labile organic carbon(GMC),but had significant effects on light organic carbon(LFOC)and recombinant organic carbon(HFOC).LFOC in0-5cm soil layer under-40% treatment was significantly lower than that under control(LFOC in other soil layers also showed the same trend),and recombinant organic carbon under +40% treatment was significantly higher than that under control and+20% treatment,indicating that extreme water reduction significantly reduced active organic carbon in 0-5cm soil layer.Extreme water increase enhanced the conversion of inert organic carbon in soil by increasing organic matter input and microbial enzyme reaction.Meanwhile,SOC,MBC,LFOC and GMC all decreased with increasing soil depth,while DOC increased with increasing soil depth under +20%treatment.Precipitation treatment had no significant effect on soil depth.(3)Precipitation treatment only had a significant effect on LFOC/SOC in 0-5cm soil layer,and LFOC/SOC in-40% soil layer was lower than that in the control layer,indicating that extreme water reduction slowed down the conversion rate of SOC to light organic carbon in 0-5cm soil layer.Meanwhile,the LFOC/SOC of 0-10 cm soil layer is usually higher than that of 10-20 cm soil layer.Under precipitation treatment,the microbial entropy(MBC/SOC)decreased with the increase of soil depth,indicating that the efficiency of converting SOC to MBC decreased with the increase of soil depth.DOC/SOC increased with the increase of soil depth under-40% and+20% treatments,while it was lowest in 5-10 cm soil layer under other precipitation treatments.(4)Altered precipitation would affect soil sucrase,catalase activities and soil labile organic carbon components by affecting available phosphorus,conductivity,plant coverage and litter quantity,and then ultimately affect the stability of organic carbon.In conclusion,soil available nutrients,plant characteristics and soil enzyme activities are the main factors affecting soil organic carbon stability under precipitation change.