Effect Of Precipitation Change On The Stability Of Soil Aggregates In Desert Steppe

Soil aggregates maintain water,fertilizer,air and heat in the soil.The stability of soil aggregates reflects the carrying capacity,carbon fixation capacity and erosion resistance of soil,and represents the stability of soil.Precipitation,as the main limiting factor of plant growth in Inner Mongolia Desert Steppe,regulates the availability of C,N and P in soil aggregates.This study focused on the effects of different precipitation on the stability of soil aggregates in the Desert Steppe,the desert steppe of Stipa breviflora was selected as the research object in this study and relying on the simulated precipitation platform established in 2016,four plots with different precipitation gradients(50% water reduction,50% natural precipitation,50% water increase,100% water increase)were set up in each enclosed plot,soil samples from different soil layers(0～10 cm,10～20 cm,20～30 cm)were collected for aggregate screening from 2020 to 2021,the changes of nutrients and their stoichiometric characteristics in aggregates were measured.The main results and conclusions were as follows:(1)Reducing water by 50% significantly reduced litter biomass and soil water content(P<0.05),The underground biomass,soil water content and PH value of 0～10cm were increased by 100% water increase(P<0.05).The soil bulk density of 0～10 cm was significantly decreased by 100% water increase treatment(P<0.05).In the wet year,the content of organic carbon in 0～10cm under 100% water increase was significantly higher than that under 50% water reduction(P<0.05),The total nitrogen content of 10～20 cm under100% water increase was significantly higher than that under 50% water increase(P<0.05),The total phosphorus content in 0～10cm soil layer was decreased by 50% water reduction(P<0.05).In the dry year,the content of soil organic carbon decreased with the increase of precipitation gradient,The total nitrogen of 100% water increase was significantly lower than that of 50% water reduction(P<0.05).(2)In the wet year,soil mechanical stability aggregates were dominated by large aggregates(>0.25 mm),accounting for 50.1%～65.4% of the total aggregate content,soil water stability aggregates were accounting for 31.4%～44.6% in 0～30cm layers.In the dry year,soil mechanical stability aggregates were accounting for 40.1%～62.4%,soil water stability aggregates were accounting for 28.4%～44.3%.Some mechanical stability aggregates with particle size >0.25 mm collapse into 0.053～0.25 mm aggregates under hydraulic action.The increase of water content significantly increased the content of large soil water-stable aggregates(P<0.05),and as the precipitation gradient increased,the stability of water-stable aggregates in 0～10 cm soil layer increased significantly in 2020.With the increase of soil depth,the soil erodibility factor K of 2021 increased significantly,and the stability of soil aggregates decreased significantly(P<0.05).(3)The organic carbon,total nitrogen and total phosphorus in the water-stable aggregates were mainly concentrated in the larger aggregates of >0.25 mm particle size.In the wet year,50% water reduction significantly decreased the content of organic carbon in10～20 cm soil(P<0.05).In the dry year,50% water increase significantly reduced the content of organic carbon in the particle size of <0.053 mm in 0～10 cm soil layer(P<0.05).50% water reduction wasn’t conducive to the accumulation of total nitrogen and total phosphorus in 0.25～2 mm particle size in 0～20 cm soil layer,and 100% water increase significantly increased the contents of total nitrogen in 0.25～2 mm particle size and total phosphorus in >2 mm particle size in 0～10 cm soil layer(P<0.05).The C/N of aggregates in0～10 cm soil layer was significantly higher than that in the other two soil layers(P<0.05).Increasing water by 100% significantly increased the N/P of aggregate(P<0.05).The contribution rate of organic carbon,total nitrogen and total phosphorus to total organic carbon,total nitrogen and total phosphorus in the aggregate of 0～20 cm soil layer is the highest with the particle size of 0.053～0.25 mm.(4)The contents of microbial biomass carbon and nitrogen were higher in 0～10 cm soil layer,and the microbial biomass carbon in 0～10 cm soil layer was mainly concentrated in0.25～2 mm particle size aggregate,which had a significant univariate linear relationship with SOC in the aggregate(P<0.01).(5)In wet years,the limiting effect of water on the ecosystem was weakened.It had a significant impact on soil erodibility factors by affecting soil bulk density,pH,microbial biomass carbon,under-ground biomass and organic carbon content;In dry years,soil water content directly had a very significant negative effect on soil erodibility factors(P<0.001).In summary,increasing water was beneficial to the accumulation of soil mass(>0.25mm)in all soil layers(0～30 cm),the soil erosion resistance was improved,the soil stability was enhanced,the soil nutrient was stored,and the desert grassland was long-term sustainable utilization.