Changes In Soil Physicochemical And Biological Properties Of Grassland In Different Years Of Enclosure On The Loess Plateau

As a valuable natural resource of the Loess Plateau,grassland is affected by extreme weather and grazing activities,and grassland degradation is intensified.The implementation of enclosure measures in degraded grassland is conducive to the natural restoration of grassland.In this study,we studied the physicochemical and biological properties of the surface soil in the enclosed grassland with different recovery years?10,25,35 years?and grazing grassland on the Loess Plateau,and explored the changes law and correlation of various properties of the soil in recovery,provided the guiding role for the restoration and management of the degraded grassland on the Loess Plateau.The results showed that:?1?Long-term enclosure significantly changed the physical and chemical properties of the soil.With the prolongation of enclosure years,the soil bulk density gradually decreased,the soil moisture gradually increased,the pH increased first and then decreased,and the nitrate nitrogen and available phosphorus content decreased first and then increased,the effect of enclosure on ammonium nitrogen is not significant.Enclosure significantly affected soil C,N,and P content,organic C and total N increased,while total P decreased.Enclosure also significantly increased soil C:P,N:P,but had no significant effect on C:N.?2?Soil organic carbon was positively correlated with soil moisture and total nitrogen,but negatively correlated with soil bulk density.There was a significant negative correlation between total nitrogen and nitrate nitrogen.Total phosphorus was negatively correlated with soil moisture,but positively correlated with soil bulk density.There is a very significant negative correlation between soil bulk density and soil moisture.Soil C:P was positively correlated with N:P and soil moisture,positively correlated with total nitrogen and negatively correlated with soil bulk density.Soil N:P was positively correlated with organic carbon,but negatively correlated with nitrate nitrogen.?3?Microbial biomass C and N increased significantly with the increase of enclosure time,and decreased or remained stable for 35 years.Microbial biomass C:N decreased gradually with the development of enclosure.Microbial biomass C:N had no significant relationship with soil C:N.Long-term fencing significantly affected the change of C:N imbalance,which was higher in the later stage of fencing.However,enclosure had no significant effect on soil microbial quotient qMBC and qMBN.?4?There was a very significant positive correlation between microbial biomass carbon and microbial biomass nitrogen,and both of them had a very significant positive correlation with total nitrogen content.Microbial biomass nitrogen was positively correlated with soil moisture and organic carbon,but negatively correlated with total phosphorus.Microbial biomass C:N was positively correlated with soil bulk density and total phosphorus,but negatively correlated with soil moisture,ammonium nitrogen and organic carbon.?5?The activities of BG,NAG and AKP increased significantly with the prolongation of the enclosure time,and then decreased significantly.The activity of BG and NAG reached the highest in 25 years of enclosure,244.57 nmol·g^-1·h^-1and 36.48 nmol·g^-1·h^-1,respectively.The peak of AKP activity appeared in the enclosure for 10 years(498.04nmol·g^-1·h^-1).Long-term enclosure had a significant effect on the stoichiometry of the three enzymes.The changes of BG:NAG in the early and middle stages of recovery were relatively stable,and reached the highest level in 35 years.However,the trend of BG:AKP and NAG:AKP showed single-peak change,and the maximum value appeared in the 25years of enclosure.?6?There was a significant or extremely significant positive correlation among the activities of BG,NAG and AKP.The activity of BG was positively correlated with organic carbon,total nitrogen and microbial nitrogen,and positively correlated with soil moisture and microbial biomass carbon,but negatively correlated with soil bulk density and nitrate nitrogen.The activity of NAG was positively correlated with microbial biomass carbon,positively correlated with microbial biomass nitrogen and total nitrogen,and negatively correlated with nitrate nitrogen.The activity of AKP was positively correlated with organic carbon and total nitrogen,but negatively correlated with available phosphorus.