Effects Of Vegetation On Soil Extracellular Enzyme Activity In Erosive Environment

The Loess Plateau is characterized by weak ecological environment,poor soil fertility,uneven spatial distribution of nutrients and deterioration of microbial ecosystem due to soil erosion.During the process of vegetation restoration,both the aboveground and underground ecosystems have changed and the soil conditions have been improved.Soil microbial and enzyme activities are highly correlated with soil properties and participate in organic matter metabolism,thus affecting nutrient availability,accumulation and mineralization,which can be used as a comprehensive index to measure soil nutrient status and element imbalance.Accordingly,this study selected five small watershed on the loess plateau（erosion and deposition）Settings have different terrain vegetation and vegetation experimental plot,determination of some soil physical and chemical properties and extracellular enzymes,probes into the extracellular enzyme activity and soil measurement ratio on the response of the vegetation,and its relationship with terrain,location,and further establish the soil microbial nutrient limitation in the study area,the key driving factors of soil nutrient limitation and the contribution of vegetation to soil biochemistry were also discussed The main results are as follows:（1）Vegetation improved the activities of soil carbon（CBH and BG）,nitrogen（NAG and LAP）and phosphorus（ALP）cyclase enzyme activities in erosion and deposition area.The effect of vegetation on soil P cycle enzyme was greater than that of C cycle enzyme and N cycle enzyme.The enzyme activity of P,C and N cyclase in vegetation plot was 30.0,10.0and 9.0 nmol·g^-1·h^-1 higher than that in non-vegetation plot,and that in erosion area was 16.0,5.0 and 5.0 nmol·g^-1·h^-1 higher,respectively.The effect of vegetation on soil enzyme activity in the surface layer was greater than that in the deep layer,and the CBH and BG enzyme activities in the deeper soil layer at 20 cm had little response to the vegetation,while the ALP enzyme activity in the deep soil still increased significantly.（2）Soil erosion-deposition significantly affected the spatial distribution of soil C,N and P cycling enzymes,and the response of enzyme activity to vegetation in the deposition area was greater than that in the erosion area.The difference of C,N and P enzyme activity in the deposition area were 95.3%,71.3%and 89.4%higher than that in the erosion area,respectively.The difference of the activities of the three cyclic enzymes in the erosion and deposition area decreased gradually among the plots with or without vegetation in the deep layer.（3）Vegetation increased the activities of C and N cyclic enzymes in the eroded and depositional areas of Shenmu,Changwu and Guyuan.The activities of C and N cyclases in the surface of Suide erosion area were increased by 77.6%and 42.4%,respectively,and decreased by 64.7%and 64.2%,respectively,in the deposition area.In the Ansai sedimentary area,the surface C cyclic enzyme activity increased under the action of vegetation,but decreased in the eroded area.Vegetation increased the activity of P cycling enzyme in Shenmu and Ansai,and decreased the activity of ALP enzyme in surface layer of soil erosion area and Suide sedimentary area by 13.1% and 45.0% under the effect of vegetation.（4）The effect of vegetation on the average C cyclic enzyme activity in different sites was greater in the deposition area than in the deposition area.Except Shenmu,the average N cyclic enzyme activity in the deposition area was greater than that in the erosion area,and the average P cyclic enzyme activity in the erosion area of Ansai was greater than that in the deposition area,while the other sites were on the contrary.（5）There were significant differences in extracellular enzyme stoichiometric ratio between different erosion environments（erosion zone and deposition zone）and vegetation-free zones.The C:N enzyme activity ratio in the Guyuan deposit area without vegetation was 44.5%higher than that in the area with vegetation,and the difference was significant.The activity of C:P enzyme in the Suide sedimentary area was 37.9%higher than that in the non-vegetation sedimentary area,and 35.7%lower than that in the Guyuan sedimentary area,showing significant differences.The N:P enzyme activity ratio in the non-vegetated plot was 31.5%lower than that in the vegetated plot in Suide sedimentary area,and the difference was significant.（6）SOC and TN were the main factors affecting the activities of C and N cyclic enzymes and the C:P enzyme measurement ratio,while soil texture（silt and sand content）and climatic conditions（MAT）largely determined the soil ALP enzyme activity and C:N and C:P enzyme activity ratio.It was found that soil microorganisms in five small watershed of the Loess Plateau were restricted by C and P,and the degree of P restriction was greater,which deviated from the global 1:1:1 enzyme metering ratio steady state.The microbial community of the non-vegetated plots in the sedimentary area has the lowest relative C and P limits,which may be caused by the low competition of soil microbial nutrients.