Spatial-Temporal Distribution And Influencing Factors Of Soil Enzyme Activity In The Typical Karst Fragile Ecosystems

In this study,five enzyme activities,such as urease,invertase,alkaline phosphatase,amylase and protease,were studied in the rocky desertification ecosystem of the Guanling-zhengfeng Huajiang karst plateau in Guizhou Province.The temporal and spatial distribution characteristics of soil enzyme activities in different seasons,soil profiles,slopes,aspect,elevation and land use patterns in karst ecosystems were investigated.The response of five soil enzyme activities to the succession of rocky desertification was analyzed.The influence factors of soil enzyme activity in karst ecosystem were further studied by redundancy analysis.The main findings are as follows:(1)Temporal and spatial distribution characteristics of soil enzyme activity in Karst ecosystem.The variation characteristics of enzyme activities in five kinds of soil were different in different time and space.In time,there was no significant difference in enzyme activity and complex enzyme activity between April-May and September-October(P>0.5).In space,only sucrase,amylase,protease and soil synthetic enzyme activities were significantly different in soil profile(P<0.5).However,the activities of different enzymes and synthetic enzymes 0~5 cm were higher than that of 5~10 cm.In the slope range of 0~60°,there was no significant difference in the activity of five enzymes and the activity of soil complex enzyme(P>0.5),and only showed a relatively high activity in the slope of 0~30°.There were only significant differences in urease activity among 5 different slope directions(P<0.5).The activities of the five enzymes were stronger in the East,South and North Slope directions.There were significant differences in urease,alkaline phosphatase,amylase and synthetase activities between 700 and 1200 m altitude(P< 0.5),but no significant differences in sucrase and protease activities(P>0.5),and the activities of the five enzymes were the highest at 801~900 m.Under different land use patterns,there were significant differences in activities of five enzymes and synthetical enzymes(P< 0.5).Woodland has significant advantages in soil enzyme activity under six land cover,especially in primary forests.In the future ecological construction,afforestation on the basis of protecting existing forest land can be an important measure for vegetation restoration and reconstruction in the area.(2)Response of soil enzyme activity to rocky desertification succession in karst ecosystem.Under different rocky desertification grades,only urease and sucrase had significant difference with the succession of rocky desertification(P<0.5),which was more sensitive to the succession of rocky desertification.With the enhancement of the degree of rocky desertification,the change characteristics were decreased first and then increased,which was consistent with the change characteristics of synthetic enzyme activity.In different rocky desertification environments,different enzyme activities have different responses to the succession of rocky desertification.The response of enzyme activity in non-rocky desertification and potential rocky desertification environment was stronger than that in non-rocky desertification environment.Redundancy analysis showed that invertase,alkaline phosphatase and amylase could well reflect the environmental conditions of non-rocky desertification and potential rocky desertification,and there was a positive correlation among them.Therefore,in the treatment of rocky desertification,the enzyme activity index with strong relative response can be selected as a reference for specific environmental conditions.(3)Factors affecting soil enzyme activity in Karst ecosystem.The effect of soil physical and chemical environmental factors on soil enzyme activity was greater than that of space environmental factors.Redundancy analysis showed that total nitrogen,carbon-nitrogen ratio,nitrogen-phosphorus ratio and water content were the four important factors that affected the enzyme activities of five soils.The total nitrogen content of soil is the main factor affecting the protease activity of karst rocky desertification ecosystem.The ratio of nitrogen to phosphorus is an important factor affecting the activity of alkaline phosphatase.The carbon to nitrogen ratio may be one of the important inhibitors of these five enzyme activities.Nitrogen and its ecological stoichiometry may present better variation of enzyme activity than other nutrient factors.