Soil Extracellular Enzyme Activities And Their Controlling Factors In Typical Karst Ecosystems,Southwest China

Soil organic matter decomposition is the main source of atmospheric carbon dioxide(CO2),and it is also a key step in the circulation of carbon,nitrogen and phosphorus in the ecosystem.The organic matter in the soil needs to pass through the extracellular enzyme(unless otherwise specified,the soil enzyme referred to below refers to the extracellular enzyme)depolymerization(Depolymerization)to produce small molecules or single molecules of organic matter,the microbial can directly absorb the use of soil carbon,Nitrogen,phosphorus and other substances in the follow-up process can be carried out smoothly.Because of this,the soil enzyme-mediated macromolecule organic matter depolymerization of this step is often a soil carbon,nitrogen,phosphorus cycle of the restrictive link.It can be seen that soil enzymes play an important role in the circulation and energy flow of ecosystems.It is important to understand the soil enzyme activity in understanding the biogeochemical cycle ofcarbon,nitrogen and phosphorus in ecosystems.The karst ecosystem is an important part of the Earth's surface system.Due to the particularity of its geological background,the biochemical cycling cycle of karst ecosystem exists specificity,which may lead to the activity of soil extracellular enzyme and its main control factor is different from other ecosystems.However,there is a lack of research on the activity of extracellular enzyme and its main controlling factors in the typical ecosystem of karst mountain area in southwest China.In this study,the effects of carbon,nitrogen and phosphorus on the extracellular enzyme activities and their main controlling factors in different vegetation restoration stages(farmland,grassland,shrub and secondary forest)were studied in this typical karst ecosystem.On this basis,A comparative study was conducted on the activity of extracellular enzynes in typical karst and adjacent non karst forest soils.The main conclusions of the study are as follows:(1)the activities of three hydrolases(i.e.?-Glucosidase,a-D-1,4-Cellobiosidase,and P-1,4-Xylosidase)increased following the agricultural abandonment(secondary forest>shrubland>grassland>cropland),but the oxidase(i.e.Peroxidase)activity had no significant change.The reasons for this differential response may due to the preferential utilization of labile C by microbe.That is,after agricultural abandonment microbe tends to use the labile C and thus did not increase the input of oxidase for decomposing passive C because of the high soil C stabilization in karst area.The results suggest that agricultural abandonment may increase the accumulation of passive C pool in karst area.In karst area,after returning farmland with vegetation restoration,the nitrogen cycle enzyme activity increased,and the polymerization is the limiting step of nitrogen transformation.The activity of phosphatase was related to soil pH and exchangeable magnesium ion,but had no significant correlation with other physical and chemical properties.The comprehensive analysis showed that the exchangeable magnesium ions in karst area had positive effect on acid phosphatase,the results showed that there was no significant correlation between the soil physicochemical indexes and the phosphatase activity in the karst area except the pH and the exchangeable magnesium ion.(2)In the karst and non karst areas,the enzymatic activity of the karst area(alkaline calcareous soil)was generally higher than that in the non-karst area(acidic red soil),except for acid phosphatase and several Chitinase activity,the other eight kinds of enzyme activities were significantly higher in the karst area than in the non-karst area.The control factors of the enzyme activities of the two soil types were also different.The kinetics of the karst area was more concentrated than that of the non-karst area.(3)The relative contribution of tree species,soil physical and chemical properties and soil type explanatory variables to soil enzyme activity were analyzed by variance method.The results showed that the explanations of the three groups explained 62.6%of soil enzyme activity variation.Among them,soil physical and chemical properties explained 58.2%of soil enzyme activity variation,soil type explained 38.7%of soil enzyme activity variation,and tree species explained 27.8%of soil enzyme activity variation.Three groups of variables exist interaction,the three common interpretation of the part of 17.8%.When the two common explanations were removed,the soil physical and chemical properties explained 23.4%of the variation of soil enzyme activity,3.9%of the soil enzyme activity variation and 0.9%of the soil enzyme activity.