Effects Of Warming And Exogenous Nitrogen Addition On Soil Physical And Chemical Properties And Enzyme Activities In Active Layer Of Permafrost In Daxing'an Mountains

With the global warming and the deposition of a large number of nitrogen compounds from the atmosphere into the terrestrial ecosystem,the original material circulation balance and soil enzyme activity will be greatly threatened.Active layer is the transition layer of water and heat exchange between permafrost and atmosphere.The change of active layer not only affects the water and heat characteristics of soil,but also has important influence on energy exchange,carbon and nitrogen cycle,ecosystem and climate system.The study on the response of soil enzyme activities to global warming and atmospheric nitrogen deposition in the active layer can provide a theoretical basis for predicting the response direction of soil enzyme activities to climate warming and nitrogen deposition in different depths of the active layer in the permafrost region.In this study,two temperatures and four nitrogen application rates were set by indoor simulation method to conduct experiments on soil enzymes and basic physical and chemical properties of the soil.The research results showed that:(1)The pH values had little vertical change and were all in the acidic state;The closer the soil moisture content is to the permafrost,the greater the value is.The soil temperature decreased with the increase of soil depth,and the bottom soil temperature was close to 0?.The soil total nitrogen content increased with the increase of sampling depth,while the ammonium nitrogen content decreased with the increase of sampling depth,and the vertical distribution of nitrate nitrogen in the active layer decreased slightly.The total organic carbon content decreased from top to bottom in depth,and the soil soluble organic carbon content increased as the soil was closer to the surface.Soil total phosphorus content did not vary significantly in depth.(2)The vertical spatial distribution characteristics of soil enzyme activities: the activities of sucrase,?-glucosidase and acid phosphatase decreased significantly in depth,but the changes of soil urease activities were not significant in the whole active layer.Temperature,ammonium nitrogen,nitrate nitrogen and total organic carbon were positively correlated with the activities of the four enzymes,while soil water content,total nitrogen,total phosphorus and soluble organic carbon were negatively correlated with the activities of the four enzymes.Soil ammonium nitrogen,total organic carbon,nitrate nitrogen and soil temperature were the main factors affecting the activities of soil sucrose,?-glucosidase,urease and acid phosphatase,which could explain 36.4%,27.4%,15.9%and 10.1% of the changes of soil enzyme activities,respectively.(3)The effects of indoor simulated temperature and the addition of exogenous nitrogen on soil basic physical and chemical indexes were studied.The results showed that except for the surface soil,the soil total organic carbon content decreased with the increase of temperature,and the increase of temperature had different promoting effects on the soil soluble organic carbon content in the whole active layer.However,temperature had no obvious effect on soil total nitrogen and ammonium nitrogen contents.The soil total phosphorus content first increased and then decreased with the increase of temperature.Under 5?,soil total organic carbon,soil soluble organic carbon and soil total phosphorus were inhibited by the three gradient nitrogen application rates.The inhibition effect of low nitrogen on soil total organic carbon and soil total phosphorus was significantly higher than that of high nitrogen.Under 15?,the three nitrogen application concentrations inhibited the contents of soil total organic carbon and soluble organic carbon,but promoted the contents of soil total phosphorus.Warming,nitrogen application and their interaction had little effect on soil p H.Soil total organic carbon content decreased under the effects of temperature increase and nitrogen application,and the inhibition effect increased with the increase of nitrogen application concentration,and the content of soil soluble organic carbon increased,which inhibited the total phosphorus content in surface soil,but promoted the total phosphorus content in bottom soil.(4)Laboratory simulation experiments showed that soil sucrase was promoted by different temperatures;Soil urease activity was promoted at 5?,but inhibited at15?.The effect of temperature on soil acid phosphatase activity was opposite to that of soil urease.The activity of ?-glucosidase in the surface layer and bottom layer was promoted at 5?,but the activity of ?-glucosidase was inhibited at other temperatures.Under 5?,the activities of soil sucrose and soil acid phosphatase were increased by three nitrogen inputs,but the activities of ?-glucosidase and soil urease were decreased,but the activities of surface soil sucrose and ?-glucosidase in 0-20 cm were different.Under 15? :On the whole,the activities of sucrase,?-glucosidase and soil urease were increased with the addition of nitrogen at different concentrations,but the effect of high nitrogen input on soil urease was opposite,and the activity of soil acid phosphatase was decreased with the addition of nitrogen.The activities of ?-glucosidase,urease and acid phosphatase were increased under the condition of increasing temperature and low nitrogen,but the effects on sucrase were opposite.Nitrogen increased the activity of sucrase,urease and acid phosphatase,but decreased the activity of ?-glucosidase.Increasing temperature and high nitrogen increased sucrase and ?-glucosidase,but inhibited urease acid phosphatase.