Responses Of Soil Enzyme Activity And Organic Carbon Distribution Characteristics To Warming And Nitrogen Application In Alpine Swamp Meadow On The Tibetan Plateau

Global climate change characterized by climate warming and increased atmospheric nitrogen deposition,which gradually attracted much attention of governments and scientific agencies attention.According to the prediction of the International Climate Change Committee,the global average temperature will rise by 1.2-4.0?by the end of the 21st century.At the same time,in the past few decades,the large-scale combustion of fossil fuels,the emission of industrial production waste gas and the large-scale using of nitrogen fertilizers have led to a proportional increase in nitrogen compounds in the atmosphere,resulted in a proportional increase in nitrogenous compounds in the atmosphere,a large amount of nitrides in the atmosphere sink into the terrestrial ecosystem through dry and wet nitrogen,breaking the original nitrogen balance in nature.With further economic development,climate warming and increased atmospheric nitrogen deposition will continue to affect soil enzyme activity and soil carbon and nitrogen cycles in the alpine swamp meadow ecosystem in the short term and in the future.Plants living conditions in swamp meadows is harsh.The swamp meadow ecosystem is more fragile than other ecosystems and is very sensitive to global climate change response and human interference.It is great significance to study the response of soil enzyme activity in alpine swamp meadow to global climate warming and increase in atmospheric nitrogen deposition,to study soil enzyme activity in the Tibetan Plateau ecosystem and to investigate the response of soil carbon and nitrogen cycle to global climate change.In this study,Open-top chambers?OTC?and artificial nitrogen application methods were used to simulate the two-factor test of temperature increase and nitrogen deposition.Using natural sample plot as a control?CK?,temperature-increasing?T₁,T₂?,nitrogen application(N₅,N₁₀)and temperature-increasing simultaneous nitrogen treatment?T₁N₅?,a total of 6 kinds of treatment.And aim of this study was to study the influences of elevated temperatures,nitrogen deposition,and their interaction on soil enzyme activities?including Catalase,invertase,urease,Amylase and cellulase?in alpine swamp meadows,as well as soil enzyme activity and organic carbon were studied relationship.The results show that:?1?Simulated warming has changed the air temperature and the 0-10 cm and 10-20 cm ground temperature increase significantly,but the effect of 10-20 cm ground temperature warming is weak,and the greater the temperature increase,the greater the temperature and ground temperature increase,indicating that the warming effect is good.At the same time,warming increases the soil water content,and as the soil layer deepens,the soil water content decreases.?2?Overall,warming promotes invertase and amylase activities throughout the growing season;however,warming has different effects on catalase and urease activities at different periods.Warming increases the activity of catalase during the greening period,but the effects of different warming ranges on the activity of catalase in other periods are not consistent;at the same time,warming inhibits the activity of urease during the greening and growing periods;the effects of enzymatic activity are inconsistent.Indicating that warming accelerates the growth of plants and accelerates the secretion rate of plant roots.At the same time,warming promotes the photosynthesis of plants and accelerates the rate of photosynthesis products like root transfer,thereby promoting the activity of invertase and amylase;simulated warming increases soil water content,high water holding capacity is not conducive to aerobic microbial activity,thereby reducing the activity of catalase.?3?Nitrogen application promoted the activities of catalase,invertase and amylase;at the same time,nitrogen application promoted the urease activity of 0-10 cm soil layer throughout the growing season,but the effect on cellulase activity was not consistent.Indicating that alpine swamp meadow has been in a low nitrogen state for a long time.Nitrogen application can alleviate the restrictive effect of nitrogen on plant growth,accelerate plant growth,accelerate plant root secretion rate,and then promote the activity of invertase and amylase;nitrogen application promotes urease activity,mainly to increase the concentration of urease reaction substrate after nitrogen application,and promote the urease activity.?4?Overall,the simultaneous application of warming and nitrogen application showed positive effects on amylase and cellulase activities throughout the growing season;positive effects on soil catalase activity during the greening and yellowing periods;while warming and simultaneous application The effect of nitrogen treatment on the activity of urease and invertase in different soil layers is inconsistent:increasing temperature and applying nitrogen treatment in the 0-10 cm soil layer promotes the greening and growing urease activities,but in the 10-20 cm soil layer only promotes the greening Urease activity in the period;temperature increase and nitrogen treatment promoted the activity of invertase in the growth period and the yellowing period in the 10-20 cm soil layer,but only promoted the invertase activity in the yellowing period in the 20-30 cm soil layer.?5?The temperature-increasing treatment increased the content of surface soil organic carbon,microbial biomass carbon and dissolved organic carbon.After nitrogen treatment,the dissolved organic carbon content decreased;the organic carbon content showed a downward trend during the greening period and the yellowing period,but increased during the growing season;the microbial biomass carbon content increased during the greening period and the growing season.The temperature increase and nitrogen treatment increased the organic carbon content,but reduced the dissolved organic carbon content;after the temperature increase and nitrogen treatment,the microbial biomass carbon content showed a downward trend during the greening period,but during the growth period and the yellowing period Upward trend.?6?The correlation analysis results of surface soil organic carbon pool and soil enzymes showed that soil organic carbon was significantly positively correlated with invertase and urease?P<0.01?;microbial biomass carbon,dissolved organic carbon and catalase were extremely significantly positive Correlation?P<0.01?,and microbial biomass carbon and cellulase showed a very significant positive correlation?P<0.01?,indicating that catalase,invertase,urease,cellulase and soil organic carbon components are closely related.These four enzymes are involved in the circulation of soil carbon elements,and the increase in enzyme activity can increase the content of soil organic carbon.