Short-term Responses Of Carbon And Nitrogen Allocation To Warming And Nitrogen Addition In Soil-vegetation System Of Alpine Swamp Meadow On The Qinghai-tibetan Plateau

Global warming and increased nitrogen?N?deposition have become the hot issues in domestic and international researches.According to the fifth assessment report of the IPCC,the average global temperature has increased by 0.85°C over the past 130 years.At the same time,due to the widespread use of industrial N and agricultural N fertilizers around the world,atmospheric N deposition has continued to increase.Due to the special environmental conditions,the alpine swamp meadow ecosystem on the Qinghai-Tibetan Plateau is sensitive to climate change.Global warming and increased N deposition could directly or indirectly affect soil nutrients,plant growth and its carbon?C?and nitrogen processes.As a result,the C and N cycle of the ecosystem has changed.In this study,an alpine swamp meadow on Fenghuo Mountain was taken as the research object,open-top chambers were utilized to generate an artificially warmed environment,and N fertilizer was applied to simulate N deposition.The changes of soil nutrients and their availability,the plant biomass production and allocation,and the C and N contents in plant were determined.Thus the influences of warming,N deposition,and their interaction on soil-plant C and N processes and plant biomass production were studied.To provide theoretical basis for revealing the response and regulation mechanism of soil-plant system C and N stoichiometry characteristics and plant biomass production to climate change.The main findings were as follows:?1?Warming,N application,and their interaction remarkably changed soil nutrient content and its effectiveness.During the greening period?June?and withering period?September?,both warming and N application significantly reduced soil ammonium N content,but the soil ammonium N in T₂ was not significant affected in September?P>0.05?.During the reproduction period?August?,soil ammonium nitrogen increased significantly?P<0.05?in warming and N application treatments.Except in the yellowing period?September?,warming combined with N application significantly increased the ammonium nitrogen content during the other periods of the growing season?June and August??P<0.05?.In T₁ and N application(N₅,N₁₀)treatments,soil nitrate nitrogen content decreased significantly.Except in the greening period,soil nitrate nitrogen content in T₂ were increased significantly?P<0.05?during the other periods.Meanwhile,warming combined with N application showed significant positive effects on soil nitrate nitrogen content throughout the entire growing season.The soil organic carbon content increased significantly with warming and warming combined with N application?P<0.05?;while under N application,the soil organic carbon content decreased significantly during the greening and withering periods?P<0.05?,and the reproduction period increased significantly.Under warming treatment,the total nitrogen content of the soil during the greening period decreased significantly and increased significantly in other periods;under N treatment,the total nitrogen content of the soil during the greening and withering periods decreased significantly,and the reproduction period increased significantly?P<0.05?;warming combined with N application showed a significant positive effect on soil total nitrogen content?P<0.05?.?2?Warming,N application,and their interaction remarkably changed plant biomass production and distribution.Warming,N application,and their interaction showed significant positive effects on the aboveground biomass of plants?P<0.05?.The response of plant underground biomass and total biomass to warming and N application were consistent,and both showed a significant increase under warming treatment;under N application and warming combined with N application,the underground biomass of the plant was significantly reduced in addition to the greening period?P<0.05?.At the same time,the root-shoot ratio of the plants was significantly reduced under the conditions of Warming,N application and warming combined with N application,and the biomass distribution of plants changed significantly.?3?Warming,N application,and their interaction remarkably changed the carbon and nitrogen content in plants.The effects of each treatment on the C content in the aerial part of the plant were generally not obvious,and the C content in the root system was significantly reduced.At the same time,the N content in the aerial part of the plant decreased and then increased under the Warming;both N application and warming combined with N application showed a significant positive effects on the N content of the aerial part of the plant?P<0.05?,but the nitrogen application treatment had a more significant effect.At the same time,the N content of the plant roots showed a significant positive effect under the other treatments except that the N content was significantly reduced under the T₁ treatment.As a result,in addition to the C/N of the plants above ground increased significantly during the greening period,the C/N of the plants above ground and roots were significantly reduced in different periods and under different treatments,and the nutrient use efficiency of the plants changed.?4?Warming,N application,and their interaction remarkably changed the carbon and nitrogen content of litter.Except that the C content of litter under warming was significantly increased during the greening period?P<0.05?,the other periods decreased significantly.However,the content of litter C under N application and warming combined with N application treatment increased significantly during the greening and withering periods,and the reproduction period was obviously decreased,but the difference was more obvious when the warming combined with N application was applied at the same time.At the same time,both warming and warming combined with N application showed obvious negative effects on the N content of plant litter,and the N content of plant litter increased significantly under N application.In warming and warming combined with N application treatments,the C/N of plant litter increased significantly,but decreased significantly under N application,and the decomposition rate of plant litter changed.