Research On Soil Nitrogen Turnover And Its Response To Warming In Alpine Grassland

Global climate change is slowly changing the process of terrestrial ecosystems.Alpine meadow ecosystem is undergoing a greater degree of warming changes.Alpine grassland ecosystem,as an important part of the terrestrial ecosystem,is an ideal place and research object to study the response to climate change.Nitrogen is a necessary element for the growth of life,and the change of nitrogen supply will directly affect the productivity of the ecosystem.It is of great significance to explore the response of soil nitrogen content and nitrogen turnover process to temperature change.Based on this,this paper selected?Kangding,which is Sichuan Province as the study area of ?Hailuogou-Yajiagen?in?Gongga?Mountain,and set up four field experimental observation plots at the altitudes of?3800 m,?4000 m,?4100 m?and?4200 m.and 4200 m above sea level.Use Open-Top-Chamber?OTC?to simulate the warming experiment.Set up a comparative treatment under different elevations under natural conditions.Four soil samples from April,May,August and November were selected in the experiment to analyze the response of soil temperature,humidity,ammonium nitrogen and nitrate nitrogen to increasing temperature.At the same time,the¹⁵N isotope pool dilution method was used in the indoor cultivation experiment to study the total conversion rate of soil nitrogen in the alpine grassland ecosystem at 4000 m altitude.By comparing the differences between different soil treatments and different depths,the responses of soil temperature,humidity,ammonium nitrogen,and nitrate nitrogen to the variation of temperature and altitude gradient in the alpine grassland ecosystem were discussed.The¹⁵N isotope pool dilution method was used to explore some changes of soil nitrogen turnover rate caused by the increase of temperature,and further clarified the nitrogen cycle model in the alpine grassland ecosystem in the study area.Furthermore,it provides some theoretical basis for dealing with climate change in the nitrogen storage and nitrogen turnover process of the alpine meadow ecosystem in the future.The important conclusions of this study are as follows:?1?The warming treatment?OTC?can increase the temperature of each layer of soil?0-5 cm,5-10 cm?.The soil temperature under warming treatment at different elevations was significantly taller than that of?CK?under control treatment,and the soil temperature of the 0-5 cm soil layer was taller than that of the 5-10 cm soil layer.?2?The temperature increase has different effects on soil humidity.The temperature increase significantly reduces the soil water content of the 0-5 cm soil layer at 3800 m altitude in May,November,and 4000 m altitude in May.Under the temperature increase of 4000 m?OTC?0-5 cm the soil water content of the 5-10 cm soil,layer is significantly lower than that of its control?CK?.?3?Under the same altitude warming?OTC?and the control treatment,only the soil ammonium nitrogen content in the soil layer of 4000 m above sea level in?CK?showed a significant difference between different treatments,and there was a very significant difference in soil ammonium nitrogen content between the control treatment and the control treatment at a different altitude.Under the warming treatment,there was no significant difference between different elevations,but between different months at the same altitude,under the warming treatment,there were significant differences in soil ammonium nitrogen content between May and August,August and November at 3800 m altitude and 4100 m altitude between April and May,April and August.Under the control treatment,there were significant differences between April and May,May and August,May and November,and 4200 m altitude between April and the other three months.?4?There were significant differences in the nitrate-nitrogen contents of 3800 m and 4100 m,4000 m and 4100 m,4100 m,and 4200 m in OTC 0-5 cm soil under temperature increasing treatment.There were significant differences in soil nitrate content between 3800 m and 4200 m,4000 m and 4200 m,4100 m,and 4200 m in OTC 5-10 cm.Under the control treatment,there was no significant difference in soil nitrate content between 3800 m and 4000 m,except that there was a very significant difference in soil nitrate content among all elevations of CK 0-5 cm.?5?During the period of 1d-7d during the incubation period,the average mineralization rates of the soil in OTC0-5,5-10 cm,and CK0-5,5-10 cm soil layers were 31.6,16.7,and 28.8,12.5 mg /?kg ? d?,which shows that increasing temperature can promote soil mineralization rate.?6?During the incubation period of 1d-7d,the average nitrification rate of each soil layer was OTC0-5 cm:2.96 mg/?kg ? d?> CK0-5 cm:1.4 mg/?kg ? d?> OTC5-10 cm:0.58 mg/?kg ? d?> CK5-10 cm:0.4 mg/?kg ? d??7?The effect of soil nitrogen fixation was obvious.When the labeling solution was added for 1 d,47.3%,57.2%,45% and 51.3% of soil ammonium nitrogen was fixed in OTC 0-5,5-10 cm,CK 0-5 and 5-10 cm soil layers,and 19.1%,57.5%,24.7% and 76.9% of soil nitrate-nitrogen were fixed.