Dynamic Characteristics And Influencing Factors Of Soil Respiration In An Alpine Swamp Meadow Under The Conditions Of Warming And Nitrogen Application

With the warming of global climate and the aggravation of nitrogen deposition,the related research has become a hot spot.The fifth report of the Intergovernmental Panel on Climate Change(IPCC)shows that the warming has reached 0.85?0.89?in the past 100years.At the same time,due to the rapid development of industry,agriculture and cities,China's nitrogen emissions have been increasing since the 1980s.Although China's Grassland Ecosystem only accounts for 6-8%of the world's total grassland area,its carbon accounts for9-16%of the world's total grassland carbon,making a huge contribution to the world's carbon storage.As an important part of global carbon cycle,soil respiration is closely related to global change.Small changes in soil respiration may cause great changes in atmospheric carbon dioxide concentration.The alpine wet meadow ecosystem in the fenghuoshan area in the hinterland of the Qinghai Tibet Plateau is selected in this study.As the highest plateau in the world,the Qinghai Tibet Plateau is vulnerable to global change due to the harsh environmental conditions.Therefore,the study of soil respiration and its influencing factors under warming and nitrogen application can provide a reference for predicting the response of soil carbon emission and cycling mechanism to global change.The experiment uses open-top heating chambers and artificial nitrogen addition to simulate climate warming and atmospheric nitrogen deposition.It measures soil respiration rate and temperature and moisture,and collects soil to determine microbial biomass carbon and nitrogen and soil nutrients,aiming to explore alpine swamps.The response of meadow soil respiration,microbial status and soil nutrients to warming,nitrogen application and their interactions.The main results are as follows:(1)The temperature increase,nitrogen application,and the coupled treatment of temperature increase and nitrogen application all changed the soil respiration rate,and the soil respiration rate under different treatments all showed consistent seasonal changes,that is,the soil respiration rate during the breeding period was higher than that during the regreening period.Withered.Warming of different magnitudes all showed a promotion effect on the soil respiration rate in the regreening and withering periods in 2018,but with the increase of the warming time,the significance of this promotion was reduced in 2019.The high-amplitude temperature increase treatment during the breeding period significantly increased the soil respiration rate during the two years,while the low temperature increase had no significant effect on the soil respiration rate in 2018,but it significantly increased the respiration rate in2019.The application of different concentrations of nitrogen fertilizer showed similar trends in the soil respiration rate during the turning green period and the withered period,and both increased the respiration rate significantly.Low-concentration nitrogen application during the breeding period did not significantly affect the soil respiration rate during the two-year period,and high-concentration nitrogen application did not significantly affect the respiration rate during the breeding period in 2018,but the respiration rate increased in 2019.The soil respiration rate in different months of the growing season was significantly higher than the corresponding control treatment under the treatment of increasing temperature and applying nitrogen.(2)There is an exponential relationship between soil respiration and soil temperature,and as the soil temperature increases,the respiration rate shows an upward trend.For different temperature-increasing nitrogen applications and their interaction treatments,soil temperature can explain 57.6%?80.8%seasonal changes in soil respiration rate.It has a quadratic function relationship with soil moisture,and soil moisture can explain 31.3%-79.3%of the variation of soil respiration rate under different treatments.The explanation of soil temperature on soil respiration rate is higher than that of soil moisture,which indicates that soil temperature is the main factor of soil respiration change in this study area.Soil temperature and soil moisture can always explain most of the variation of soil respiration.And as the treatment methods become more complex,the explanation of soil respiration by a single hydrothermal factor decreases,and soil temperature and soil moisture in different levels of warming and nitrogen treatment jointly explain 73.8%to 91.7%of the change in soil respiration rate.(3)Fitting with the Van't Hoff model shows that the temperature sensitivity of soil respiration under different temperature-increasing nitrogen application and its interaction treatments is lower than that of the control treatment.The temperature sensitivity coefficient of the control plot is 7.85.Under nitrogen treatment,the Q₁₀values were 4.31 and 4.62,respectively.The Q₁₀values were 4.81 and 6.88 under the low-amplitude and high-amplitude warming.The Q₁₀values were the lowest under the simultaneous application of nitrogen and the temperature was 4.22.(4)The soil microbial biomass carbon and nitrogen under different treatments showed similar seasonal differences,and the soil microbial biomass carbon content during the breeding period was higher than that in the green and yellow periods.Different warming treatments during the rejuvenation period increased the soil microbial biomass carbon and nitrogen content in the 0-10cm soil to a certain extent,but showed different effects on the soil microbial biomass carbon and nitrogen in the 10-20cm soil layer,and the microbial biomass carbon content had no effect even decreased,while the microbial biomass nitrogen content was significantly increased(p<0.05).Nitrogen application treatment showed a certain degree of promotion effect on soil microbial biomass carbon and nitrogen,but in 0-10cm soil layer,with the increase of concentration,the promotion effect of nitrogen application on MBC decreased,and high concentration nitrogen application treatment had effect on surface MBC.The content showed no influence or even inhibition.In the 10-20cm soil layer,the effect of nitrogen application on the MBC content showed obvious seasonal changes.Under different concentrations of nitrogen,the MBC content in the 10-20cm soil layer decreased to a certain extent during the regreening period,while the reproduction period Both the yellowing period and the yellowing period have improved to a certain extent.The high-concentration nitrogen application significantly promoted the microbial biomass nitrogen content in the 10-20cm soil layer during the regreening period and the reproduction period(p<0.05).Simultaneous temperature increase and nitrogen application significantly promoted the microbial biomass carbon during the reproductive period and the yellowing period,and the promotion effect was more significant with the increase of soil depth,while the promotion effect of temperature increase on the microbial biomass carbon during the greening period was not obvious,and even increased with the soil depth showed an inhibitory effect.The soil microbial biomass nitrogen was significantly increased during the reproductive period under the treatment of increasing temperature and nitrogen,and the microbial biomass nitrogen content in the turning green period and the withering period had no significant effect or even decreased.And different treatments changed the carbon-nitrogen ratio of the microbial biomass.(5)Redundant analysis of soil physical and chemical properties and soil respiration shows that the physical and chemical properties have an impact on soil respiration.The soil respiration rate in the growing season is positively correlated with 0-10cm soil layer soil ammonium nitrogen and soil microbial biomass nitrogen during the two years,Is negatively correlated with soluble total nitrogen and soluble organic carbon.The respiration rate was positively correlated with soil microbial biomass carbon and nitrogen,soil ammonium nitrogen and organic carbon in the 10-20cm soil layer during the two years,and the microbial biomass carbon and nitrogen were positively correlated(p<0.05).At the same time,there was a significant positive correlation between soil respiration and ammonium nitrogen in the two layers of soil during the two years(p<0.05).