Response Of Soil Respiration And Soil Microbial Biomass Carbon And Nitrogen To Nitrogen Application In Alpine Forests Of Western Sichuan

Nowadays,the increase of global atmospheric nitrogen deposition has become very obvious.China has become the third largest nitrogen deposition area after Europe and America.The atmospheric N settlement on the eastern margin of the Qinghai-Tibet Plateau has gradually become apparent.As the main body of the second largest forest area in China,the high mountain forest of Sichuan has an irreplaceable role and position in regional climate regulation,soil and water conservation,water conservation and biodiversity conservation.Soil microbial biomass carbon and nitrogen and soil respiration are very sensitive to changes in environmental factors.Changes in environmental factors such as temperature,moisture and nutrients in atmospheric nitrogen deposition may affect biochemical processes such as microbial biomass and soil respiration in alpine soils.A material cycle and energy flow that affects the entire ecosystem.The areas with severe nitrogen deposition in China are mainly concentrated in the eastern part of China and the middle and lower reaches of the Yangtze River.Nitrogen deposition promotes soil respiration and microbial biomass increase in the area,but the results of different regional and ecosystem studies may be inconsistent.There are still many uncertainties in the effects of microbial and soil respiration,especially the lack of nitrogen-restricted alpine forest ecosystems in western Sichuan.Therefore,we raise the scientific question:whether nitrogen application promotes soil respiration and soil microbial biomass carbon and nitrogen in subalpine forest ecosystems.Based on this,we selected the Sichuan Redwoods?Larix mastersiana?forest in the high mountains of western Sichuan as the research object.,through four horizontal gradient soil nitrogen control experiments(CK:0 gm^-2a^-1,N₁:2 gm^-2a^-1,N₂:5 gm^-2a^-1,N₃:10gm^-2a^-1),The effects of simulated nitrogen deposition on soil respiration and soil microbial biomass carbon and nitrogen in subalpine forests were discussed.It was found that nitrogen application had no significant effect on soil pH value,soil temperature,soil water content,soil total carbon,soil total nitrogen and soil total phosphorus in Sichuan redwood forest.Nitrogen application on soil soluble carbon,soluble nitrogen and solubility in Sichuan redwood forest Phosphorus,soil ammonium and nitrate nitrogen have significant effects;nitrogen application has significant effects on soil microbial biomass carbon and nitrogen,soil respiration,heterotrophic respiration,and autotrophic respiration flux.Seasonal changes had significant effects on soil temperature,soil water content,soil total carbon,soil total nitrogen,and soil total phosphorus in the redwood forests of Sichuan.Seasonal changes in soil pH,soil soluble carbon,soluble nitrogen,soluble phosphorus and soil ammonium in the redwood forests of Sichuan Nitrogen and nitrate nitrogen had no significant effect;seasonal variation had significant effects on soil microbial biomass carbon and nitrogen ratio and soil respiration in Sichuan redwood forest.Correlation analysis found that soil respiration was significantly positively correlated with microbial biomass carbon and nitrogen and microbial metabolic quotient.Microbial biomass carbon and nitrogen were significantly positively correlated with temperature and significantly negatively correlated with humidity.The relationship between soil respiration rate and soil 10 cm temperature and humidity was fitted by general linear regression.It was found that soil respiration rate was significantly positively correlated with soil temperature,and was significantly negatively correlated with soil moisture?P<0.001?.Soil temperature under medium nitrogen level.The sensitivity coefficient Q10?2.82?was significantly higher than the control Q10 value?1.97?.In summary,nitrogen application has significant effects on soil microbial biomass carbon and nitrogen and soil respiration.Nitrogen application can promote soil total respiration,autotrophic respiration,heterotrophic respiration flux and soil microbial biomass carbon.Nitrogen increase,nitrogen application increased soil respiration flux by 11-15%,soil microbial biomass carbon increased by 5-9%,and soil microbial biomass nitrogen increased by 23-34%.Under the three nitrogen application gradients,the medium nitrogen level(5 g m^-2 a^-1)promoted soil respiration most significantly.Future atmospheric nitrogen deposition will likely promote soil respiration and carbon and nitrogen cycles and soil carbon emissions.