Responses Of Soil Respiration And Its Components To Nitrogen And Phosphorus Addition In Desert Steppe

Grassland ecosystems have huge carbon storage,and climate conditions and land management conditions have a great impact on the carbon cycle of grassland.The impact of nitrogen and phosphorus addition on the carbon cycle of grassland ecosystems has an important guiding significance for guiding grassland management.The dynamic characteristics of soil respiration under exogenous nutrient addition have an important significance for global climate change.This study focused on the desert grassland Stipa breviflora community and conducted a nitrogen and phosphorus nutrient addition experiment.The experimental treatments included CK control,nitrogen addition(10 g.m^-2.a^-1),phosphorus addition(8 g.m^-2.a^-1),and simultaneous nitrogen and phosphorus addition.To study the effect of nitrogen and phosphorus nutrient addition on soil physical and chemical properties throughout the growing season of vegetation,and the dynamic process of soil respiration throughout the growing season,and to explore the key driving factors of soil respiration,such as plants,soil,microorganisms,etc.The study revealed the impact of nitrogen and phosphorus addition on the dynamic change characteristics of soil respiration and its components（autotrophic respiration and heterotrophic respiration）during the growing season,explored the relationship between the soil temperature sensitivity coefficient(Q₁₀)and soil respiration and its components,and clarified the biological and abiotic key factors of nitrogen and phosphorus addition on soil respiration,It is expected to provide theoretical guidance for further understanding the carbon cycle process and services of natural desert grassland ecosystem,as well as grassland ecological restoration and management supply.The main research progress is as follows:（1）The addition of nitrogen and phosphorus enhances soil autotrophic respiration and weakens soil heterotrophic respiration.The respiration rate of soil respiration and its components showed an obvious single peak curve with time.The soil moisture in May and July at the beginning of growth was lower than that in other months.When the soil moisture was low,soil moisture instead of soil temperature became the key factor restricting soil respiration.The soil water content is higher in October at the end of the growing season.Because the soil temperature is lower,the soil respiration value is the lowest in the whole growing season;In general,nitrogen and phosphorus addition increased the rate of soil respiration.In August,nitrogen and phosphorus addition decreased the rate of soil heterotrophic respiration,while in October,nitrogen and phosphorus addition decreased the rate of soil heterotrophic respiration.The interaction between nitrogen and phosphorus addition has a significant promoting effect on soil heterotrophic respiration and a significant inhibitory effect on soil autotrophic respiration.The addition of nitrogen and phosphorus increased soil autotrophic respiration intensity,increased microbial biomass carbon and nitrogen,and decreased soil heterotrophic respiration intensity.（2）The soil temperature sensitivity coefficient showed a single peak curve with the growth period,and showed a quadratic linear relationship with soil respiration.The soil temperature during the growth season shows a single peak curve with the increase of months.Due to the joint influence of multiple factors,the overall variation of Q₁₀after nitrogen and phosphorus addition is irregular.The soil temperature reached its maximum value in August,while Q₁₀showed an opposite trend to the soil temperature,reaching its minimum value in Q₁₀in August;In July,September,and October,all treatments were able to increase Q₁₀.In May,only phosphorus addition increased Q₁₀,while in August,only nitrogen and phosphorus addition increased Q₁₀;Each treatment and the interaction of nitrogen and phosphorus addition had no significant effect on soil respiration and Q₁₀of its components.（3）Nitrogen and phosphorus addition affected the change of soil respiration by affecting microbial biomass carbon,underground biomass,glucosidase+cellobiose hydrolase and soil organic carbon.Both nitrogen and phosphorus addition and their interactions significantly affected soil organic carbon（SOC）,underground biomass（UGB）,glucosidase+cellobiose hydrolase（BG+CBH）,and microbial biomass carbon（MBC）.soil respiration and its components were significantly positively correlated with SOC,UGB,glucosidase+cellobiose hydrolase and MBC.After the addition of nitrogen and phosphorus,the change in SOC is a key factor causing changes in soil autotrophic respiration and soil heterotrophic respiration.The addition of nitrogen and phosphorus changes the living environment of microorganisms by increasing MBC and glucosidase+cellulose disaccharide hydrolase,improving their ability to assimilate nutrients,increasing their respiratory activity and promoting an increase in soil heterotrophic respiration rate.By increasing UGB,vegetation productivity is improved,and an increase in root respiratory activity of vegetation promotes an increase in autotrophic respiration rate.In conclusion,soil respiration in desert steppe of the Loess Plateau showed seasonal dynamic changes,and nitrogen and phosphorus addition increased the respiration rate of soil respiration and its components.In addition,the addition of nitrogen and phosphorus increased the intensity of soil autotrophic respiration,but decreased the intensity of soil heterotrophic respiration.The soil temperature sensitivity coefficient shows a unimodal curve change with the vegetation growth period.The effect of nitrogen and phosphorus addition on the soil temperature sensitivity coefficient is not regular,but in the late growth period,nitrogen and phosphorus addition increases the soil temperature sensitivity coefficient.The addition of nitrogen and phosphorus drives soil autotrophic and heterotrophic respiration by affecting soil organic carbon,underground biomass,glucosidase+cellobiose hydrolase,and microbial biomass carbon.