| The nitrogen cycle is a key component of global biogeochemical cycles,with nitrification being a central step.Ammonia oxidation,as the first and rate-limiting step of nitrification,is mainly driven by ammonia-oxidizing bacteria（AOB）and ammonia-oxidizing archaea（AOA）carrying the ammonia monooxygenase gene（amoA）,converting ammonium nitrogen to nitrite nitrogen and releasing the greenhouse gas N2O.Ammonia oxidation is an important source of N2O emissions,exacerbating the greenhouse effect.The Qilian Mountains are located at the transition zone between the cold high-elevation region of the Qinghai-Tibet Plateau and the northwest desert area,featuring unique geographic and climatic characteristics that can indirectly influence nitrogen cycling in ecosystems by affecting microbial distribution and activity.However,it is still unknown how spatial climatic changes in the Qilian Mountains affect the structure and function of ammonia-oxidizing microbial communities in Picea crassifolia forests;the ammonia oxidation and N2O emission capacities of AOA and AOB have not been conclusively determined.Therefore,this study employs high-throughput sequencing,quantitative PCR,and microcosm cultivation techniques,combined with climatic factors and soil physicochemical properties,to investigate the community structure and function of ammonia-oxidizing microorganisms in Qilian Mountain Picea crassifolia forest soils.The main findings are as follows:（1）In terms of spatial distribution（longitude and latitude）,environmental factors such as the carbon-to-nitrogen ratio,annual mean temperature,and total nitrogen effectively distinguished sampling sites.The carbon-to-nitrogen ratio was significantly negatively correlated with nitrite and nitrate nitrogen,suggesting that it may be a key factor influencing the structure and function of ammonia-oxidizing communities.Meanwhile,it exhibited a significant quadratic relationship with annual precipitation,with a"U"-shaped function graph.（2）The abundance of AOA amoA genes was significantly higher than that of AOB.The abundance of AOA and AOB amoA genes was significantly negatively correlated with the carbon-to-nitrogen ratio,nitrite nitrogen,and nitrate nitrogen,and exhibited a significant quadratic relationship with annual precipitation,with an inverted"U"-shaped function graph.Conductivity,elevation,and total carbon were significantly negatively correlated with the abundance of AOA amoA genes,while total nitrogen and annual precipitation were significantly positively correlated with the abundance of AOB amoA genes.（3）The dominant genera of AOA included Nitrosoarchaeum（35.71%）and Nitrososphaera（24.57%）.The dominant genus of AOB was Nitrosospira（99.87%）.Annual precipitation and carbon-to-nitrogen ratio had significant effects on community diversity.Soil moisture content,total nitrogen,total carbon,soil organic carbon,and p H value were the main environmental factors influencing community composition.（4）The abundance,diversity,composition,and network relationships of AOA and AOB amoA genes all influenced ammonia oxidation potential and N2O emission fluxes,but they were mainly determined by amoA gene abundance,with a greater impact from AOB amoA genes.（5）Spatial climatic changes in the Qilian Mountains,such as annual precipitation and mean temperature,can indirectly affect the structure and function of ammonia-oxidizing microbial communities through soil physicochemical properties.Moderate precipitation decreases the soil carbon-to-nitrogen ratio（increasing nitrogen availability）,thereby enhancing the activity of AOA and AOB communities.AOA and AOB exhibit different responses to temperature;annual mean temperature indirectly negatively affects the AOA community structure through conductivity,while directly positively affecting the AOB community structure.Additionally,changes in soil properties due to elevation also impact the structure of AOA and AOB communities,with soil nutrients having a positive effect on AOB community structure and a negative effect on AOA community structure.Conductivity only negatively affects the AOA community structure.The research findings show that:（1）Spatial climatic changes in the Qilian Mountains can indirectly influence the structure and function of ammonia-oxidizing microbial communities（ammonia oxidation and N2O emissions）through soil properties,and ammonia-oxidizing microorganisms exhibit different responses to annual precipitation,mean temperature,and elevation.（2）The community structure of AOA and AOB（amoA gene abundance,richness,composition,and network relationships）can influence their function,but the impact of the AOB community structure on the function is greater,mainly determined by amoA gene abundance.This study deepens our understanding of nitrogen cycling in the soil of this ecological region,enhances our knowledge of the response of ammonia-oxidizing microorganisms to environmental changes,and elucidates the intrinsic relationships between climate,soil properties,and ammonia-oxidizing microorganisms.Consequently,it enables better assessment of the impact of spatial climatic changes on the nitrogen cycle in Qilian Mountain Picea crassifolia forest ecosystems,and contributes to providing a theoretical basis for ammonia-oxidizing microorganism research under climate change. |
