关键词: 氮沉降, 氮循环, 草地生态系统, 微生物

Abstract:

The intensification of human activities and the use of fossil fuels has increased atmospheric nitrogen deposition， which has a significant impact on the nitrogen cycling processes of terrestrial ecosystems， thus affecting ecosystem productivity and stability. Grasslands， are an important component of terrestrial ecosystems， and in many cases are subject to resource loss and nutrient imbalance due to human overuse and lack of awareness of protection needs， in which case the development of animal husbandry enterprises can be severely limited. It is highly relevant to explore the influence of nitrogen deposition on nitrogen cycles of grassland ecosystems for rational development of policy and practice with respect to utilization of grassland resources. This paper tracks published research results at home and abroad and a key finding is that most nitrogen addition inhibits biological nitrogen fixation processes， promotes nitrification， denitrification and mineralization in soils， inhibits the activity of nitrogen fixing microorganisms， and increases the abundance of ammonia-oxidizing bacteria of nitrifying microorganisms and expression of functional genes of denitrifying microorganisms， such as nirK， nirS， nirG and nosZ. However， the responses of the soil nitrogen cycle to nitrogen deposition in a few studies differed from the above due to differences in nitrogen nutrition and nitrogen application measures in a grassland environment. Through summarizing the existing studies， we found that： 1） The effects of nitrogen deposition on the nitrogen cycle differ between studies due to different soil background nutrient levels and nitrogen absorption thresholds； 2） Microorganisms are important participants in the soil nitrogen cycle， and the responses of microorganisms to nitrogen addition differ with different nitrogen application time， frequency and quantity. 3） The various steps of the nitrogen cycle in soils are closely coupled and influence each other， but most of the existing studies only focus on a particular step， and therefore the results do not provide comprehensive insight. Therefore， in future studies， it will be necessary to pay more attention to the study of soil nitrogen cycle microbial changes under particular nitrogen supply conditions in grasslands with different nutrient levels， and consider the multi-step coupling relationship， which is very important to the improvement of grassland ecosystem function and reduction of the threat caused by nitrogen loss from the environment.

Key words: nitrogen deposition, nitrogen cycling, grassland ecosystem, microorganism