关键词: 微生物氮利用效率, 氮添加, 生态化学计量, 同位素示踪, 森林

Abstract: Aim Microbial nitrogen use efficiency (NUE) refers to the ratio of nitrogen used by microorganisms for growth to total organic nitrogen absorbed. It is a key factor in regulating the soil nitrogen cycle. The 18O-H2O method and eco-enzyme stoichiometric model are commonly used to estimate microbial NUE. However, research on how nitrogen enrichment affects microbial NUE in forest soils is still limited, which would affect the accurate prediction of soil nitrogen supply. Methods In this study, we sampled the soils from subtropical Castanopsis faberi forests and used urea to simulate atmospheric nitrogen deposition. In total, three treatments were set up, including control (CT, 0 kg N hm-2 a-1), low nitrogen (40 kg N hm-2 a-1), and high nitrogen (HN, 80 kg N hm-2 a-1). The 18O-H2O method and eco-enzyme stoichiometric model were used to compare the differences in soil microbial NUE under different nitrogen enrichment levels. Soil physicochemical properties, microbial biomass, extracellular enzyme activity, and stoichiometric imbalance were also measured to explore the factors that influencing the response of microbial NUE to nitrogen enrichment. Important findings The results showed that the microbial NUE obtained by different methods decreased with the increase of nitrogen enrichment. The vector angle values of different nitrogen treatments were all greater than 55°, which indicated that soil microorganisms in this study area were generally limited by phosphorus, but nitrogen enrichment did not worsen the phosphorus limitation. On the contrary, nitrogen enrichment has a significant negative effect on microbial carbon and nitrogen imbalance, and there was a positive relationship between microbial NUE and microbial carbon and nitrogen imbalance. In summary, nitrogen enrichment may be detrimental to soil nitrogen storage in subtropical forests. To improve this situation, it is recommended to further regulate soil ecological stoichiometric balance.

Key words: microbial nitrogen use efficiency, nitrogen addition, ecological stoichiometry, isotope labeling, forests