Abstract: Aims Soil nitrogen mineralization, nitrification and microbial nitrogen immobilization are key processes in soil nitrogen cycle, which have an important impact on soil nitrogen supply. Exploring the spatial variations in soil nitrogen transformation rates of forest may contribute to in-depth understanding of forest soil nitrogen dynamics and forest ecosystem productivity. Methods In this study, we integrated and analyzed 685 observations from 78 published papers, and aimed to analyze the rate characteristics of soil gross nitrogen mineralization, gross nitrification and microbial nitrogen immobilization of forest ecosystem and the main influencing factors. Important findings The results showed that: (1) The average rate of soil gross nitrogen mineralization, gross nitrification and microbial nitrogen immobilization of forest ecosystem were 6.65±0.61、1.99±0.21 and 8.10±1.45 mg N kg-1d-1, respectively. (2) The soil gross nitrogen mineralization rate and gross nitrification rate differed significantly among various forest types. Higher gross nitrogen mineralization rates were observed in tropical forest and temperate coniferous forest, while lower rates in subtropical broad-leaved forest and subtropical coniferous forest. The microbial nitrogen immobilization rates were higher in temperate coniferous and broad-leaved mixed forest, but was lower in subtropical coniferous and broad-leaved forest. (3) Soil gross nitrification rates exhibited no significant differences among various forest types. (4) The spatial variations in soil gross nitrogen transformation rates were main regulated by soil total nitrogen content and microbial biomass. Overall, the gross nitrogen transformation rates exhibited large spatial variability across global forest, and they were mainly affected by substrate supply and microbial biomass.

Key words: forest ecosystem, soil nitrogen cycle, gross nitrogen mineralization rates, gross nitrification rates, microbial nitrogen immobilization rates.