Abstract: Subtropical forest soil is a hot spot for fungal denitrification, which is an important pathway for the production of nitrous oxide (N₂O) in soils. However, the distribution pattern of the denitrifying fungal functional gene (FnirK) and its environmental drivers in subtropical Chinese fir plantations remain unclear. In this study, a total of 108 soil samples were collected from nine Chinese fir plantations in Fujian Province, and the abundance of FnirK gene was measured using real0time quantitative PCR. The results showed that the physicochemical properties and the abundance of FnirK gene exhibited significant spatial heterogeneity. The FnirK gene abundance in Guanzhuang State-owned Forest Farm, Shaxian County, Sanming City was the highest, at 19.75×10⁸ copies·g^-1, while its abundance in Wuyi State-owned Forest Farm, Zhangping City, Longyan City was the lowest, at 3.94×10⁸ copies·g^-1. The average abundance of FnirK gene in the nine plantations was 11.9×10₈ copies·g^-1. Random forest analysis indicated that soil pH was the most important environmental factor affecting FnirK gene abundance, explaining 21.02% of the total variations. FnirK gene abundance was significantly positively correlated with soil pH and mean annual precipitation (MAP), and significantly negatively correlated with soil dissolved organic carbon (DOC) and total carbon (TC). In conclusion, there is significant spatial heterogeneity in the abundance of denitrifying fungal functional gene FnirK in the soils of Chinese fir plantations in Fujian Province, with soil pH, DOC content, and MAP being the main factors influencing its distribution.

Key words: fungal denitrification, FnirK gene, subtropical forest, nitrous oxide