Objective This article aims to analyze the changes of soil available nitrogen content in Chinese fir plantations at different generations, and explore the internal relationship between nitrate nitrogen and the structure and diversity of ammonia-oxidizing archaea community, which provides reference for the effective use of soil nitrogen of plantations and soil quality assessment of Chinese fir forest.

Method Four Chinese fir plantations with different generations were selected in Nanping, Fujian Province. High-throughput sequencing technology was used to determine the amoA gene amplified by PCR. Mantel_r correlation analysis, random forest model and partial least squares path model were used to study the relationship between soil available nitrogen content, ammonia-oxidizing archaea community abundance and diversity in different generations.

Result With the increase of continuous cropping generations of Chinese fir, the content of nitrate nitrogen (NO₃⁻-N) decreased significantly, and the content of ammonium nitrogen (NH₄⁺-N) and microbial biomass nitrogen (MBN) did not change significantly. Soil enzyme activity and the abundance and diversity of ammonia-oxidizing archaea (AOA) community showed a decreasing trend. Soil available nitrogen content was closely related to ammonia-oxidizing archaea community and enzyme activity, and the abundance and diversity of ammonia oxidizing archaea community was the most important factor affecting nitrate nitrogen content.

Conclusion With the increase of planting generation, the abundance and diversity of ammonia oxidizing archaea community decrease to a certain extent. Except for the fourth generation of soil urease and ammonia nitrogen oxygenase enzyme activity increased slightly, soil nitrogen cycle related enzyme activity shows a decreasing trend, resulting in a significant reduction in soil nitrate nitrogen content, which limits the effectiveness of soil nitrogen in continuous cropping Chinese fir plantations.