Objective The aims were to investigate the differences and variations in soil nutrients and enzyme activities in different Pinus massoniana forest types in Dabie Mountains of North Subtropical region and to explore the main factors influencing soil nutrient cycling and enzyme activities in growing seasons.

Method This study focused on pure Pinus massoniana forest, Pinus massoniana-Liquidambar formosana mixed forest, Pinus massoniana-Platycarya strobilacea mixed forest, and Pinus massoniana-Quercus acutissima mixed forest. Soil pH, fertility-related indicators, and the activities of soil cellulase (S-CL), sucrase (S-SC), acid protease (S-ACPT), urease (S-UE), and acid phosphatase (S-ACP) in July and September were measured. The correlations between soil enzyme activities, stoichiometric ratio, and soil pH and fertility-related indicators were analyzed.

Result ① The soil total nitrogen and organic carbon content of Pinus massoniana-Quercus acutissima mixed forest were significantly higher than those of the other three forest types in July and September. The soil nitrate nitrogen content of Pinus massoniana-Platycarya strobilacea mixed forest was the highest among the four forest types during different growing seasons. ② In July and September, the soil S-SC and S-ACPT activities of Pinus massoniana-Quercus acutissima mixed forest were significantly higher than those of the other three forest types. The soil enzyme activities in the same Pinus massoniana forest type during different growing seasons showed that the S-CL activity of the four forest types was higher in July than in September. The enzyme C∶P ratio, enzyme N∶P ratio of Pinus massoniana-Platycarya strobilacea mixed forest were higher than those of the other three forest types. ③The correlation analysis showed that in July, soil S-CL and S-UE activities were significantly positively correlated with soil pH, total nitrogen, total phosphorus, and organic carbon content. Soil S-SC, S-ACPT activities, and enzyme vector length were significantly positively correlated with soil ammonium nitrogen content. In September, soil S-CL, S-UE, S-ACPT, and S-ACP activities were significantly positively correlated with soil total nitrogen, total phosphorus, and organic carbon content. The enzyme C∶P ratio, N∶P ratio, and enzyme vector length were significantly negatively correlated with soil C∶N and C∶P ratio. ④ Redundancy analysis indicated that soil total phosphorus, organic carbon, and nitrate nitrogen content significantly contributed to soil enzyme activity and stoichiometric ratio, and were the main factors affecting soil enzyme activity and stoichiometric ratio.

Conclusion Among the four Pinus massoniana forest types, Pinus massoniana-Liquidambar formosana mixed forest and Pinus massoniana-Quercus acutissima mixed forest effectively improved soil nutrient levels and enzyme activity, promoting soil nutrient cycling in mixed forests.