Abstract: Mixed forests play an important role in improving protective efficiency and stability of forest stands by establishing multilayer or thick-canopy structures. In this study, a 20-year-old masson pine (Pinus massoniana) plantation was harvested with 5 different cutting intensities (clear-cutting, heavy, moderate, light and very light grades), resulting in the canopy closure of 0, 0.4, 0.5, 0.6 and 0.7 respectively. Then cinnamon (Cinnamomum cassia) was planted equally to the quantity of removed masson pine. After the treatments for seven years, the BIOLOGECO method was applied to analyze the soil microbial functional diversity. The results showed that the soil physicochemical properties, AWCD (average well color development) and microbial community functional diversity index in mixed forests were superior to both the masson pine and cinnamon pure stands. The values of abovementioned properties were the lowest in the cinnamon pure stands, while the mixed stands developed from the treatment of light cutting intensity (with a canopy closure of 0.6) had the highest values, being significantly different from those of the masson pine pure stands. The functional diversity of soil microbial communities decreased with the increase of soil depth. Principal component analysis showed that the utilization characteristics of soil microbial carbon sources were not significant among different mixed patterns but obviously different among different forest types, mainly contributed by amino acids, carboxylic acids and sugars. The differences of soil microbial carbon source utilization in different stands were significantly affected by soil water content and organic matter content. Also, other factors such as soil water content, organic matter content, total nitrogen content, total phosphorus content, total potassium content and the ratio of carbon to nitrogen had important impacts on soil microbial community functional diversity. In conclusion, the microbial activity and functional diversity of soil were improved by introducing cinnamon to grow in the masson pine stands, which would offer a reference for transforming masson pines pure forest into mixed forests.

Key words: vegetative filter strip, N intercepting rate, hydraulic characteristic, inflow conditions, P intercepting rate