Abstract: [Objective] This paper investigated the variation of soil nutrients and oligotrophic bacterium, Acidobacterium communities during continuous planting of Cunninghamia lanceolata plantation in Kaihua, Zhejiang Province, to reveal the molecular ecological mechanism of Acidobacterium causing soil fertility changes in different types of C. lanceolata plantations. This study aimed to provide scientific basis for the adjustment of C. lanceolata stand structure, the scientific management of soil resources as well as the construction of healthy soil ecosystem in this area.[Method] The soil samples at different depths (0-20 cm, 20-40 cm) were collected from three different plantations:Pinus massoniana plantation(served as control);the first rotation of C. lanceolata plantation established after the clear cutting of P. massoniana, and the natural regeneration second rotation of C. lanceolata plantation, in Kaihua Forestry Farm in Zhejiang. Nutrient contents, physical and chemical properties of soil were analyzed. Then, the bacterial 16S rDNA in soil was analyzed using high-throughput sequencing.[Result] 1) The replacement of P. massoniana plantation with C. lanceolata plantation led to a significant decrease in pH value, alkali-hydrolyzable nitrogen, available phosphorus and available kalium content(P<0.05). The soil fertility was ranked as the order of P. massoniana plantation > the first-rotation C. lanceolata plantation > the second-rotation C. lanceolata plantation. 2) On the phyla level, Acidobacteria were dominant in soil bacteria of the three forest types, accounting for 32.68%-49.17%. The Acidobacteria proportion in 0-20 cm soil layer of the second-rotation C. lanceolata plantation was significantly higher than that of P. massoniana plantation (P<0.05). 3) A total of 18 groups of Acidobacteria were detected and classified, among which Gp2 was the dominant group representing 47.74%-68.07% of the Acidobacteria. Gp1 occupied the second ranking, accounting for 18.35%-29.72%, followed by Gp3, accounting for 13.30%-22.41%. The dominance of Gp2 in Acidobacteria group was strengthened, and Gp3 had the trend of changing from dominant bacteria to subdominant bacteria. The relative dominance of Gp1 was significantly negatively correlated with soil pH(P=0.035), and that of Gp2 had a significantly negative correlation with available P(P=0.010), while Gp10 had a significantly positive correlation with soil pH(P=0.035).[Conclusion] With the increasing rotation of plantation, the soil available nutrient level was decreased, while the proportion of Acidobacteria was increased. The dominant genera within Acidobacteria varied with the soil environment, suggesting that Acidobacteria played important roles in soil nutrient cycling in C. lanceolata plantation.

Key words: Cunninghamia lanceolata plantation, soil fertility, 16S rDNA sequencing, soil Acidobacteria, community structure