ObjectiveExploring the variations of soil nutrients and bacterial communities in Larix principis-rupprechtii plantations with different generations is helpful to understand maintenance mechanisms of soil fertility. It provides a reference for the sustainable management of Larix principis-rupprechtii plantation.

MethodIn this study, three Larix principis-rupprechtii plantations with different generations, including 17 years old first generation (Y1R), 37 years old first generation (M1R), 14 years old second generation (Y2R), were selected in Saihanba Area of northern China. The coupling relationship between soil nutrients and bacterial communities and their changes over generations were analyzed.

Result(1) In depths of 0−10 cm and 10−20 cm, the contents of soil readily available potassium (AK) and available phosphorous (AP) were significantly higher in Y1R and Y2R than in M1R (P < 0.05). There were no significant differences in soil AK and AP between Y1R and Y2R (P > 0.05). Soil nutrients showed a decreasing trend with increasing soil depths in all generations. (2) The dominant bacterial phyla were Proteobacteria, Actinobacteria, Verrucomicrobia and Acidobacteria in all generations. Proteobacteria and Actinobacteria decreased with increasing soil depth in all generations. (3) The ACE and Chao1 indicators of bacterial community were the lowest in M1R and their changes were significant among generations at depths of 0−10 cm and 10−20 cm. In all three soil layers, the soil bacterial diversity indicators were relatively higher in Y1R and Y2R than in M1R. (4) Correlation analysis showed that AK had significantly positive effects on Proteobacteria and Actinobacteria, while had significantly negative impact on Nitrospirae (P < 0.05). The number of Proteobacteria increased significantly with increasing AP content (P < 0.05).

ConclusionSoil fertility doesn^,t decline at the early development stage in second generation of Larix principis-rupprechtii plantations. Strengthening the regulation of soil available potassium, alkali hydrolyzable nitrogen and available phosphorus, and focusing on changes in specific soil microorganisms could be the optimum alternatives to improve soil fertility.