Objective Exploring the effects of forest age growth on soil bacterial communities in Eucalyptus sp. plantation can provide a theoretical basis for improving soil ecosystem function of eucalyptus plantation.

Method Soil physical and chemical properties, microbial biomass, and soil bacterial community composition, co-occurrence network, functional characteristics, and their influencing factors were analyzed in eucalyptus plantation of different ages (1-year-old, 2-year-old, 3-year-old, 5-year-old, and 7-year-old) in the State-Owned Daguishan Forest Farm of Guangxi, southern China as the research object.

Result (1) With the growth of stand age, soil total organic carbon (TOC), total nitrogen (TN), dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and microbial biomass carbon (MBC) as a whole showed a decreasing and then increasing trend, and microbial biomass nitrogen (MBN) and phosphorus (MBP) increased significantly with the growth of stand age. (2) The soil nutrient stoichiometric ratios of TOC/TN showed an increasing and then decreasing trend, while MBN/TN and MBP/TP increased significantly with the age of forest, and MBC/MBN and MBC/MBP decreased significantly with stand age, which was characterized by “surface layer aggregation”, and TOC/TP, TN/TP, MBC/TOC and MBN/MBP showed different patterns and were greatly influenced by soil layer. TOC/TP, TN/TP, MBC/TOC, and MBN/MBP showed different patterns and were greatly influenced by soil layer. (3) α-diversity decreased significantly with increasing soil depth and dominant soil bacterial taxa were Acidobacteria and Proteobacteria phylum. (4) Co-occurrence network analysis showed that bacteria were dominated by co-occurrence, with greater synergistic effects among bacteria, and the network complexity was higher in 7-year-old stand, suggesting that its more complex interactions among bacterial communities were conducive to stabilization of soil biological factors. Bacterial functions were predicted to be dominated by carbohydrate metabolism and amino acid metabolism, and most of unctional differences were not significant with stand age. (5) TN, DON, TP, and TN/TP were significantly and positively correlated with lower abundance bacterial groups WPS-2 phylum, Bacteroidetes phylum, and Firmicutes phylum, suggesting that lower taxa may also play a role in maintaining soil stability.

Conclusion It is initially shown that C, N and P in the soil of eucalyptus plantation are important limiting factors in growth process, and attention should be paid to the growth management of eucalyptus plantation in the early stage, appropriately lengthening the rotational period, and applying organic fertilizers or bacterial fertilizers to improve the stability of structure of bacterial community, especially the stability of dominant taxa, which is of great significance to the improvement of quality of eucalyptus plantation soils and sustainable development of eucalyptus plantation.