Supplementary filling seedlings in secondary Pinus massoniana forests changed the structure of soil bacterial communities

Forest reformation can improve productivity and ecological service functions of forest resources. Nonetheless, the influence of different ways of forest reformation on soil microbial communities is still a complex and controversial issue. In this study, we investigated the effects of supplementary seedling planting (hereafter referred to as "filling seedlings") in secondary Pinus massoniana forests on soil bacterial community. We collected soil samples from original secondary P. massoniana forest and the forests filled with P. massoniana seedlings for 2, 4, and 6 years, respectively. We found that filling seedlings in the secondary P. massoniana forests changed the bacterial community structure compared to the original secondary forests. Filling seedlings in secondary P. massoniana forest significantly decreased soil bacterial abundance from 2.12 × 10⁷ copies g^-1 soil to 8.91 × 10⁶ copies g^-1 soil (n = 3) after six years of reformation, a decrease by 58.0%. Acidobacteriota (34.96% averagely) was the dominant phylum and Xiphinematobacteraceae (5.76% averagely) was the dominant family in all P. massoniana forests in this study. Soil parameters such as soil pH, soil organic matter, NH₄⁺, NO₃^-, and total and soluble P were significantly correlated with the structure of bacterial communities (p < 0.05). Moreover, the bacterial community structure and diversity changed over time during forest recovery. Our study demonstrated that filling seedlings in secondary P. massoniana forests could change soil bacterial community, which might in turn affect the nutrient cycling. This study provides scientific basis for managing low quality P. massoniana forests.