Bacterial communities living in the soil can affect forests natural regeneration, but the effects of their composition and network inference on regeneration of Larix principis-rupprechtii Mayr plantations remain largely elusive. Therefore, the redundancy analysis and structure equations modeling of affecting elements for the regeneration of L. principis-rupprechtii plots including the diversity, composition and network structure of soil bacteria, topographic factors, light factors, and soil physicochemical properties have been conducted. It was found that the increased modularity of the soil bacterial community co-occurrence network and the enrichment of metabolic pathway bacteria had a significant positive effect on the successful regeneration (total effect of 0.84). The complexity of the soil bacterial community gradually decreased with the increase of stand regeneration, and the composition and structure of the flora became simpler (with standard path coefficients: −0.70). In addition, altitude also had a positive effect on regeneration with a total effect of 0.39. Soil nutrients had significantly negative effects on regeneration with total effects of −0.87. Soil bacterial communities may mediate the effects of soil nutrients, altitude, litter thickness, and herbaceous diversity on regeneration in L. principis-rupprechtii plantations. The results provide a great contribution to our understanding of regeneration-soil bacterial community interactions and the basis and important data for sustainable management of L. principis-rupprechtii plantations in the Lvliang Mountains located in northern China.

Forest gaps create a favorable microenvironment for the growth of the soil microbial community. This study aimed to explore the effects of gap-related microenvironmental heterogeneity on soil bacterial communities in Larix principis-rupprechtii Mayr forest gaps. Therefore, the redundancy analysis (RDA) and structure equations modeling (SEM) of affecting elements were further used to test the significance of forest gaps’ effect on soil bacterial community composition and co-occurrence structure complexity. The formation of forest gaps increased canopy opening (CO) and significantly increased soil moisture content (SW), soil temperature (ST) and the accumulation of acid phosphatase (PHO) and sucrase (INV) in the soil, and the G250 (forest gap size: >250 m2) was most conductive to the accumulation of light and soil total nutrient. G50, G70, and G100 (forest gap size: 50–70 m2, 70–100 m2, 100–125 m2) were most favorable for the natural regeneration of the L. principis-rupprechtii Mayr plantation. The light properties under the forest gaps were the most significant factor that influenced the soil bacterial community composition, followed by the size of the forest gap, with standard path coefficients (Std. PCs) of 0.45 and −0.37, respectively. The canopy opening (CO), relative light intensity (RLA) and leaf area index (LAI) were considered to be the most important environmental factors affecting bacterial community composition (Std. PCs: 0.97, 0.99, and −0.93, respectively). The natural regeneration density under the forest gap was the most significant factor influencing the complexity of the soil bacterial community co-occurrence network, followed by soil nutrients (Std. PCs: 0.87 and −0.76, respectively).