Abstract: Soil bacteria, by participating in the soil nutrient cycling process, directly or indirectly regulate tree regeneration and survival. We established a 1-ha plot in the mixed forest of Picea asperata and Larix principis-rupprechtii and conducted a location-based survey of the regeneration seedlings, combining with collecting soil samples from 75 sampling points. The results showed that (1) Regeneration seedlings (n = 275) showed a patchy distribution, with density decreasing across height classes and smaller seedlings aggregating over shorter distances. As the scale increasing, the distribution pattern tends to become random; (2) Soil bacteria and nutrients also exhibited spatial heterogeneity and primarily shaped by structural spatial factors (range: 8.4–17.1 m); (3) Bacterial effects on tree regeneration were indirect by mediating through changes in soil nutrient availability (pc = 0.28). Specifically, bacteria competed with seedlings for beneficial macronutrients (pc = 1.19*, –0.85*) but mitigated toxicity by absorbing harmful micronutrients (pc = –0.48*, –0.75*). These findings highlight the role of bacteria-mediated nutrient dynamics in shaping regeneration patterns in warm-temperate mixed forests.

Key words: Mixed forest, Tree regeneration, Soil bacteria, Soil nutrients