Abstract: Aims Soil microorganisms play a key role in the dynamics of plant communities. However, it is still unclear how soil microorganisms affect the survival and growth traits of different mycorrhizal tree species, and whether these effects change with the succession process, especially in tropical forest ecosystems. Methods In this study, six typical tropical tree species seedlings (three arbuscular mycorrhizal and three ectomycorrhizal fungal tree species) were selected to explore the effects of different succession stages and soil sterilization conditions on their survival and growth traits. Important findings 1) Sterilization significantly increased the survival rate of arbuscular mycorrhizal seedlings in the soil at the early stage of succession, but reduced the survival rate of exophytic mycorrhizal seedlings in the soil at the late stage of succession. The influence of soil microorganisms on the traits of seedlings is the combined effect of mycorrhizal type and succession stage: sterilization treatment significantly increased the specific leaf area and leaf length of arbuscular mycorrhizal seedlings in the soil at the early stage of succession, as well as the dry leaf weight and mycorrhizal infection rate of seedlings at the late stage of succession. Meanwhile, sterilization will reduce the leaf thickness and average root diameter of seedlings in the early stage of succession. In addition, sterilization treatment can significantly reduce the specific leaf area and average root diameter of exogenous mycorrhizal seedlings in the soil during the early stage of succession. Under unsterilized conditions, it promotes the increase of abovemground biomass, dry leaf weight, leaf length and root surface area of seedlings in the later stage of succession. 2) With the increase of the same density, the influence of soil microorganisms in the early stage of succession is stronger than that in the late stage of succession: in unsterilized soil, high density significantly promoted the growth traits of seedlings such as dry leaf weight, leaf length and leaf width. However, in sterilized soil, except for specific leaf area, most traits were inhibited. In addition, there are also significant differences in the survival and trait expression of seedlings of different species. These results suggest that root mycorrhizae may affect the performance of plants at different succession stages through interaction with soil microorganisms. Therefore, measures to promote the restoration of tropical forest vegetation using mycorrhizal fungi need to take into account mycorrhizal types, forest restoration stages, planting densities and even tree species, in order to minimize the adverse effects of soil microorganisms as much as possible.

Key words: tropical forest, soil microbes, functional traits, conspecific density, competition