Objective  Under the background of carbon neutrality, the carbon fixation capacity of forests has become the focus of attention. Previous studies have shown that tree diversity can increase biomass and carbon storage, and the main research focuses on the living body and soil of the forest. However, the impact mechanism of tree diversity on the biomass and carbon storage of standing dead branches is still unclear.

  Method  Based on the experimental research platform of subtropical forest biodiversity and ecosystem function in China (BEF China), this study aimed to explore the impact of tree species diversity on the carbon storage of standing dead branches by measuring the tree height, DBH and carbon storage of 12 tree species from different types under different diversity levels (1, 2, 4, 8).

  Result  Tree species types significantly affected the basal area, tree height and carbon storage of dead branches of different arbuscular mycorrhizal species (P < 0.01), and also significantly affected the NE (net effect), CE (compensation effect) and SE (selection effect) of carbon storage of dead branches (P < 0.05); Generally speaking, the fixed effects (plot diversity, basal area and tree height) and random effects (tree species) of arbuscular mycorrhizal and positive tree species explained more variation of carbon storage of dead branches and biodiversity effects (the average value was about 40%, and the minimum value was more than 32%); moreover, the net effect and compensation effect of dead branch carbon storage from arbuscular mycorrhizal species and positive species decreased with the increase of sample plot diversity (P < 0.05), while the ectomycorrhizal species and negative species were not affected by sample plot diversity.

  Conclusion  From the perspective of carbon sink of dead branches, the selection of different mycorrhizal types and shade tolerant tree species can significantly affect the carbon storage of standing dead branches. Meanwhile, planting more monoculture from arbuscular mycorrhizal species and intolerant species is beneficial to the formation of carbon sink of dead branches in subtropical forests.