<p>Soil fertility and forest structure influence tree carbon stocks. However, it remains unclear how tree mycorrhizal types affect these relationships. This study addressed the question of how aboveground and belowground tree carbon stocks in soils with different mycorrhizal types are affected by soil fertility and forest structure. Tree demographic data were used from a 21.12-ha study area collected over a ten-year period (2009–2019), covering 43 species of woody plants and more than 50,000 individuals. Relationships between tree carbon stock, soil fertility and forest structure (stand density, diameter variation, species diversity and spatial distribution) were examined, as well as whether these relationships differed between arbuscular mycorrhiza and ectomycorrhizal mycorrhiza groups in a typical temperate conifer and broad-leaved mixed forest. We found that total tree carbon stock was positively impacted by variations in stand density and tree diameter but negatively influenced by soil fertility, tree species diversity and uniform angle index. Soil fertility promoted carbon stock of trees associated with arbuscular mycorrhiza (AM) but inhibited the carbon stock of trees with ectomycorrhizal mycorrhiza fungi (EcM). Carbon stock of AM trees was mainly influenced by soil fertility, while carbon stock of EcM trees was influenced by stand density. Our findings show that mycorrhizae types mediate the impact of stand structure and soil fertility on tree carbon stocks and provides new evidence on how forest tree carbon stocks may be enhanced based on the types of mycorrhizal associations. Tree species with different mycorrhizal types can be managed in different ways.</p>