Tree Growth Response to Neighborhood Density Differs Among Mycorrhizal Types Across Life-History Stages in a Warm Temperate Forest

The mechanisms controlling plant growth are important to understand as they are key to forest carbon sequestration. Growth is species-specific and depends on mycorrhizal associations, resource availability, and neighbor competition. However, the difference in conspecific negative density dependence (CNDD) on growth between arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) species across life stages needs exploration. Using data from a 20 ha warm temperate deciduous broad-leaved forest in Donglingshan, China, we measured growth of established individuals. Using linear mixed-effects models, we assessed the combined effects of neighbor density, soil factors, and light availability on growth across life stages and mycorrhizal types. We observed reduced growth with increasing conspecific density, but effects varied between AM and EM species and between saplings and trees. Conspecific neighbor density had stronger negative effects on AM than EM saplings. For mature trees, conspecific density had weaker negative effects on AM species and no significant effect on EM species. Additionally, soil factors promoted AM sapling growth, while light promoted EM sapling growth. For trees, light promoted growth in both AM and EM species, whereas soil factors inhibited EM tree growth. Conspecific crowding, light and soil act jointly on growth, with CNDD strength set by mycorrhizal type and life stage.