Mycorrhizal type and soil pathogenic fungi mediate tree survival and density dependence in a temperate forest

Abstract

The Janzen-Connell hypothesis has been explored by many ecologists in a great number of forests. Numerous studies have suggested that mycorrhizal type and fungal composition may affect the conspecific negative density dependence (CNDD) among tree species. However, how the variations and roles of mycorrhizal type and fungi compositions influence CNDD remains a challenge in temperate forests. We used tree demographic data in a 42–ha plot over ten years to test the effects of two types of tree mycorrhiza (arbuscular mycorrhiza: AM and ectomycorrhizal mycorrhiza: EM) on the survival of 45 species over three types of tree ontogeny (sapling, juvenile, adult trees), and the relationship between CNDD and soil fungal community composition of 8 common species. The results of this study show that AM tree species experienced stronger CNDD than EM tree species in each of the three ontogenetic stages. EM tree species with higher mutualistic fungi and lower pathogenic fungi may suffer lower CNDD. Individual trees with higher pathogenic fungi may be affected more severely by CNDD in our temperate forest. Our findings highlight the key roles of mycorrhizal association in mediating the strength of CNDD on tree survival, which may affect the plant community composition of temperate forests.