Format: ORAL

Albert Vil-Cabrera1,2 Julen Astigarraga3 Kirsten OSullivan1 Josep Padulls-Cubino1 Karina Clemmensen4 Jan-Chang Chen5 Sarah Greenwwod2 Alistair Jump2

1 CREAF, Catalonia, Spain 2 Biological and Environmental Sciences, Faculty of Natural Sciences, University of Stirling, Stirling, UK 3 Forest Ecology and Restoration Group, University of Alcalá, Spain 4 Department of Forest Mycology and Plant Pathology, Swedish University of Agricultural Sciences, Uppsala, Sweden 5 Department of Forestry, National Pingtung University of Science and Technology, Pingtung, Taiwan

Symbiotic associations between trees and soil fungi mycorrhizas influence forest structure and diversity, with important differences between mycorrhizal types. It is thought that communities dominated by ectomycorrhizal associations exhibit weaker negative conspecific density dependence because of improved nutrient acquisition and protection against soil-borne pathogens to conspecifics, relative to arbuscular mycorrhizal associations. This mechanism should explain stand-level gradients of tree diversity, with low-diverse forest communities dominated by ectomycorrhizal trees and high-diverse communities dominated by arbuscular mycorrhizal trees. Here, we tested this hypothesis across tropical montane forests and found that, in general, tree species diversity was lower under the dominance of either ectomycorrhizal or arbuscular mycorrhizal trees, and higher in mixed communities of both mycorrhizal types. However, this pattern was dependent on forest stand development and climate, with ectomycorrhizal dominance differentially influencing tree diversity between young and old-growth forests, from cold to warm climates. In particular, ectomycorrhizal dominance was associated to increased tree species richness but decreased tree species evenness across old-growth forests located in median- and warm conditions along the climatic gradient. Our findings indicate that mycorrhizal associations may represent an important factor shaping forest biodiversity in subtropical and tropical regions, the most species-rich and varied environments of the planet but currently at risk from the pressures of human-driven environmental changes.