Global patterns of mycorrhizal plant species richness across symbiotic types

ABSTRACT Mycorrhizal symbioses dominate terrestrial vegetation and play fundamental roles in maintaining ecosystem functions. The richness of plant species of a given mycorrhizal type has been proposed to underpin the resilience of ecosystem functions enabled by the respective type of mycorrhizal symbiosis. Yet, the global patterns of mycorrhizal plant species richness in natural ecosystems and the relative roles of climatic and edaphic drivers within and across arbuscular (AM), ectomycorrhizal (EcM) and ericoid mycorrhizal (ErM) plants remain poorly understood. In this research, we aimed to quantify global distribution patterns of AM, EcM, and ErM plant species richness at ecosystem level, and to assess the relative importance of climatic versus edaphic drivers. We estimated global patterns of mycorrhizal plant richness by combining global plant community data from the open sPlot database with genus-level mycorrhizal trait assignments from the FungalRoot database. Richness patterns were modelled using a generalized additive modelling (GAM) framework incorporating 19 climatic and 15 soil predictors. Prediction models were then used to generate global distribution maps of the three types of mycorrhizal plant species richness. Results showed that richness of AM plant species was primarily associated with broad-scale climatic gradients, particularly temperature-related gradients. In contrast, the richness of EcM and ErM plant species showed a stronger association with soil properties, especially soil C/N ratios. Global prediction maps highlighted strong spatial differentiation in the global distribution of AM, EcM, and ErM plant richness, with AM plant richness peaking in tropical regions, whereas the number of plant richness hotspots of EcM plants was highest in tundra, and temperate grasslands biomes, and the number of plant richness hotspots ErM plants peaked in temperate grasslands, and desert biomes. These findings provide a foundation for understanding the global biogeography of mycorrhizal plant species richness and their ecosystem responses to environmental changes.