Plant Growth Form Shapes the Global Biogeography of Mycorrhizal Symbioses

ABSTRACT Aim Most seed plants are associated with one of four major types of mycorrhizal fungi: arbuscular (AM), ectomycorrhizal (ECM), ericoid (ERM) or orchid (ORM) fungi. These mycorrhizal types have evolved in close association with plant growth form (i.e., woody vs. herbaceous species). However, it remains unclear how the biogeography of mycorrhizal plants varies across different growth forms. Location Global. Time Period Current. Major Taxa Studied Seed plants. Methods By integrating newly compiled databases of species distributions, mycorrhizal types and growth forms for over 300,000 seed plant species, we demonstrated how the geographic patterns of mycorrhizal plant species and their drivers vary between woody and herbaceous species. Results We found that the geographic patterns of mycorrhizal plants were more strongly associated with latitude and environmental variables when woody and herbaceous species were analysed separately, compared to when all species were analysed together. Specifically, in woody species, the proportion of AM species decreased towards high latitudes, while the proportion of ECM and ERM species increased. In herbaceous species, the proportion of AM species increased towards high latitudes, while the proportion of ORM species decreased. These geographic patterns of different mycorrhizal plants were primarily driven by temperature in woody species but by precipitation in herbaceous species. Interestingly, soil properties played significant roles in shaping the geographic patterns of mycorrhizal plants in both growth forms. These results suggest that mycorrhizal associations play different roles in mediating woody and herbaceous plant adaptation to environmental conditions. Main Conclusions Our study provides the global patterns in the proportions of different mycorrhizal types and demonstrates that the drivers underlying these patterns depend on plant growth forms. We suggest that mycorrhizal symbiosis related to plant growth forms may play an important role in shaping global plant diversity patterns.