The fungal collaboration gradient drives root trait distribution and ecosystem processes in a tropical montane forest

Plant roots have a large diversity of form and function, which is also related to their degree of mycorrhizal association. This is known as the fungal collaboration gradient, where thin roots acquire resources by themselves and thicker roots depend on mycorrhizas. In this study, we, for the first time implement the fungal collaboration gradient in a trait-based Dynamic Vegetation Model (DVM, LPJ-GUESS-NTD). We test if the DVM can predict root trait distributions, as well as the effects of arbuscular mycorrhizal fungi (AMF) exclusion on ecosystem processes along an elevation gradient in a tropical montane forest in southern Ecuador. The model reproduces the observed root traits specific root length (SRL) and AMF colonization along the elevation gradient, which ranges from high SRL and low AMF colonization at 1,000 m to low SRL and high AMF colonization at 3,000 m. When AMF-mediated nutrient uptake is deactivated, simulated root traits do not change significantly, and in addition site average biomass values are reduced by up to 80%. Accounting for AMF-related belowground traits also affects simulated community leaf traits. The model suggests that the collaboration gradient has a substantial influence on vegetation diversity and functioning in the study system. We thus advocate more explicit treatment of root traits and mycorrhizae in DVMs. The model scheme here is based on general trade-offs and could be implemented in other DVMs and be tested for other study regions.