Ecological Determinants of Soil Fungal Communities Along a Successional Gradient in Upper Andean Tropical Forests and Their Influence on Decomposition

Soil fungi are vital in regulating ecosystem functions, yet changes in their communities during tropical montane forest succession and their roles in litter decomposition remain underexplored. This study investigates the main drivers of soil fungal communities along a successional gradient in upper Andean tropical forests and their influence on decomposition. Soil fungi were sampled from the topsoil in 14 permanent plots across four forest sampling sites in the Andean mountains surrounding Bogotá, Colombia. We collected data on microclimate, soil nutrients, plant diversity, forest biomass, litter functional richness, and decomposition rates from these plots. Using Illumina sequencing to amplify the ITS1 region, we analyzed data with OTUs as a proxy for species richness and calculated Hill numbers to assess fungal diversity. ANOSIM and NMDS indicated significant differences in fungal communities between forest sampling sites. Reduced major axis regressions showed no changes in fungal diversity along the successional gradient, using aboveground biomass as a proxy of successional status. However, fungal diversity varied with minimum soil surface temperature, litter functional richness, plant diversity, and soil calcium. Fungal diversity was not related to decomposition rates, as relationships between fungal guilds and decay rates of each litter species neutralized this effect. Plant pathogen diversity appeared to negatively influence decomposition, likely due to metabolic responses in plants that slow down the process. Our findings reveal that each Andean forest site hosts distinct fungal communities and that anthropogenic changes in drivers like soil nutrients, plant diversity, and microclimate may affect their diversity and role in decomposition.