Climate and Land-Use Changes Predicted to Jointly Drive Soil Fungal Diversity Losses in One-Third of North American Coniferous Forests.

Soil fungi underpin key ecosystem functions but face increasing threats from climate and land-use changes, with their future impacts remaining unclear. This uncertainty is exacerbated by limited large-scale data and the challenge of quantifying and comparing both factors at comparable spatial scales. By leveraging two continental-scale sampling networks in North America and applying stacked species distribution models combined with countryside species-area relationship frameworks, we assessed the impacts of climate and land-use change on soil fungal diversity and identified regions affected by both factors across four biomes. We projected climate and land-use change by incorporating shared socioeconomic pathways (SSPs) and associated greenhouse gas-induced radiative forcing, focusing on moderate- (SSP2-4.5) and high-emission (SSP5-8.5) scenarios. Climate change typically led to both diversity losses and gains, particularly in coniferous forests and among arbuscular mycorrhizal (AM) fungi. Land-use change predominantly caused diversity losses under SSP2-4.5, especially in broadleaf-mixed forests and for ectomycorrhizal (EM) fungi, with these effects diminished under SSP5-8.5 due to minimal land-use changes. Across emission scenarios, both factors were predicted to cause widespread diversity losses in coniferous forests (whole-community, EM fungi, and soil saprotrophs) and grasslands (AM fungi and plant pathogens) while promoting gains in broadleaf-mixed forests (whole-community, EM fungi, and saprotrophs) and coniferous forests (AM fungi and pathogens). These results support the need for biome- and guild-specific fungal conservation planning under global change.