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.