Warming modulates soil multifunctionality through assembly processes and co‐occurrence patterns of arbuscular mycorrhizal fungal communities in drylands

Abstract Climate warming poses a threat to the functionality of global dryland ecosystems, where arbuscular mycorrhizal fungal (AMF) communities play a critical role in maintaining ecosystem stability and functioning. However, it remains unclear how the assembly mechanisms and co‐occurrence network patterns of AMF communities respond to warming and regulate soil multifunctionality. We conducted a three‐year warming experiment (ranging from +0.5°C to +1.6°C) using open‐top chambers (OTCs) in the Tengger Desert to investigate the assembly processes and co‐occurrence network patterns of AMF in the rhizosphere soil of dominant shrubs, Artemisia ordosica and Caragana korshinskii. By measuring 15 soil functional indicators (including nutrient availability, biogeochemical cycles, microbial activity and microbial productivity), we constructed a soil multifunctionality index and employed structural equation modelling (SEM) to uncover the mechanisms by which AMF communities regulate soil multifunctionality. Our results showed that warming increased the network complexity of AMF communities associated with C. korshinskii by 8%–145%, while decreasing that of the A. ordosica by 14%–80%. Stochastic processes dominated the assembly of AMF communities, with warming reducing the stochasticity of AMF communities in C. korshinskii while increasing it in A. ordosica . Notably, the two species showed distinct functional response pathways: For A. ordosica , warming‐induced reduction in soil water content suppressed the mycorrhizal colonization rate (36%–79%) through a ‘stochastic assembly‐network collapse’ cascade effect, subsequently leading to decreased soil multifunctionality (54%–172%). In contrast, for C. korshinskii , the soil water reduction caused by warming maintained higher colonization rates (82%–198%) by enhancing AMF network complexity, thereby improving soil multifunctionality (43%–228%). We further proposed a conceptual framework that integrates niche theory into a mechanistic understanding of how stochastic processes and network complexity of AMF communities affect soil multifunctionality under climate warming. Overall, our study suggests that warming modulates soil multifunctionality by affecting the assembly processes and network complexity of AMF communities, exhibiting species‐specific responses. This provides crucial theoretical support for understanding the mechanisms underlying functional evolution in drylands and for formulating climate adaptation strategies. Read the free Plain Language Summary for this article on the Journal blog.