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

Climate warming poses a threat to the functionality of global dryland
ecosystems, while 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
(+0.5－1.6°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 modeling (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.