Responses of rhizosphere fungi to elevational gradients: distinct diversity and specialization of mycorrhizal and plant-pathogenic fungi in subalpine forests

Abstract Rhizosphere microbes are closely associated with forest community diversity and ecosystem functioning. Yet, how different rhizosphere fungal guilds and their interactions with host trees respond to environmental change remains poorly understood. To address this gap, we collected rhizosphere soil from 429 plant individuals representing 49 species across a 1200-m elevational gradient on Yulong Mountain in the subalpine forests of the Hengduan Mountains. By integrating host phylogeny, root traits, environmental and spatial variables, we quantified elevational patterns and drivers of putative mycorrhizal fungi (MF) and plant-pathogenic fungi (PF) diversity and composition, and compared their network structure and host specificity along the gradient. MF and PF showed distinct elevational responses at the individual, species and plot levels. MF richness peaked at mid-elevations and was mainly associated with soil temperature, and MF community composition was associated with soil C:N ratio. In contrast, PF richness declined with elevation and was mainly associated with spatial variables derived from geographic distances among plots, whereas PF community composition was associated with host root traits, especially root diameter. Network analyses further showed that specialization and host specificity in plant-MF associations displayed unimodal patterns along elevations, whereas both metrics increased with elevation in plant-PF associations. Collectively, these findings show that MF and PF are structured by distinct ecological filters along elevational gradients, resulting in guild-dependent patterns of plant-fungal network specialization in subalpine forests and providing new insights into plant–microbe dynamics under global change.