ITS amplicon sequencing of root-samples across a Western Himalayan precipitation gradient (Ladakh and Himachal Pradesh, India), 2015 and 2022
Microbial community responses to environmental gradients are often analysed at the community level, but pooled metrics can mask divergent responses among co-occurring functional guilds that track the same gradient through different ecological pathways. We tested how aridity reorganises root-associated fungi at three nested scales — among guilds, within surviving genera, and across co-occurring hosts — using repeated sampling of dominant alpine plant species along a Western Himalayan precipitation gradient (>1290 to <210 mm per year) in 2015 and 2022. Guild-specific structural equation models, redundancy analysis, and hierarchical joint species distribution modelling resolved precipitation-linked variation differently across guilds: saprotroph composition showed the strongest signal along the coupled climate-soil gradient; plant-pathogen composition showed a positive total precipitation association, but its soil-associated component remained unresolved; and root-symbiont composition tracked precipitation independently of bulk-soil properties. Root-symbiont relative richness declined toward the arid extreme while pathogen richness increased. Arid-extreme operational-taxonomic-unit pools were predominantly nested within wetter-site pools rather than representing novel extremophile assemblages. Within root symbionts, endophytes showed greater cross-host heterogeneity than mycorrhizal fungi, even though the large-scale gradient remained stable across years. A pooled-community structural equation model mirrored the saprotroph pattern, masking the soil-independent root-symbiont signal. Together, these results show that environmental filtering operates on microbial communities through guild-specific pathways, that pooled metrics can systematically obscure the strongest underlying signals, and that scale-dependent assembly patterns emerge only when functional structure is preserved.
Microbial community responses to environmental gradients are often analysed at the community level, but pooled metrics can mask divergent responses among co-occurring functional guilds that track the same gradient through different ecological pathways. We tested how aridity reorganises root-associated fungi at three nested scales — among guilds, within surviving genera, and across co-occurring hosts — using repeated sampling of dominant alpine plant species along a Western Himalayan precipitation gradient (>1290 to <210 mm per year) in 2015 and 2022. Guild-specific structural equation models, redundancy analysis, and hierarchical joint species distribution modelling resolved precipitation-linked variation differently across guilds: saprotroph composition showed the strongest signal along the coupled climate-soil gradient; plant-pathogen composition showed a positive total precipitation association, but its soil-associated component remained unresolved; and root-symbiont composition tracked precipitation independently of bulk-soil properties. Root-symbiont relative richness declined toward the arid extreme while pathogen richness increased. Arid-extreme operational-taxonomic-unit pools were predominantly nested within wetter-site pools rather than representing novel extremophile assemblages. Within root symbionts, endophytes showed greater cross-host heterogeneity than mycorrhizal fungi, even though the large-scale gradient remained stable across years. A pooled-community structural equation model mirrored the saprotroph pattern, masking the soil-independent root-symbiont signal. Together, these results show that environmental filtering operates on microbial communities through guild-specific pathways, that pooled metrics can systematically obscure the strongest underlying signals, and that scale-dependent assembly patterns emerge only when functional structure is preserved.
University of South Bohemia, Faculty of Science