Microbial communities in semi-mature oak trees are resilient to drought, nutrient limitation, and pathogen challenge

Global forest biomes face increasing stressors and disease outbreaks that threaten ecosystem health. Tree-associated microbiota are vital for tree resilience, yet their responses to biotic and abiotic stressors in mature trees remain poorly understood. Using an experimental woodland plot of 144 Quercus petraea trees subjected to drought (rain exclusion), nutrient stress (ringbarking), and biotic treatments (bacterial pathogens and beetle larvae) to simulate acute oak decline, we tracked microbial communities in leaf, stem, and root/rhizosphere tissues across four time points over 2 years. Oak trees hosted distinct microbial communities across tissue types, which remained largely stable under stress. Rain exclusion significantly altered microbiota composition, though these changes explained less than 1% of total variance. Actinobacteriota, linked to drought tolerance, increased in the root/rhizosphere of rain-excluded trees. These findings reveal a surprising resilience of oak-associated microbial communities to environmental and biotic disturbances, highlighting their potential role in forest ecosystem stability.