Longer heatwaves disrupt bacterial communities by decoupling resistance from recovery

Ana-Hermina Ghenu , Anjaney J Pandey, Zachary M Bailey, David R Johnson, Madhav P. Thakur

Periodic heatwaves are increasing in duration, yet their ecological impacts on communities remain poorly understood. We experimentally tested how synthetic communities of soil Pseudomonas species respond to heatwaves of increasing duration. We used a resistance-recovery framework and growth rate-heat tolerance trade-offs to predict whether prolonged stress erodes community stability. Communities composed of species with different growth rates were exposed to single heat pulses lasting 6, 12, 24, or 48 hours. Although we expected the fastest-growing and most heat-tolerant species, P. putida, to dominate, a species with moderate growth and heat tolerance, P. protegens, consistently prevailed. This outcome was likely driven by diffusible toxins and unexpectedly high heat tolerance linked to density-dependent growth. On average, each additional hour of heat exposure increased community extinction risk by 21.5%, with faster-growing communities exhibiting lower risks. The longest heat pulse caused sharp declines in diversity and productivity, leading to greater decoupling between resistance and recovery as well as reduced overall stability. These findings demonstrate that growth rate and species interactions — not heat resistance alone — determine community fate during and after heat stress. Our results highlight the need to incorporate nonlinear dynamics and trait-based interactions when predicting microbial responses to climate extremes.