Fungal-bacterial interaction unaffected by heatwave conditions

Climate change is reshaping soil microbial communities, yet the impact of warming in bacterial-fungal interactions (BFIs) remains underexplored. We investigated whether heatwave temperature influence BFIs and the mechanism supporting the interaction. Using co-culture experiments with two bacterial and two fungal strains isolated from heathland soil, we compared mono- and co-cultures final abundances under ambient (18{degrees}C) and heatwave (25{degrees}C) soil temperatures. Our results revealed strongly asymmetric interactions, where fungi benefited by around 5% from bacterial presence, while bacterial abundance was inhibited by around 68%, regardless of temperature. Analyses of pH confirmed that acidification by fungi was probably the main cause of this inhibition. Moreover, warming did not affect the strength or direction of these interactions, though it slightly increased fungal abundance. These findings provide direct experimental evidence that fungi can impact bacteria via acidification, and that the interaction is unaffected by temperature. Understanding these mechanisms is crucial for improving predictions of microbial community dynamics and ecosystem functioning in warming environments.