Extreme drought disrupts the bottom-up regulation of ground-dwelling invertebrate diversity under climate warming

Extreme climate events are becoming more frequent, yet their consequences for the recovery of plant-invertebrate relationships under warming remain poorly understood. We investigated over two years of how ground-dwelling invertebrate communities recovered from a 40-days drought in outdoor grassland mesocosms exposed to ambient conditions, constant warming or periodic heatwaves, and both combined. We then examined how post-drought community shifts were associated with above-ground plant biomass, measured concurrently with invertebrate sampling. Drought had no detectable effect on total invertebrate abundance at either recovery time (one or four months after drought). By contrast, diversity showed warming-dependent responses one month after drought and a delayed drought legacy four months later, when diversity declined only under constant warming, with or without periodic heatwaves. At the four-month post-drought sampling, plant biomass-invertebrate diversity coupling was evident only in non-drought plots, with negative relationships under ambient and heatwave regimes but a positive relationship under constant warming alone. This pattern was largely associated with responses of herbivores, particularly Stylommatophora. Our results highlight lagged drought effects in invertebrate diversity that emerged months later and, under warming, extended to weakened plant biomass-invertebrate diversity coupling, pointing to disrupted bottom-up control with potential consequences for food-web functioning.