Repeated heat fluctuations amplify growth advantages of invasive over native plants​

Increasing climate variability is expected to impose stronger selective pressures on plant communities than gradual warming alone, yet how repeated heat stress and recovery cycles influence plant performance remains poorly understood. Here, we compared the dynamic growth responses of three invasive and three native Asteraceae species exposed to three consecutive cycles of high temperature (40°C) and ambient temperature (26°C) under controlled conditions. Using destructive sampling across seven time points, we quantified growth trajectories and biomass allocation patterns throughout the fluctuation process. Repeated heat fluctuations induced pronounced divergence in growth dynamics between invasive and native plants. Invasive species exhibited significantly accelerated biomass accumulation under fluctuating conditions compared with constant ambient conditions, whereas native species showed no corresponding increase in growth rate and instead experienced progressive growth suppression. Biomass allocation patterns also differed consistently between the two groups. Invasive plants maintained or increased allocation to aboveground tissues, resulting in sustained gains in plant height and total biomass, while native plants increasingly shifted allocation belowground without corresponding biomass gains. Trait-based percentage changes further revealed that positive responses in key growth traits were consistently greater in invasive than in native species across successive fluctuation cycles. These results demonstrate that repeated heat fluctuations can amplify performance asymmetries between invasive and native plants, highlight the importance of heatwave-like thermal regimes as a driver of invasion success under climate change.