Intraspecific trait variation and resource allocation trade-offs under water stress unveil divergent survival strategies in emergent macrophytes amid climate change

Human-induced climate change threatens ecosystems, with altered precipitation regimes causing extreme events like flooding and droughts that impact plant traits such as biomass allocation (to aboveground or belowground) and reproductive strategies. These shifts reflect plants’ responses to environmental stress, and such changes in macrophyte traits can affect freshwater ecosystem processes such as productivity and nutrient cycles. Examining intraspecific trait variation (ITV) in macrophytes under climate change is critical to predicting freshwater ecosystem dynamics. However, how macrophytes adjust their ecological strategies to varying water availability remains unclear. In this study, we investigated ITV and biomass allocation trade-offs in Limnocharis flava and Pontederia rotundifolia in a greenhouse experiment where individuals were subjected to flooding and drought conditions. We analyzed traits spanning physiology, morphology and phenology. We hypothesized that drought would induce conservative strategies, while flooding would elicit acquisitive strategies with coordinated organ-level trait responses. Our results revealed species-specific strategies. Individuals of L. flava combined drought escape and avoidance with flood escape, allocating biomass belowground during drought and aboveground during flooding. In contrast, individuals of P. rotundifolia showed osmotic adjustment under drought, maintaining metabolism despite water limitation, and a shift toward vegetative reproduction. Under flooding, individuals directed biomass to roots, reflecting drought tolerance and flood escape strategies. These findings highlight the critical role of ITV in plant survival under contrasting environments, emphasizing species-specific adaptations to water stress. Understanding ITV within populations and communities is essential for conserving biodiversity, particularly in vulnerable freshwater ecosystems, as climate change intensifies.