Intraspecific trait variation of a floating macrophyte, Nymphaea rudgeana G.Mey. (Nymphaeaceae), across different river basins in the Eastern Amazon

The variability of plant traits within a single species, driven by adaptation and phenotypic plasticity, enhances an individual's ability to survive under changing conditions. While intraspecific trait variation (ITV) is recognized as a key driver of plant adaptation, how aquatic plants modulate their functional strategies across distinct regional and local environmental gradients remains poorly understood. We evaluated the ITV of Nymphaea rudgeana across two Amazonian River basins (Acará-Guamá and Gurupi), measuring leaf morphological traits and petiole length in 56 individuals across 19 sites. Our results showed that ITV varied across traits, with leaf area (LA) and specific leaf area (SLA) exhibiting greater plasticity than leaf dry matter content (LDMC) and petiole length. Interestingly, large-scale regional differences (river basins) weakly explained trait variation. Instead, local environmental factors were the primary drivers of ITV. Environmental conditions such as water depth, temperature, and sediment chemical composition (e.g., sodium and aluminum), triggered distinct strategic shifts, by modulating leaf expansion and resource investment toward either acquisitive or conservative strategies. Overall, N. rudgeana exhibited varying phenotypic responses to environmental variation rather than regional boundaries. Our findings emphasize the importance of local environmental factors over regional differences in shaping aquatic plant ITV, with implications for predicting macrophyte responses to habitat alterations and climate change. Further research should consider genetic differentiation and plasticity to better understand ITV patterns in widely distributed aquatic species.