Response of biomass allocation and major stem‒leaf traits in Ageratina adenophora to heterogeneous habitats in the lakeside zone of Qionghai Lake, Western Sichuan Plateau, China

To clarify the adaptive strategies of invasive plants in heterogeneous lakeside habitats, this study investigated the coordinated responses of biomass allocation and stem-leaf traits of Ageratina adenophora along an environmental gradient in Qionghai Lake’s lakeside zone. According to differences in habitat conditions, the A. adenophora community was divided into three plots: near the shore area (plot I: 50 ~ 150 m from the shore, a groundwater depth of 0.30–0.50 m), middle shore area (plot II: 200 ~ 300 m from the shore, a groundwater depth of 0.50–0.75 m), and remote shore area (plot III: 350 ~ 450 m from the shore, a groundwater depth of 0.75–1 m). Using linear mixed-effects models, multiple stepwise regression, and Mantel tests, we analyzed trait variations and their environmental drivers. The results revealed that along the gradient from near shore to remote shore, A. adenophora shifted from prioritizing aboveground to underground allocation, with root-shoot ratio (RSR) exhibiting the highest plasticity. Stem-leaf traits transitioned from resource-conserving (thin long stems, small leaves) to resource-acquiring (thin short stems, large leaves with high SLA) characteristics. Soil available potassium (SAK) and pH were dominant drivers, with SAK promoting growth-related traits and pH exerting inhibitory effects. Mantel tests confirmed a significant overall association between trait and environmental matrices (r = 0.495, p = 0.001). In heterogeneous habitats, invasive plants in the lakeside zone achieve coevolution of stem and leaf morphological components by balancing the allocation of root and shoot biomass and increasing the success rate of their colonization. This reflects the strong morphological plasticity mechanism and biomass allocation strategy of invasive plants in the lakeside zone. This study reveals that A. adenophora achieves successful colonization via coordinated trait plasticity mediated by key soil factors, providing a scientific basis for targeted management of invasive plants in lakeside zones.