Differential responses to cadmium stress and competition in Alternanthera philoxeroides and Trifolium repens: stress resistance and adaptive strategies

Abstract Background Heavy metal pollution, a pervasive and persistent environmental stressor often linked to industrial and agricultural activities, interacts with intra- and interspecific competition as key factors influencing the invasion of exotic plants. Alternanthera philoxeroides and Trifolium repens exhibit distinct allocation strategies to mitigate resource competition under cadmium (Cd) pollution, yet their differential resistance to Cd remains underexplored. Results In this study, a greenhouse experiment was conducted to investigate the effects of Cd contamination and competitive interactions on the stress resistance index (SRI) and adaptive strategies of both species. The results indicated that T. repens exhibited higher SRI under stronger interspecific competition, demonstrating clear density dependence. T. repens primarily enhanced its competitiveness by increasing photosynthesis capacity, though its root system structure contributed more substantially to SRI. In contrast, A. philoxeroides increased SRI by forming shorter and thicker root system. Conclusion Overall, the root utilization strategy of A. philoxeroides showed greater advantages than that of T. repens . Under intraspecific competition, A. philoxeroides improved competitiveness mainly through increased root complexity and optimized photosynthetic efficiency via non-stomatal regulation in light competition. The invasiveness of A. philoxeroides can be attributed to the ability to synergistically combine root development and photosynthesis to enhance its stress resistance. This study provides a broader perspective on invasion mechanisms in natural ecosystems and offers a solid theoretical basis for understanding stress tolerance and environmental management of A. philoxeroides .