Differential Responses in Wedelia trilobata and Wedelia chinensis Under Light Stress: Roles of Abscisic Acid and Sodium Tungstate

Light availability is a primary determinant of plant growth and a key factor influencing the success of alien plant invasions. Although the phytohormone abscisic acid (ABA) is a known master regulator of abiotic stress responses, its specific role in the shade tolerance and competitive advantage of invasive species remains poorly understood. In this study, we conducted a comparative experiment using the highly invasive Wedelia trilobata and its native congener, Wedelia chinensis. We investigated their eco-physiological responses to normal (100%) and low-light (30%) intensities, coupled with the application of exogenous ABA (A1) and the biosynthesis inhibitor sodium tungstate (S1). Our results showed that low light significantly inhibited the growth and photosynthetic capacity of both species, reducing biomass and net photosynthetic rate Pn. However, exogenous ABA application specifically enhanced the Pn and biomass of the invasive W. trilobata under low-light stress, while reducing malondialdehyde (MDA) content and optimizing antioxidant enzyme activities (SOD, POD, and CAT). Conversely, the inhibition of endogenous ABA by sodium tungstate exacerbated oxidative damage and photosynthetic decline in both species, with a more pronounced negative impact on W. trilobata. Correlation analysis further revealed that W. trilobata maintains a superior capacity to coordinate stomatal regulation and antioxidant defense through ABA signaling. These findings suggest that the invasive success of W. trilobata in fluctuating light environments is significantly driven by its high sensitivity and efficiency in ABA-mediated physiological plasticity, providing a potential target for managing its spread through hormonal or metabolic interference.