Drought-induced metabolic dysregulation significantly enhances the production of reactive oxygen species (ROS), which, in turn, exerts a substantial influence on the oxidation–reduction regulatory status of cells. These ROS, under conditions of drought stress, become highly reactive entities capable of targeting various plant organelles, metabolites, and molecules. Consequently, disruption affects a wide array of metabolic pathways and eventually leads to the demise of the cells. Given this understanding, this study aimed to investigate the effects of different drought stress levels on the growth and development of the invasive weed Wedelia trilobata and its co-responding native counterpart Wedelia chinensis. Both plants evolved their defense mechanisms to increase their antioxidants and hormone contents to detoxify ROS to avoid oxidative damage. Still, the chlorophyll content fluctuated and increased in a polyethylene-glycol-simulated drought. The proline content also rose in the plants, but W. chinensis showed a significant negative correlation between proline and malondialdehyde in different plant parts. Thus, W. trilobata and W. chinensis exhibited diverse or unlike endogenous hormone regulation patterns under drought conditions. Meanwhile, W. trilobata and W. chinensis pointedly increased the content of indole acetic acid and gibberellic acid in a different drought stress environment. A positive correlation was found between endogenous hormones in other plant parts, including in the roots and leaves. Both simulated and natural drought conditions exerted a significant influence on both plant species, with W. trilobata displaying superior adaptation characterized by enhanced growth, bolstered antioxidant defense mechanisms, and heightened hormonal activities.

Salinity is one of the most significant environmental factors limiting plant development and productivity. Invasive plants could quickly respond to environmental changes, thus successfully achieving invasion. However, there is limited research on the mechanism of salt responses in invasive plants under different nutritional conditions. This study evaluated and compared the impact of salinity stress and nutrient application on physiological responses in the invasive plant Wedelia trilobata and native plant Wedelia chinensis. Mild salinity stress disrupted the growth of these two plants, significantly reducing their leaf and stem node number under a low nutrient condition. W. trilobata showed notable decreases in height and leaf number with high salinity stress regardless of nutrient levels, whereas it was observed only in the low nutrient state in W. chinensis. The negative effects of high salinity on both species were most evident in nutrient-poor environments. Under low salinity and nutrient stress, W. trilobata’s leaves exhibited increased levels of proline, MDA, CAT, and ABA, with decreased GA and IAA content. A low-salt environment favored W. trilobata’s competitive advantage, and nutrient enrichment appeared to enhance its invasive potential, in which process the plant antioxidant system and endogenous hormones contribute greatly. This study provides a theoretical foundation for predicting suitable growth areas for W. trilobata referring to the salt condition, guiding future strategies for preventing and controlling its invasive spread.

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 P_n. However, exogenous ABA application specifically enhanced the P_n 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.