Abstract: The invasive plant Dolichandra unguis-cati (L.) L. G. Lohmann has exhibited rapid expansion across Guangdong and Fujian provinces in China, posing a significant threat to native ecosystems. To investigate its adaptive strategies and physiological responses under varying habitats, a controlled experiment was conducted using D. unguis-cati seedlings subjected to three soil moisture regimes (W1–W3: 30%, 60%, 90%) and four light intensities (L1–L4: 0%, 30%, 60%, 100%). Photosynthetic parameters and biochemical traits were assessed to evaluate plant performance under single and combined stressors. Results indicated that low water content in the soil (W1, 30%) and complete darkness (L1) significantly inhibited photosynthetic activity and induced cellular oxidative stress, as evidenced by elevated malondialdehyde (MDA) levels. In response, antioxidant activity was maximized to eliminate free radicals and protect against damage. Under sufficient water and light, seedlings exhibited rapid accumulation of soluble sugars and starch. Photosynthetic efficiency, indicated by F_v/F_m and F_v/F₀, was highest under L3 light intensity in the W2 and W3 treatments. Gas exchange parameters and antioxidant enzyme activities displayed high phenotypic plasticity across treatments, with catalase (CAT) showing the greatest plasticity index (0.963). Based on principal component analysis, the top three performing treatment combinations were those under L3 light intensity, with the W3L3 treatment yielding the most favorable physiological profile. These findings indicate that D. unguis-cati seedlings prefer moist and moderately lit conditions, where both germination and growth are optimized, although the species retains a degree of resilience under water and light stress.