Differences in the Ecophysiological Traits of Dominant Mangrove Rhizophora mucronata Lam. across Three Geographical Sites

Localised changes in environmental factors shape species distribution and characteristic traits of the plants. This study investigated the morpho-physiological and biochemical trait variations of Rhizophora mucronata Lam. across three distinct geographical locations in Kerala, India: Thalassery (T site), Mogral Puthur (M site), and Nileshwaram (N site) to assess site-specific responses to environmental factors. Observed variations at Nileshawaram are primarily attributed to site-specific environmental variables influenced by higher sodium concentrations, increased soil and water electrical conductivity, and alkaline water. Key traits, including leaf weight, laminal length, propagule thickness, leaf dry weight, petiole length, petiole index, and leaf pigments (chlorophyll a, b, total chlorophyll, carotenoids, and beta-carotene), leaf dry mass/unit area, and specific leaf area (SLA) were significantly (P < 0.05) lower at the N site compared to T and M sites. Antioxidants, such as, total flavonoids, polyphenols, and tannins were also reduced at the N site. The reduced leaf pigment and antioxidants suggest a compromised oxidative stress response, potentially indicating elevated reactive oxygen species (ROS) levels in N site leaves. Notably, over 70% of the propagules from the N site exhibited distinctive hook-like structures, which were absent in the other two sites. In the Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectral analysis, functional groups for polyphenols, chlorophyll, phenol, and flavonoids were detected in leaves. These findings revealed that changes in environmental conditions might have impacted R. mucronata leaves, serving as the indicator tissues. This study offers critical insights into population-level responses and holds important implications for mangrove forest conservation under varying environmental stressors.