Seasonal Modulation of Salinity Stress Response in Leaf Micro-morphological and Biochemical Insights of the Mangrove Avicennia sp. (Acanthaceae) in Digha Mohona, West Bengal

Seasonal variations (pre-monsoon and monsoon) cause minor shifts in the mangrove microenvironment, including average temperature, pH, salinity, TDS, and EC in both surface water and soil. These fluctuations lead to subtle alterations in mangrove micro-morphology (salt gland index) and influence the accumulation of compatible osmolytes (CO) such as proline, glycine betaine (GB), and sugar alcohols (mannitol and sorbitol). Seasonal changes also affect plant pigments, soluble sugars, and the accumulation of secondary metabolites in plant tissues. In this study, we examined how mangrove species adapt to their microenvironment by assessing along with SGI, CO, plant pigment and secondary metabolites (TPC, TFC and TPPC) accumulation in plant tissues. The biochemical composition of CO, along with the seasonal accumulation pattern was also species-specific. CO levels were highest during the pre-monsoon season and lowest during the monsoon. A. rumphiana showed the highest proline concentration in the pre-monsoon season, while GB accumulation was highest in A. rumphiana and A. alba . Similarly, the secondary metabolite accumulation pattern along with their seasonal variation exhibited species-specific manner and plant developmental phases. The highest level of TPC was found in A. rumphiana during pre-monsoon. Whereas A. marina and A. alba displayed the highest TPC in post-monsoon. A significant decrease in the chlorophyll content in pre-monsoon, while soluble carbohydrate accumulation was more pronounced during the monsoon and post-monsoon seasons. These patterns show how different species have adapted to shifting environmental circumstances.