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 that includes average temperature, pH, salinity, total dissolved solids, and electrical conductivity 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 salt gland index, CO, plant pigment, and secondary metabolite (total phenol content (TPC), total flavonoids content (TFC), total polyphenol content (TPPC)) accumulation in plant tissues. The biochemical composition of CO, along with seasonal accumulation pattern, was also in a species-specific manner. CO levels were highest during the pre-monsoon season and lowest during the monsoon season. A. rumphiana showed the highest proline concentration in the pre-monsoon season, while GB accumulation was highest in A. rumphiana and A. alba . Similarly, secondary metabolite accumulation pattern, along with their seasonal variation, exhibited a species-specific manner and plant developmental phase. 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 season. A significant decrease was noted in the chlorophyll content in the pre-monsoon season, 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.