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Nutrient resorption efficiency is an important nutrient conservation and ecophysiological mechanism of mangroves growing in saline environments. This study investigated the nitrogen, phosphorus, and potassium resorption efficiency of Avicennia officinalis L. growing across a salinity gradient with seasonal variations in the Sundarbans of Bangladesh. Due to decreasing salinity during the monsoon and postmonsoon seasons, the nutrient availability in soil and nutrient resorption efficiency did not vary significantly among the low-salinity, medium-salinity, and high-salinity zones. However, the nutrient availability in the medium-salinity and high-salinity zones was significantly lower than that in the low-salinity zone during the premonsoon season due to increased salinity. Consequently, nutrient resorption efficiency in the medium-salinity and high-salinity zones was significantly higher than that in the low-salinity zone during the premonsoon. Further, leaf vein density of A. officinalis in the medium-salinity and high-salinity zones was significantly higher than that in the low-salinity zone. This modification in vein density was the mechanism for the higher nutrient resorption efficiency of A. officinalis in the medium-salinity and high-salinity zones than that in the low-salinity zone. This plasticity in nutrient resorption efficiency is a physiologically adaptive mechanism that enables A. officinalis to persist in increasingly saline environments due to climate change.