Growth responses and metabolic adaptations to sugar mill effluents in Terminalia arjuna

This study examined the growth performance, physiological and biochemical responses, and phytoremediation potential of Terminalia arjuna across sugar mill effluent (SME) concentrations (0, 10, 25, 50, 75, and 100%). Physicochemical characterization of the SME indicated elevated heavy metals and other toxic constituents. A pot experiment showed that at a 10% effluent concentration, plants experienced significant increases in shoot and root lengths, biomass, and photosynthetic pigments, with only slight changes in stress indicators. However, increasing the effluent concentration to 25-75% led to declines in growth and pigment production, along with an increase in biochemical stress markers. At the highest effluent concentration (100%), pronounced reductions were recorded in morphological traits, with shoot length decreasing by 86%, root length by 55%, fresh weight by 90%, and dry weight by 136% compared with the control. Photosynthetic pigments were also strongly affected, including chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids. Non-protein thiols declined, whereas oxidative stress indicators such as hydrogen peroxide and lipid peroxidation increased substantially. In response to effluent-induced stress, antioxidant defense mechanisms were activated, with enhanced activities of superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (G-POD), and ascorbate peroxidase (APX). Heavy metal analysis revealed high accumulation in plant roots, surpassing concentrations in shoots. The findings indicate that T. arjuna can tolerate and accumulate heavy metals from sugar mill effluent. This study is the first to detail its adaptations under SME stress and to emphasize its potential for phytoremediation of contaminated environments.