Physiological and biochemical responses of Egeria densa to different sediment redox conditions

Under anaerobic or low oxygen regimes of aquatic environments, the sediment redox condition is one of the major abiotic stresses for plant growth and plays an important role in the distribution of species. In this study, we assessed the effects of reduced conditions, and macro and microelements associated with different redox-potential regimes on a submerged macrophyte, Egeria densa , in a microcosm experiment. Five treatments, namely, control (C), reduced (R), highly reduced (HR), transferred water from a reduced tank (RW), and transferred water from a highly reduced tank (HRW) were tested. To assess the effect of H2 S, E. densa was exposed to five NaHS (H2 S donor) concentrations (viz. , 0, 0.01, 0.05, 0.1, and 0.2 mM NaHS) in a separate microcosm experiment. The concentrations of macro and microelements in the experimental microcosms increased significantly compared to the control in the process of attaining R and HR treatment conditions. Plants exposed to low redox environments showed a significant reduction in the growth rate, photosynthetic pigments, and indole acetic acid; those treatments also showed an excess generation of hydrogen peroxide, peroxidase activities, catalase activities, and ascorbate peroxidase activities compared to plants exposed to the control. Our study suggests that in reduced conditions, low oxygen and high CO2 concentrations result in a stress that has stronger effects on plants in terms of stress responses compared to soluble macro and microelements. This study will improve our ability to predict the dynamics of wetland aquatic vegetation and thus facilitate the formulation of wetland management and restoration strategies.