Experimental flooding modifies rhizosphere conditions, induces photoacclimation and promotes antioxidant activities in Rhizophora mucronata seedlings

Abstract

Abstract Survival of mangrove seedlings under flooding depends on their tolerance and adaptation. This study investigated the effects of flooding on rhizosphere conditions: porewater dissolved oxygen (DO), pH, and soil oxidation–reduction potential (ORP) and photosynthetic and antioxidant activities (superoxide dismutase [SOD] and guaiacol peroxidase [POX] activity and glutathione [GSH] content) of Rhizophora mucronata seedlings. The experiment lasted 20 days with three treatments: control (with drainage), waterlogging (10 cm of water above the soil surface) and submergence. Our results demonstrate that waterlogging and submergence resulted in a reduction in porewater DO, pH and soil ORP from day 5 into the treatment. Submergence resulted in lower maximum electron transport rates, lower saturating irradiance and higher light utilization efficiency from day 5 onwards, but stomatal closure was detected in both flooded treatments. POX activity and GSH content in the roots were increased by submergence. On day 5, submerged plants showed higher root POX activity than the other two treatments and higher root GSH content than controls. However, these parameters decreased on day 20, so that no difference among the treatments remained. As persistent flooding was shown to hamper the physiological performance of mangrove seedlings, extreme weather events and sea-level rise should be closely monitored.