Physiological adaptations to wetland habitats

Abstract

Low gas-diffusivity and oxygen-solubility in water are primary constraints in wetland and aquatic environments. Consequentially, microbes may remove oxygen from all but surface layers of waterlogged soils and generate phytotoxins, while shoot-submergence may substantially reduce CO 2 -availability for photosynthesis, compromising carbohydrate production. Oxygen limitations may cause energy crises within the plant and self-generation of damaging reactive oxygen species; enhanced generation and entrapment of the gaseous hormone ethylene also accom- pany waterlogging and submergence. Globally, wetlands differ in altitude, timing, duration and depth of flooding, light, temperature, and biogeochemistry. Conse- quently, suites of adaptive traits have evolved in plants to accommodate these varied conditions. Adaptations include anoxia avoidance by facilitating gas exchange with the atmosphere to support aerobic metabolism, an emergence escape strategy or a medium-term submergence tolerance strategy, or production of leaves capable of photosynthesis when submerged. Other adaptations include short- or long-term anoxia tolerance or protection from reactive oxygen species and phytotoxins.