Wetland plant responses to soil flooding

Wetland plants possess various characteristics that enable them to survive periodic soil saturation and the accompanying changes in soil chemistry. These changes include the lowering of soil redox potential (Eh) which translates into a progressively greater demand for oxygen within the soil and hence additional stress on the roots. However, information on the relationship between flood-response of wetland plants and reducing soil conditions is limited. In particular, the relationship between soil reduction and plant photosynthesis is largely unknown. but the literature reveals a range of photosynthetic sensitivities to the intensity of soil reduction among wetland species. Initial reductions in net photosynthesis immediately after soil flooding are common among species representing various wetland ecosystems including marshes. forested wetlands, and riparian wetlands. At the whole-plant level, the photosynthetic reductions are attributed to diffusional limitations due to stomatal closure and to metabolic (non-stomatal) inhibition of photosynthesis. Low soil Eh may lead to photosynthetic reduction due to decreased leaf water potential resulting from root dysfunction, reduced activity of major photosynthetic enzymes. disruption in photosynthate transport, alteration in source-sink relationship or reduced sink demand. Furthermore, while root oxygen-deficiency may partially account for the reduction in net photosynthesis, soil phytotoxins produced as by-products of low soil Eh conditions may play a major role in the observed photosynthetic sensitivities. Clearly, the high oxygen demand in soil resulting from intense reduction exerts profound influence on oxygen transport and release to the rhizosphere. However. methods are needed to differentiate wetland plant responses to low oxygen conditions and soil phytotoxins that are byproducts of soil reduction. (C) 2001 Elsevier Science B.V. All rights reserved.