Flooding adaptations of wetland trees

A reduction in gas exchange between the air and the rhizosphere causes a major problem for terrestrial plants (Jackson & Drew 1984; Visser & Vosenek 2004). Soil flooding or submergence sets in motion a series of physical, chemical, and biological processes that profoundly influence the quality of soil as a medium for plant growth (Ponnam peruma 1984). In well-drained soils, the stability of the gas composition is maintained by rapid gas exchange between the soil and air, despite oxygen consumption, carbon dioxide production, and nitrogen fixation by soil organisms. In contrast, soil flooding or submergence causes oxygen depletion and carbon dioxide accumulation in the rhizosphere and plants (Jackson & Drew 1984; Ponnamperuma 1984; Greenway et al. 2006). These events lead to an energy deficit in plants through the inhibition of aerobic respiration and disturbance of photosynthetic processes. The accumulation of phytotoxic compounds, including reduced forms of iron and manganese, ethanol, lactic acid, acetaldehyde, aliphatic acids, and cyanogenic compounds, is also a major problem for plants (Ponnamperuma 1984). The effects of such compounds on root metabolism cause the inhibition of root growth and development (Jackson & Drew 1984; Ponnamperuma 1984; Armstrong et al. 1996; Armstrong & Armstrong 1999; Pezeshki 2001; Greenway et al. 2006). Thus, vegetation in the peripheral zone of lakes and swamps typically consists of flood-tolerant species that have specific mechanisms to tolerate excessive water.