Interactions Between Oxygen-Releasing Roots and Microbial Processes in Flooded Soils and Sediments

Abstract

It is hard to imagine that wetland soils and sediments are adverse habitats for plant growth, considering the diverse vegetation that flourishes in fresh- and salt-water marshes (tidal as well as non-tidal), bogs, fens, forested swamps, and floodplains. However, the permanent or periodic flooding of soils or sediments has a number of physical, chemical and biological consequences for the soil/sediment environment (e.g. Ponnamperuma 1984; Gambrell et al. 1991). The most important ramification of the water layer on top of flooded soils and sediments is the restricted entry of atmospheric oxygen. The diffusion of oxygen in water is 10,000 times slower than in air. Oxygen is rapidly depleted in the upper layers of inundated soil due to chemical and biological oxidation processes, resulting in a soil profile where the presence of oxygen is limited to the upper mm’s (e.g. Frenzel et al. 1992; Lorenzen et al. 1998). Plants have developed various mechanisms to equip them for colonisation and growth in anoxic flooded soils and sediments, as reviewed elsewhere (Drew 1983; Armstrong et al. 1994; Blom and Voesenek 1996; Blom 1999). Changes in anatomy, morphology and metabolism are of paramount importance for surviving in anoxic root environments. The most important adaptation is the development of aerenchyma, which creates a gas-space continuum that stretches from the stornata to the root-root cap junction, referred to as aerenchyma.