Ecophysiology of wetland plant roots: A modelling comparison of aeration in relation to species distribution

This study examined the potential for inter-specific differences in root ae ration to determine wetland plant distribution in nature. We compared aerat ion in species that differ in the type of sediment and depth of water they colonize. Differences in root anatomy, structure and physiology were applie d to aeration models that predicted the maximum possible aerobic lengths an d development of anoxic zones in primary adventitious roots. Differences in anatomy and metabolism that provided higher axial fluxes of oxygen allowed deeper root growth in species that favour more reducing sediments and deep er water. Modelling identified factors that affected growth in anoxic soils through their effects on aeration. These included lateral root formation, which occurred at the expense of extension of the primary root because of t he additional respiratory demand they imposed, reducing oxygen fluxes to th e tip and stele, and the development of stelar anoxia. However, changes in sediment oxygen demand had little detectable effect on aeration in the prim ary roots due to their low wall permeability and high surface impedance, bu t appeared to reduce internal oxygen availability by accelerating loss from laterals. The development of pressurized convective gas flow in shoots and rhizomes was also found to be important in assisting root aeration, as it maintained higher basal oxygen concentrations at the rhizome-root junctions in species growing into deep water. (C) 2000 Annals of Botany Company.