Flooding Resistance of Rhizomatous Amphibious Plants

Marsh plant rhizomes are subjected naturally to prolonged periods of oxygen deficiency by flooding. They usually exhibit a remarkable flooding resistance consisting of avoidance and tolerance strategies. The adverse effects of flooding are mainly avoided by oxygen diffusion through porous tissues and by the release of small amounts of oxygen. In shooted rhizomes of all species investigated so far, oxygen transport sustains aerobic respiration, be it in some cases at a very low rate. In the central part of rather dense rhizomes, aerobic respiration may coincide with fermentation processes. Variation between species in rhizome tolerance of anoxia is great. It can range from a few days to several months dependent on the season. Some species are able to extend shoots under strictly anoxic conditions. With respect to anoxic metabolism very few generalisations are possible. Alcoholic fermentation is the dominant energy-yielding process and one of the major factors determining anoxia endurance is the content of storage products. In winter, very tolerant species, such as Schoenoplectus lacustris and Acorus calamus, accumulate large amounts of nitrogen-rich amino acids, such as arginine and asparagine. The ability to synthesize macromolecules under anoxia, is probably very different for different species, which may reflect the phylogenetic variability of adaptation strategies developed in wetland plants