Physiological adaptations of Hymenachne amplexicaulis to flooding.
The introduced grass Hymenachne amplexicaulis has been established for use in ponded pastures in Central Queensland. However, its ability to out-compete native species and invade wetlands also makes it a potential weed. To determine the characteristics that make it a successful ponded pasture species, the adaptation of H. amplexicaulis to flooding has been investigated. The growth and development of H. amplexicaulis under flooded and non-flooded conditions was compared in a series of experiments carried out in three 2-m high galvanized steel tanks. Leaf, stem and root sections were taken to determine the timing and extent of aerenchyma formation. The effect of flooding on the pattern and distribution of growth was also determined. Hymenachne amplexicaulis is adapted to flooding because it has the capacity for rapid elongation of the stem and the formation of adventitious roots. Aerenchyma was present in stem, leaf and root tissues in both flooded and non-flooded plants. The aerenchyma would provide buoyancy as well as aiding the circulation of gases. When the plants were flooded, submerged leaves senesced rapidly and the previously exposed, but now submerged nodes produced adventitious roots. Under flooding, the growth of leaves increased at the expense of the roots, presumably maintaining the effective photosynthetic leaf area. The implications and limitations of these adaptations are discussed.