Effects of sediment type and water level on biomass production of wetland plant species

We investigated how water level and different sediment types affect the gro wth of wetland plant species. Twelve different species were grown in draine d and waterlogged sediments, which represented types normally encountered i n wetlands: a mineral sediment from exposed sites, a sediment from a shelte red site rich in labile organic matter and an organic sediment with decompo sing litter of Phragmites australis (Cav.) Steudel. The tested species incl uded both subordinate and dominant species inhabiting flooded or dry parts of the water-depth gradient. Due to nutrient limitation, biomass production of most species was lowest i n the mineral sediment. In this substrate waterlogging only affected Cirsiu m arvense and Eupatorium cannabinum which were reduced to 30% and 16% of th e production in the drained sediment. Most species performed best in the se diment with labile organic matter, even when waterlogged. Waterlogging in t he reed litter sediment, when compared to the drained reed litter, decrease d growth of six species: Iris pseudacorus by 40%, Myosotis scorpioides by 6 0%, Rorippa amphibia by 25%, Sium latifolium by 50%, Eupatorium cannabinum by 80%, and Epilobium hirsutum by 70%. The differences in plant performance between both organic sediments may be due to the presence of refractory or ganic matter. The specific responses in the reed litter sediment contrasted with the similar response to both other sediments. These results show that accumulation of litter, instead of accumulation of organic matter in,gener al, will be an important factor in determining species composition of litto ral zones. They also indicate that, although litter does not favor subordin ates above clonal dominants, litter accumulation may enhance species divers ity on a large scale. (C) 1999 Elsevier Science B.V. All rights reserved.