EFFECTS OF LITTER ON SUBSTRATE CONDITIONS AND GROWTH OF EMERGENT MACROPHYTES

Three successive emergent macrophytes (Typha latifolia L., Phragmites australis (Cav.) Steudel and Glyceria maxima (Hartman) Holmbly) were e ach grown in substrates collected from three different zones of shorel ine vegetation development (non-vegetated sediment, the interface betw een T. latifolia and P. australis, and degenerating P. australis). The aim of the study was to assess whether accumulation of litter changes growth conditions of P. australis, and to determine its effects on pr e- and post successional plant species. The study was carried out by m eans of pot experiments in a glasshouse. Seedlings of the three specie s were cultured in fertilized and unfertilized substrates under both w aterlogged and drained conditions. In its own litter, growth of P. aus tralis was strongly reduced, compared with the productivity of plants in substrates from preceeding successional stages, and could not be co mpensated for by fertilization or soil drainage. The redox potential o f the substrate was not strongly reduced and the sediment density was well above the critical level. Soil sterilization by gamma-irradiation did not improve growth substantially, although there was some positiv e effect in unfertilized substrate. Phytotoxic compounds might have ca used poor growth of P. australis in its own litter. T. latifolia and G . maxima were relatively less affected by the P. australis litter. The possible importance of litter accumulation on species replacement in shoreline vegetation is discussed. It is concluded that the accumulati on of organic matter should be considered as a factor affecting spatio -temporal processes in littoral vegetation owing to its specific impac t on the functioning of individual dominant plant species.