Effects of litter on substrate conditions and growth of emergent macrophytes

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Abstract
Summary: Three successive emergent macrophytes (Typha latifoliaL.,Phragmites australis(Cav.) Steudel andGlyceria maxima(Hartman) Holmbly) were each grown in substrates collected from three different zones of shoreline vegetation development (non‐vegetated sediment, the interface betweenT. latifoliaandP. australis, and degeneratingP. australis). The aim of the study was to assess whether accumulation of litter changes growth conditions ofP. australis, and to determine its effects on pre‐ and post successional plant species. The study was carried out by means of pot experiments in a glasshouse. Seedlings of the three species were cultured in fertilized and unfertilized substrates under both waterlogged and drained conditions.In its own litter, growth ofP. australiswas strongly reduced, compared with the productivity of plants in substrates from preceeding successional stages, and could not be compensated for by fertilization or soil drainage. The redox potential of 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 positive effect in unfertilized substrate. Phytotoxic compounds might have caused poor growth ofP. australisin its own litter.T. latifoliaandG. maximawere relatively less affected by theP. australislitter. The possible importance of litter accumulation on species replacement in shoreline vegetation is discussed. It is concluded that the accumulation of organic matter should be considered as a factor affecting spatio‐temporal processes in littoral vegetation owing to its specific impact on the functioning of individual dominant plant species.