Studies on decomposition ofPhragmites australis leaves under laboratory conditions

Summary The decomposition ofPhragmites leaves was studied under experimental conditions in vessels during 147 days. This process was compared in vessels filled with (a) lake water, (b) lake water and sediment, and (c) lake water, sediment and plant material.In the course of time the ash-free dry weight and the N and C concentration in the plant material decreased gradually to, respectively, 64, 54 and 66% of the initial values. The P concentration fluctuated due to accumulation of bacteria and their excretion products. Almost all C and N which had disappeared from the plant material during the first 100 days of incubation was recovered in the water. Subsequently, these nutrients accumulated in the sediment. Only 10% of the C and N in the water was soluble (<0.33 m). Ortho-P increased substantially from 60 to 100 days of incubation in the vessels (b) and (c), possibly given off by the sediment or originating from decaying algae and bacteria. Only a minor part of the plant-P was recovered as ortho-P in the water.The effect of the decomposing plant material on the diversity within the microscopical primary producers was studied using paper chromatography of the pigments. The changes in bacterial numbers were followed by epifluorescence microscopy.