Decomposition of Potamogeton crispus L.: The effects of drying on the pattern of mass and nutrient loss

A study was made of the pattern of decomposition of Potamogeton crispus L., contained in gauze bags which were incubated in the field. Plant material was collected from the field when the population began its annual decline. Either by placing the material directly into bags or by air-drying first, it was possible to compare the patterns of mass and nutrient loss following natural senescence, with that following unnatural death. Natural senescence and decay was characterized by a linear and rapid loss of mass (4% day −1) while dried plants showed a rapid initial loss (18% in 2 h) followed by a slower loss (2% day −1). However, the overall rate of mass loss from dried plants was slower than that of senescent plants with 35 and 10% of the original mass remaining after 24 days, respectively. There was little change in the nutrient status of the senescent material during the experiments. However, marked changes in the P and K concentrations (attributed to leaching) and Ca and Mg concentrations (attributed to adsorption) occurred in the dried material within 2 h. Losses of nutrient stocks were also markedly altered by drying. These rapid changes in nutrient status of the dried material appeared to discourage colonization by detritivorous snails and reduce microbial catabolism of the plant tissues. The slower rate of loss from the bags would thus be attributed to the different pathways of energy and nutrient transfer which became operative when plant material was dried. Different mathematical functions were required to define the two decomposition rates and it was clear that interference with the events of senescence by drying of the normally submerged plants could impinge on the predictive potential of such models. It is concluded that in aquatic, particularly submerged macrophyte communities, the processes of detritus production and utilization cannot be considered in isolation from the preceding process of senescence.