Biotic Uptake and Release of Phosphorus by a Wetland Sediment

Abstract

Abstract Currently there is considerable controversy about the role of bacteria in the direct uptake and release of phosphorus by sediments. This paper reports work aimed at testing the hypothesis that microbial uptake and release of phosphorus by sediments is an important process in wetlands and that this process is influenced by the type of organic matter in the sediment. Experiments were undertaken with a wetland sediment to which was added both a carbon source (glucose or acetate) and orthophosphate (P). The carbon sources were chosen to represent a simple available carbon source (glucose) and a fermentation product (acetate). Control experiments were also undertaken using a sterilised sediment with P added and an unsterilised sediment without added P. Under aerobic conditions, 100% of the added orthophosphate was taken up biologically by both the organic carbon-amended sediments, with 34–45% of this estimated to be microbial uptake. A smaller amount (ca. 9%) of the added phosphorus was taken up biotically by sediments that had no added carbon. When these aerobic uptake experiments were made anaerobic (and additional organic carbon added), only the acetate-amended sediment released an appreciable amount (ca. 30%) of the initially added phosphorus. We postulate that the acetate-amended sediment took up P for cell growth and also stored some P as polyphosphate (poly-P). This poly-P was then released under anaerobic conditions. The glucose-amended sediment used the added P for cell growth only, and this phosphorus was not released when the sediment was made anaerobic for a period of 10 days. These preliminary results suggest an important additional role for sediment bacteria in the cycling of phosphorus. In the presence of bioavailable organic carbon (e.g. glucose) and orthophosphate, sediment bacteria can grow well under aerobic conditions but do not seem to release the phosphorus under anaerobic conditions (at least not within the 10 days of the experiments reported here). However, in the presence of acetate, it appears the 'luxury uptake' of added phosphorus can occur under aerobic conditions, and that this poly-P is released when the sediments are made anaerobic. More work is needed to determine the relative importance of these microbial uptake and release mechanisms in different sediment environments. Keywords: Abioticacetatebioticuptakereleaseglucosephosphoruspoly-P bacteriaredox conditionssedimentwetlands