Response of sediment bacterial communities to temporal variation in the dissolved organic matter pool of an agriculturally impacted stream
Ghosh, Suchismita; Ayayee, Paul A.; Leff, Laura G.
published: Aug 1, 2016
published online: Jul 5, 2016
manuscript accepted: Jun 20, 2016
manuscript received: Mar 14, 2016
ArtNo. ESP141018803000, Price: 29.00 €
Abstract Changes in biotic and abiotic variables in streams can drive shifts in microbial community composition and function. In this study, we uncovered temporal patterns in bacterial OTU richness and enzyme activities in the sediment of an agriculturally impacted stream that were driven by seasonal changes in stream discharge, nitrogen (N) availability, fractions of the dissolved organic matter (DOM) pool, and algal biomass, using molecular techniques and enzymatic assays (substrate analogues linked to fluorescent molecules). Overall, DOM composition (especially labile DOC) was strongly influenced by high algal growth in June and August, which was driven by high discharge and N availability in April and June. These factors resulted in increased bacterial abundances in both stream water and sediment in June and August. However, periods of high activities (June) of the enzymes α-glucosidase (AG), β-glucosidase (BG), N-acetylglucosaminidase (NAG) and leucine amino peptidase (LAMP) in stream sediments did not coincide with high OTU richness, since this was lowest in June. Bacterial community structure and the measured activities of these four enzymes appeared unrelated perhaps because various organisms (bacteria, fungi, algae) produce enzymes. However, enzyme changes reflect resource availability and presumably may be related to bacterial communities indirectly. Consistent with this idea, high laccase activity and OTU richness co-occurred in September and were attributed to increasing humic DOC fractions (as algal biomass decreases and labile DOC was exhausted). Overall, our results suggest that microbe-mediated nitrogen and carbon transformations by sediment microbial communities of an agriculturally impacted stream are heavily impacted by seasonal variations in biotic (algal biomass) and abiotic (discharge, N input) factors that characterize such streams.