Regulation and Seasonal Dynamics of Extracellular Enzyme Activities in the Sediments of a Large Lowland River

Abstract

We tested whether seasonal changes in the sources of organic substances for microbial metabolism were reflected changes in the activities of five extracellular enzymes in the eighth order lowland River Elbe, Germany. Leucine aminopeptidase showed the highest activities in the water column and the sediments, followed by phosphatase > beta-glucosidase > alpha-glucosidase > exo-1,4-beta-glucanase. Individual enzymes exhibited characteristic seasonal dynamics, as indicated by their relative contribution to cumulative enzyme activity. Leucine aminopeptidase was significantly more active in spring and summer. In contrast, the carbohydrate-degrading enzymes peaked in autumn, and beta-glucosidase activity peaked once again in winter. Thus, in sediments, the ratio of leucine aminopeptidase/beta-glucosidase reached significant higher medians in spring and summer (5-cm depth: ratio 7.7; 20-cm depth: ratio 10.1) than in autumn and winter (5-cm depth: ratio 3.7, 20-cm depth: ratio 6.3). The relative activity of phosphatase in the sediments was seasonally related to both the biomass of planktonic algae as well as to the high content of total particulate phosphorus in autumn and winter. Due to temporal shifts in organic matter supply and changes in the storage capacity of sediments, the seasonal peaks of enzyme activities in sediments exhibited a time lag of 2-3 months compared to that in the water column, along with a significant extension of peak width. Hence, our data show that the seasonal pattern of extracellular enzyme activities provides a sensitive approach to infer seasonal or temporary availability of organic matter in rivers from autochthonous and allochthonous sources. From the dynamics of individual enzyme activities, a consistent synoptic pattern of heterotrophic functioning in the studied river ecosystem could be derived. Our data support the revised riverine productivity model predicting that the metabolism of organic matter in high-order rivers is mainly fuelled by autochthonous production occurring in these reaches and riparian inputs.

Disconnect of microbial structure and function: enzyme activities and bacterial communities in nascent stream corridors

“…Furthermore, temperature can evidently not account for the often-elevated potential activities in spring, autumn and, in one case (chitinase), in winter. This limited temperature response is consistent with data from surface water (Sinsabaugh and Follstad Shah, 2010), fine sediments (Wilczek et al, 2005) and biofilms (Jones and Lock, 1993) of lowland streams and rivers and suggests important, seasonally varying determinants of enzyme activities in addition to temperature. One such factor is light.…”

“…Microbial activities in these patches also vary over time in response to temporal variation of environmental conditions (Jones and Lock, 1993;Wilczek et al, 2005;Sinsabaugh and Follstad Shah, 2010), changes in water availability (Romaní et al, 2006a, b;Artigas et al, 2009) and varying interactions among diverse microbial groups (for example, bacteria and algae; Romaní et al, 2006a, b;Ylla et al, 2009;Pohlon et al, 2010). This creates a spatiotemporal template that provides scope for gradients in environmental conditions along hydrological flow paths from upland sites to stream channels and longitudinally in stream corridors (Larned et al, 2010).…”

Bacterial structures and ecosystem functions in glaciated floodplains: contemporary states and potential future shifts

“…Increased ester and endopeptidase activity characterized kryal sediments, whereas a-glucosidase, b-glucosidase, b-xylosidase, N-acetyl-glucosaminidase, leucine aminopeptidase and phosphatase were more expressed in krenal systems. The importance of these typical krenal enzymes has been described for lowland rivers in both the water column and sediments (Wilczek et al, 2005) and mirrors the importance of gathering carbon, nitrogen and phosphorous from different sources. For instance, krenal systems have high carbon input via cellulose, thus expressing Bet becomes important within krenal sediments to gather carbon from this non-limiting resource (Zah and Uehlinger, 2001).…”

Benthic fluxes of dissolved organic nitrogen in the lower St. Lawrence estuary and implications for selective organic matter degradation

“…The rate-determining step for both aerobic and anaerobic microbial degradation of POM and production of DOM is the hydrolysis by extracellular enzymes (Wilczek et al, 2005). Higher POM reactivity induces the production and activity of bacterial hydrolytic enzymes (Boetius and Lochte, 1994;Wilczek et al, 2005), and hydrolysis proceeds under both oxic and anoxic conditions, although not necessarily always at the same rates (Hansen and Blackburn 1991;Kristensen and Holmer, 2001). In this regard, Thibodeau et al (2010) recently reported that OM remineralization rates along the LC are highest in the lower estuary and decrease eastwards.…”