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Exoenzyme Activities (exoenzyme + activity)
Selected AbstractsExoenzyme activities as indicators of dissolved organic matter composition in the hyporheic zone of a floodplain riverFRESHWATER BIOLOGY, Issue 8 2010SANDRA M. CLINTON Summary 1. We measured the hyporheic microbial exoenzyme activities in a floodplain river to determine whether dissolved organic matter (DOM) bioavailability varied with overlying riparian vegetation patch structure or position along flowpaths. 2. Particulate organic matter (POM), dissolved organic carbon (DOC), dissolved oxygen (DO), electrical conductivity and temperature were sampled from wells in a riparian terrace on the Queets River, Washington, U.S.A. on 25 March, 15 May, 20 July and 09 October 1999. Dissolved nitrate, ammonium and soluble reactive phosphorus were also collected on 20 July and 09 October 1999. Wells were characterised by their associated overlying vegetation: bare cobble/young alder, mid-aged alder (8,20 years) and old alder/old-growth conifer (25 to >100 years). POM was analysed for the ash-free dry mass and the activities of eight exoenzymes (,-glucosidase, ,-glucosidase, , -N-acetylglucosaminidase, xylosidase, phosphatase, leucine aminopeptidase, esterase and endopeptidase) using fluorogenic substrates. 3. Exoenzyme activities in the Queets River hyporheic zone indicated the presence of an active microbial community metabolising a diverse array of organic molecules. Individual exoenzyme activity (mean ± standard error) ranged from 0.507 ± 0.1547 to 22.8 ± 5.69 ,mol MUF (g AFDM),1 h,1, was highly variable among wells and varied seasonally, with the lowest rates occurring in March. Exoenzyme activities were weakly correlated with DO, DOC and inorganic nutrient concentrations. 4. Ratios of leucine aminopeptidase : ,-glucosidase were low in March, May and October and high in July, potentially indicating a switch from polysaccharides to proteins as the dominant component of microbial metabolism. 5. Principal components analysis indicated that there were patch effects and that these effects were strongest in the summer. 6. DOM degradation patterns did not change systematically along hyporheic flowpaths but varied with overlying forest patch type in the Queets River hyporheic zone, suggesting that additional carbon inputs exist. We hypothesise that the most likely input is the downward movement of DOM from overlying riparian soils. Understanding this movement of DOM from soils to subsurface water is essential for understanding both the hyporheic metabolism and the carbon budget of streams and rivers. [source] Enhanced exoenzyme activities in sediments in the presence of deposit-feeding Chironomus riparius larvaeFRESHWATER BIOLOGY, Issue 9 2007PETER STIEFArticle first published online: 10 JUN 200 Summary 1. The combined effects of deposit-feeding, bioturbation and bioirrigation by benthic macrofauna on the enzymatic hydrolysis of organic matter were studied in microcosms. Chironomus riparius larvae (Insecta, Diptera) served as model macrofauna and stinging nettle leaves (Urtica dioica) were used as a detrital food source. 2. In the upper 10 mm of the sediment (the habitat of C. riparius larvae), the activities of several exoenzymes, the contents of several fractions of particulate organic matter (POM), and the concentrations of dissolved oxidants (O2, NO) were measured on a small scale. Fluorescent particles (luminophores) were used to quantify the vertical redistribution of particles within the same layer. 3. In control sediment, the addition of detrital food enhanced exoenzyme activities in the 0,2 mm layer only. In the presence of C. riparius larvae, exoenzyme activities increased to 10 mm depth. Further, the content of POM in the 0,2 mm layer was lower in the presence than in the absence of larvae, suggesting ingestion and subduction of the added detritus. After prolonged incubation without further food addition, exoenzyme activities returned close to background values in both treatments, whereas the vertical distribution of POM remained unchanged. 4. The overall penetration depth of O2 and NO into the sediment was greater in the presence than the absence of C. riparius, the differences being more pronounced after prolonged incubation. Locally high O2 and NO concentrations due to bioirrigation by C. riparius were measured deep in the sediment. Net downward transport of particles was observed only in the presence of C. riparius larvae and only at the beginning of the incubation. 5. I conclude that deposit-feeding and bioturbation by macrofauna can quickly remove freshly deposited POM from the sediment surface and transfer it to less oxygenated sites (i.e. animal guts and deep sediment layers). Bioirrigation also increases the availability of oxidants deep in the sediment. The oscillation of oxidant supply to POM particles by ingestion,egestion, burial and re-burial, and the intermittent bioirrigation of subsurface sediment, is probably the cause of the increased rate of organic matter hydrolysis, the rate-limiting step in mineralization. [source] Molecular investigations into a globally important carbon pool: permafrost-protected carbon in Alaskan soilsGLOBAL CHANGE BIOLOGY, Issue 9 2010M. P. WALDROP Abstract The fate of carbon (C) contained within permafrost in boreal forest environments is an important consideration for the current and future carbon cycle as soils warm in northern latitudes. Currently, little is known about the microbiology or chemistry of permafrost soils that may affect its decomposition once soils thaw. We tested the hypothesis that low microbial abundances and activities in permafrost soils limit decomposition rates compared with active layer soils. We examined active layer and permafrost soils near Fairbanks, AK, the Yukon River, and the Arctic Circle. Soils were incubated in the lab under aerobic and anaerobic conditions. Gas fluxes at ,5 and 5 °C were measured to calculate temperature response quotients (Q10). The Q10 was lower in permafrost soils (average 2.7) compared with active layer soils (average 7.5). Soil nutrients, leachable dissolved organic C (DOC) quality and quantity, and nuclear magnetic resonance spectroscopy of the soils revealed that the organic matter within permafrost soils is as labile, or even more so, than surface soils. Microbial abundances (fungi, bacteria, and subgroups: methanogens and Basidiomycetes) and exoenzyme activities involved in decomposition were lower in permafrost soils compared with active layer soils, which, together with the chemical data, supports the reduced Q10 values. CH4 fluxes were correlated with methanogen abundance and the highest CH4 production came from active layer soils. These results suggest that permafrost soils have high inherent decomposability, but low microbial abundances and activities reduce the temperature sensitivity of C fluxes. Despite these inherent limitations, however, respiration per unit soil C was higher in permafrost soils compared with active layer soils, suggesting that decomposition and heterotrophic respiration may contribute to a positive feedback to warming of this eco region. [source] Exoenzyme activities as indicators of dissolved organic matter composition in the hyporheic zone of a floodplain riverFRESHWATER BIOLOGY, Issue 8 2010SANDRA M. CLINTON Summary 1. We measured the hyporheic microbial exoenzyme activities in a floodplain river to determine whether dissolved organic matter (DOM) bioavailability varied with overlying riparian vegetation patch structure or position along flowpaths. 2. Particulate organic matter (POM), dissolved organic carbon (DOC), dissolved oxygen (DO), electrical conductivity and temperature were sampled from wells in a riparian terrace on the Queets River, Washington, U.S.A. on 25 March, 15 May, 20 July and 09 October 1999. Dissolved nitrate, ammonium and soluble reactive phosphorus were also collected on 20 July and 09 October 1999. Wells were characterised by their associated overlying vegetation: bare cobble/young alder, mid-aged alder (8,20 years) and old alder/old-growth conifer (25 to >100 years). POM was analysed for the ash-free dry mass and the activities of eight exoenzymes (,-glucosidase, ,-glucosidase, , -N-acetylglucosaminidase, xylosidase, phosphatase, leucine aminopeptidase, esterase and endopeptidase) using fluorogenic substrates. 3. Exoenzyme activities in the Queets River hyporheic zone indicated the presence of an active microbial community metabolising a diverse array of organic molecules. Individual exoenzyme activity (mean ± standard error) ranged from 0.507 ± 0.1547 to 22.8 ± 5.69 ,mol MUF (g AFDM),1 h,1, was highly variable among wells and varied seasonally, with the lowest rates occurring in March. Exoenzyme activities were weakly correlated with DO, DOC and inorganic nutrient concentrations. 4. Ratios of leucine aminopeptidase : ,-glucosidase were low in March, May and October and high in July, potentially indicating a switch from polysaccharides to proteins as the dominant component of microbial metabolism. 5. Principal components analysis indicated that there were patch effects and that these effects were strongest in the summer. 6. DOM degradation patterns did not change systematically along hyporheic flowpaths but varied with overlying forest patch type in the Queets River hyporheic zone, suggesting that additional carbon inputs exist. We hypothesise that the most likely input is the downward movement of DOM from overlying riparian soils. Understanding this movement of DOM from soils to subsurface water is essential for understanding both the hyporheic metabolism and the carbon budget of streams and rivers. [source] | ||||||||||