The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Jack A Gilbert - One of the best experts on this subject based on the ideXlab platform.
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salinity is a key factor driving the Nitrogen Cycling in the mangrove sediment
Science of The Total Environment, 2018Co-Authors: Haitao Wang, Yongguan Zhu, Jack A Gilbert, Xiaoru YangAbstract:Coastal ecosystems are hotspots for Nitrogen Cycling, and specifically for Nitrogen removal from water and sediment through the coupled nitrification-denitrification process. Salinity is globally important in structuring bacterial and archaeal communities, but the association between salinity and microbially-mediated nitrification and denitrification remains unclear. The denitrification activity and composition and structure of microbial nitrifiers and denitrifiers were characterized across a gradient of manipulated salinity (0, 10, 20 and 30ppt) in a mangrove sediment. Salinity negatively correlated with both denitrifying activity and the abundance of nirK and nosZ denitrifying genes. Ammonia-oxidizing bacteria (AOB), which dominated nitrification, had significantly greater abundance at intermediate salinity (10 and 20ppt). However, a positive correlation between ammonia concentration and salinity suggested that nitrifying activity might also be inhibited at higher salinity. The community structure of ammonia-oxidizing archaea (AOA) and bacteria (AOB), as well as nirK, nirS and nosZ denitrifying communities, were all significantly correlated with salinity. These changes were also associated with structural shifts in phylogeny. These findings provide a strong evidence that salinity is a key factor that influences the Nitrogen transformations in coastal wetlands, indicating that salinity intrusion caused by climate change might have a broader impact on the coastal biospheres.
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the microbial Nitrogen Cycling potential is impacted by polyaromatic hydrocarbon pollution of marine sediments
Frontiers in Microbiology, 2014Co-Authors: Jack A Gilbert, Nicole M Scott, Matthias Hess, Nicholas J Bouskill, Olivia U Mason, Janet K JanssonAbstract:During hydrocarbon exposure, the composition and functional dynamics of marine microbial communities are altered, favoring bacteria that can utilize this rich carbon source. Initial exposure of high levels of hydrocarbons in aerobic surface sediments can enrich growth of heterotrophic microorganisms having hydrocarbon degradation capacity. As a result, there can be a localized reduction in oxygen potential within the surface layer of marine sediments causing anaerobic zones. We hypothesized that increasing exposure to elevated hydrocarbon concentrations would positively correlate with an increase in denitrification processes and the net accumulation of diNitrogen. This hypothesis was tested by comparing the relative abundance of genes associated with Nitrogen metabolism and Nitrogen Cycling identified in 6 metagenomes from sediments contaminated by polyaromatic hydrocarbons from the Deepwater Horizon (DWH) oil spill in the Gulf of Mexico, and 3 metagenomes from sediments associated with natural oil seeps in the Santa Barbara Channel. An additional 8 metagenomes from uncontaminated sediments from the Gulf of Mexico were analyzed for comparison. We predicted relative changes in metabolite turnover as a function of the differential microbial gene abundances, which showed predicted accumulation of metabolites associated with denitrification processes, including anammox, in the contaminated samples compared to uncontaminated sediments, with the magnitude of this change being positively correlated to the hydrocarbon concentration and exposure duration. These data highlight the potential impact of hydrocarbon inputs on N Cycling processes in marine sediments and provide information relevant for system scale models of Nitrogen metabolism in affected ecosystems.
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impacts of bioturbation on temporal variation in bacterial and archaeal Nitrogen Cycling gene abundance in coastal sediments
Environmental Microbiology Reports, 2014Co-Authors: Bonnie Laverock, Karen Tait, Jack A Gilbert, A M Osborn, Stephen WiddicombeAbstract:In marine environments, macrofauna living in or on the sediment surface may alter the structure, diversity and function of benthic microbial communities. In particular, microbial Nitrogen (N)-Cycling processes may be enhanced by the activity of large bioturbating organisms. Here, we study the effect of the burrowing mud shrimp Upogebia deltaura upon temporal variation in the abundance of genes representing key N-Cycling functional guilds. The abundance of bacterial genes representing different N-Cycling guilds displayed different temporal patterns in burrow sediments in comparison with surface sediments, suggesting that the burrow provides a unique environment where bacterial gene abundances are influenced directly by macrofaunal activity. In contrast, the abundances of archaeal ammonia oxidizers varied temporally but were not affected by bioturbation, indicating differential responses between bacterial and archaeal ammonia oxidizers to environmental physicochemical controls. This study highlights the importance of bioturbation as a control over the temporal variation in Nitrogen-Cycling microbial community dynamics within coastal sediments.
Gilles Pinay - One of the best experts on this subject based on the ideXlab platform.
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water table elevation controls on soil Nitrogen Cycling in riparian wetlands along a european climatic gradient
Biogeochemistry, 2004Co-Authors: Mariet M Hefting, Jeanchristophe Clement, David Dowrick, Anneclaude Cosandey, Susana Bernal, C Cimpian, Andrzej Tatur, T P Burt, Gilles PinayAbstract:Riparian zones have long been considered as nitrate sinks in landscapes. Yet, riparian zones are also known to be very productive ecosystems with a high rate of Nitrogen Cycling. A key factor regulating processes in the N cycle in these zones is groundwater table fluctuation, which controls aerobic/anaerobic conditions in the soil. Nitrification and denitrification, key processes regulating plant productivity and Nitrogen buffering capacities are strictly aerobic and anaerobic processes, respectively. In this study we compared the effects of these factors on the Nitrogen Cycling in riparian zones under different climatic conditions and N loading at the European scale. No significant differences in nitrification and denitrification rates were found either between climatic regions or between vegetation types. On the other hand, water table elevation turned out to be the prime determinant of the N dynamics and its end product. Three consistent water table thresholds were identified. In sites where the water table level is within −10 cm of the soil surface, ammonification is the main process and ammonium accumulates in the topsoils. Average water tables between −10 and −30 cm favour denitrification and therefore reduce the Nitrogen availability in soils. In drier sites, that is, water table level below −30 cm, nitrate accumulates as a result of high net nitrification. At these latter sites, denitrification only occurs in fine textured soils probably triggered by rainfall events. Such a threshold could be used to provide a proxy to translate the consequences of stream flow regime change to Nitrogen Cycling in riparian zones and consequently, to potential changes in Nitrogen mitigation.
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Water table elevation controls on soil Nitrogen Cycling in riparian wetlands along a European climatic gradient
Biogeochemistry, 2003Co-Authors: Mariet M Hefting, Jeanchristophe Clement, David Dowrick, Anneclaude Cosandey, Susana Bernal, C Cimpian, Andrzej Tatur, T P Burt, Gilles PinayAbstract:Riparian zones have long been considered as nitrate sinks in landscapes. Yet, riparian zones are also known to be very productive ecosystems with a high rate of Nitrogen Cycling. A key factor regulating processes in the N cycle in these zones is groundwater table fluctuation, which controls aerobic/anaerobic conditions in the soil. Nitrification and denitrification, key processes regulating plant productivity and Nitrogen buffering capacities are strictly aerobic and anaerobic processes, respectively. In this study we compared the effects of these factors on the Nitrogen Cycling in riparian zones under different climatic conditions and N loading at the European scale. No significant differences in nitrification and denitrification rates were found either between climatic regions or between vegetation types. On the other hand, water table elevation turned out to be the prime determinant of the N dynamics and its end product. Three consistent water table thresholds were identified. In sites where the water table level is within -10 cm of the soil surface, ammonification is the main process and ammonium accumulates in the topsoils. Average water tables between -10 and -30 cm favour denitrification and therefore reduce the Nitrogen availability in soils. In drier sites, that is, water table level below -30 cm, nitrate accumulates as a result of high net nitrification. At these latter sites, denitrification only occurs in fine textured soils probably triggered by rainfall events. Such a threshold could be used to provide a proxy to translate the consequences of stream flow regime change to Nitrogen Cycling in riparian zones and consequently, to potential changes in Nitrogen mitigation.
Bonnie Laverock - One of the best experts on this subject based on the ideXlab platform.
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impacts of bioturbation on temporal variation in bacterial and archaeal Nitrogen Cycling gene abundance in coastal sediments
Environmental Microbiology Reports, 2014Co-Authors: Bonnie Laverock, Karen Tait, Jack A Gilbert, A M Osborn, Stephen WiddicombeAbstract:In marine environments, macrofauna living in or on the sediment surface may alter the structure, diversity and function of benthic microbial communities. In particular, microbial Nitrogen (N)-Cycling processes may be enhanced by the activity of large bioturbating organisms. Here, we study the effect of the burrowing mud shrimp Upogebia deltaura upon temporal variation in the abundance of genes representing key N-Cycling functional guilds. The abundance of bacterial genes representing different N-Cycling guilds displayed different temporal patterns in burrow sediments in comparison with surface sediments, suggesting that the burrow provides a unique environment where bacterial gene abundances are influenced directly by macrofaunal activity. In contrast, the abundances of archaeal ammonia oxidizers varied temporally but were not affected by bioturbation, indicating differential responses between bacterial and archaeal ammonia oxidizers to environmental physicochemical controls. This study highlights the importance of bioturbation as a control over the temporal variation in Nitrogen-Cycling microbial community dynamics within coastal sediments.
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Bioturbation: impact on the marine Nitrogen cycle
Biochemical Society Transactions, 2011Co-Authors: Bonnie Laverock, Jack a. Gilbert, A. mark Osborn, Karen Tait, Steve WiddicombeAbstract:Sediments play a key role in the marine Nitrogen cycle and can act either as a source or a sink of biologically available (fixed) Nitrogen. This Cycling is driven by a number of microbial remineralization reactions, many of which occur across the oxic/anoxic interface near the sediment surface. The presence and activity of large burrowing macrofauna (bioturbators) in the sediment can significantly affect these microbial processes by altering the physicochemical properties of the sediment. For example, the building and irrigation of burrows by bioturbators introduces fresh oxygenated water into deeper sediment layers and allows the exchange of solutes between the sediment and water column. Burrows can effectively extend the oxic/anoxic interface into deeper sediment layers, thus providing a unique environment for Nitrogen-Cycling microbial communities. Recent studies have shown that the abundance and diversity of micro-organisms can be far greater in burrow wall sediment than in the surrounding surface or subsurface sediment; meanwhile, bioturbated sediment supports higher rates of coupled nitrification-denitrification reactions and increased fluxes of ammonium to the water column. In the present paper we discuss the potential for bioturbation to significantly affect marine Nitrogen Cycling, as well as the molecular techniques used to study microbial Nitrogen Cycling communities and directions for future study.
Mariet M Hefting - One of the best experts on this subject based on the ideXlab platform.
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water table elevation controls on soil Nitrogen Cycling in riparian wetlands along a european climatic gradient
Biogeochemistry, 2004Co-Authors: Mariet M Hefting, Jeanchristophe Clement, David Dowrick, Anneclaude Cosandey, Susana Bernal, C Cimpian, Andrzej Tatur, T P Burt, Gilles PinayAbstract:Riparian zones have long been considered as nitrate sinks in landscapes. Yet, riparian zones are also known to be very productive ecosystems with a high rate of Nitrogen Cycling. A key factor regulating processes in the N cycle in these zones is groundwater table fluctuation, which controls aerobic/anaerobic conditions in the soil. Nitrification and denitrification, key processes regulating plant productivity and Nitrogen buffering capacities are strictly aerobic and anaerobic processes, respectively. In this study we compared the effects of these factors on the Nitrogen Cycling in riparian zones under different climatic conditions and N loading at the European scale. No significant differences in nitrification and denitrification rates were found either between climatic regions or between vegetation types. On the other hand, water table elevation turned out to be the prime determinant of the N dynamics and its end product. Three consistent water table thresholds were identified. In sites where the water table level is within −10 cm of the soil surface, ammonification is the main process and ammonium accumulates in the topsoils. Average water tables between −10 and −30 cm favour denitrification and therefore reduce the Nitrogen availability in soils. In drier sites, that is, water table level below −30 cm, nitrate accumulates as a result of high net nitrification. At these latter sites, denitrification only occurs in fine textured soils probably triggered by rainfall events. Such a threshold could be used to provide a proxy to translate the consequences of stream flow regime change to Nitrogen Cycling in riparian zones and consequently, to potential changes in Nitrogen mitigation.
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Water table elevation controls on soil Nitrogen Cycling in riparian wetlands along a European climatic gradient
Biogeochemistry, 2003Co-Authors: Mariet M Hefting, Jeanchristophe Clement, David Dowrick, Anneclaude Cosandey, Susana Bernal, C Cimpian, Andrzej Tatur, T P Burt, Gilles PinayAbstract:Riparian zones have long been considered as nitrate sinks in landscapes. Yet, riparian zones are also known to be very productive ecosystems with a high rate of Nitrogen Cycling. A key factor regulating processes in the N cycle in these zones is groundwater table fluctuation, which controls aerobic/anaerobic conditions in the soil. Nitrification and denitrification, key processes regulating plant productivity and Nitrogen buffering capacities are strictly aerobic and anaerobic processes, respectively. In this study we compared the effects of these factors on the Nitrogen Cycling in riparian zones under different climatic conditions and N loading at the European scale. No significant differences in nitrification and denitrification rates were found either between climatic regions or between vegetation types. On the other hand, water table elevation turned out to be the prime determinant of the N dynamics and its end product. Three consistent water table thresholds were identified. In sites where the water table level is within -10 cm of the soil surface, ammonification is the main process and ammonium accumulates in the topsoils. Average water tables between -10 and -30 cm favour denitrification and therefore reduce the Nitrogen availability in soils. In drier sites, that is, water table level below -30 cm, nitrate accumulates as a result of high net nitrification. At these latter sites, denitrification only occurs in fine textured soils probably triggered by rainfall events. Such a threshold could be used to provide a proxy to translate the consequences of stream flow regime change to Nitrogen Cycling in riparian zones and consequently, to potential changes in Nitrogen mitigation.
John D. Aber - One of the best experts on this subject based on the ideXlab platform.
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regional variation in foliar chemistry and n Cycling among forests of diverse history and composition
Ecology, 2002Co-Authors: Scott V Ollinger, Christine L Goodale, Marielouise Smith, Mary E Martin, Richard A Hallett, John D. AberAbstract:Although understanding of Nitrogen Cycling and nitrification in forest ecosystems has improved greatly over the past several decades, our ability to characterize spatial patterns is still quite limited. A number of studies have shown linkages between canopy chemistry and N Cycling, but few have considered the degree to which these trends can provide an indicator of forest N status across large, heterogeneous landscapes. In this study, we examined relationships among canopy chemistry, Nitrogen Cycling, and soil carbon:Nitrogen ratios across 30 forested stands in the White Mountains of New Hampshire. Plots included a range of species (sugar maple, red maple, American beech, yellow birch, paper birch, red spruce, balsam fir, eastern hemlock) and were broadly grouped into two disturbance categories: those that were historically affected by intensive logging and/or fire and those that experienced minimal human disturbance. Across all plots, rates of net N mineralization and net nitrification were correlated wi...
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the long term effects of land use history on Nitrogen Cycling in northern hardwood forests
Ecological Applications, 2001Co-Authors: Christine L Goodale, John D. AberAbstract:Nearly all northeastern U.S. forests have been disturbed by wind, logging, fire, or agriculture over the past several centuries. These disturbances may have long-term impacts on forest carbon and Nitrogen Cycling, affecting forests' vulnerability to N saturation and their future capacity to store C. We evaluated the long-term (80–110 yr) effects of logging and fire on aboveground biomass, foliar N (%), soil C and N pools, net N mineralization and nitrification, and NO3− leaching in northern hardwood forests in the White Mountain National Forest, New Hampshire. Historical land-use maps were used to identify five areas each containing previously logged, burned, and relatively undisturbed (old-growth) forests. Aboveground biomass averaged 192 Mg/ha on the historically disturbed sites and 261 Mg/ha on the old-growth sites, and species dominance shifted from early- successional and mid-successional species (Betula papyrifera and Acer rubrum) to late-successional species (Fagus grandifolia and particularly A. s...
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Nitrogen Cycling and Nitrogen saturation in temperate forest ecosystems.
Trends in ecology & evolution, 1992Co-Authors: John D. AberAbstract:Abstract The last decade has seen a dramatic shift in the focus of Nitrogen Cycling research in forest ecosystems. Concerns over Nitrogen deficiencies and effects of removal in harvest have given way to concerns over excess Nitrogen availability and the potential for forest decline and surface water pollution. Driving this paradigm shift is the increase in atmospheric deposition of Nitrogen to forests due to industrial and agricultural activity. At the core of the new paradigm is the concept of ‘Nitrogen saturation' of forest ecosystems. The purpose of this review is to synthesize recent advances in research relating to Nitrogen deposition effects on temperate zone forest ecosystems, and the further effects of Nitrogen saturation on environmental quality.