<sup>15</sup>N enrichment as an integrator of the effects of C and N on microbial metabolism and ecosystem function

Dijkstra, Paul; LaViolette, Corinne M.; Coyle, Jeffrey S.; Doucett, Richard R.; Schwartz, Egbert; Hart, Stephen C.; Hungate, Bruce A.

doi:10.1111/j.1461-0248.2008.01154.x

Cited by 148 publications

(135 citation statements)

References 56 publications

(119 reference statements)

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“…This was further supported by low C/N and increasing enrichment of 15 N in DOM. The latter indicates a repeated microbial recycling of N in DOM, which would be in line with a strong N deficiency at the sites and an enrichment of 15 N due to higher humification (Dijkstra et al, 2008). In contrast, Kalbitz and Geyer (2002) found low δ 15 N values in highly humified DOM, but this may be explained by a varying contribution of DON supply from either the solid phase or organic matter mineralization.…”

Section: Decomposition Versus Doc Concentrations and Dom Isotopic Sigmentioning

confidence: 60%

Peat decomposition records in three pristine ombrotrophic bogs in southern Patagonia

et al. 2012

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Abstract. Ombrotrophic bogs in southern Patagonia have been examined with regard to paleoclimatic and geochemical research questions but knowledge about organic matter decomposition in these bogs is limited. Therefore, we examined peat humification with depth by Fourier Transformed Infrared (FTIR) measurements of solid peat, C/N ratio, and δ 13 C and δ 15 N isotope measurements in three bog sites. Peat decomposition generally increased with depth but distinct small scale variation occurred, reflecting fluctuations in factors controlling decomposition. C/N ratios varied mostly between 40 and 120 and were significantly correlated (R 2 > 0.55, p < 0.01) with FTIR-derived humification indices. The degree of decomposition was lowest at a site presently dominated by Sphagnum mosses. The peat was most strongly decomposed at the driest site, where currently peat-forming vegetation produced less refractory organic material, possibly due to fertilizing effects of high sea spray deposition. Decomposition of peat was also advanced near ash layers, suggesting a stimulation of decomposition by ash deposition. Values of δ 13 C were 26.5 ± 2 ‰ in the peat and partly related to decomposition indices, while δ 15 N in the peat varied around zero and did not consistently relate to any decomposition index. Concentrations of DOM partly related to C/N ratios, partly to FTIR derived indices. They were not conclusively linked to the decomposition degree of the peat. DOM was enriched in 13 C and in 15 N relative to the solid phase probably due to multiple microbial modifications and recycling of N in these N-poor environments. In summary, the depth profiles of C/N ratios, δ 13 C values, and FTIR spectra seemed to reflect changes in environmental conditions affecting decomposition, such as bog wetness, but were dominated by site specific factors, and are further influenced by ash deposition and possibly by sea spray input.

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Section: Decomposition Versus Doc Concentrations and Dom Isotopic Sigmentioning

confidence: 60%

Peat decomposition records in three pristine ombrotrophic bogs in southern Patagonia

et al. 2012

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“…with 0-4% lower d 15 N than the bulk original organic matter (Lehmann et al 2002;Dijkstra et al 2008; C. Yoshimizu, unpublished data).…”

Section: Turnover Of Nomentioning

confidence: 96%

Longitudinal distribution of nitrate δ15N and δ18O in two contrasting tropical rivers: implications for instream nitrogen cycling

et al. 2009

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The longitudinal variations in the nitrogen (d 15 N) and oxygen (d 18 O) isotopic compositions of nitrate (NO 3 -), the carbon isotopic composition (d 13 C) of dissolved inorganic carbon (DIC) and the d 13 C and d 15 N of particulate organic matter were determined in two Southeast Asian rivers contrasting in the watershed geology and land use to understand internal nitrogen cycling processes. The d 15 N NO 3 became higher longitudinally in the freshwater reach of both rivers. The d 18 O NO 3 also increased longitudinally in the river with a relatively steeper longitudinal gradient and a less cultivated watershed, while the d 18 O NO 3 gradually decreased in the other river. A simple model for the d 15 N NO 3 and the d 18 O NO 3 that accounts for simultaneous input and removal of NO 3 -suggested that the dynamics of NO 3 -in the former river were controlled by the internal production by nitrification and the removal by denitrification, whereas that in the latter river was significantly affected by the anthropogenic NO 3 -loading in addition to the denitrification and/or assimilation. In the freshwater-brackish transition zone, heterotrophic activities in the river water were apparently elevated as indicated by minimal dissolved oxygen, minimal d 13 C DIC and maximal pCO 2 . The d 15 N of suspended particulate nitrogen (PN) varied in parallel to the d 15 N NO 3 there, suggesting that the biochemical recycling processes (remineralization of PN coupled to nitrification, and assimilation of NO 3 --N back to PN) played dominant roles in the instream nitrogen transformation. In the brackish zone of both rivers, the d 15 N NO 3 displayed a declining trend while the d 18 O NO 3 increased sharply. The redox cycling of NO 3 -/NO 2 -and/or deposition of atmospheric nitrogen oxides may have been the major controlling factor for the estuarine d 15 N NO 3 and d 18 O NO 3 , however, the exact mechanism behind the observed trends is currently unresolved.

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“…As a consequence, D 15 N SMB/WSN increased significantly with time. It has been suggested that the relationship between the the 15 N enrichment of the microbial biomass relative to that of the water soluble fraction and C/N ratio of the water soluble fraction is an indicator of change in microbial N metabolism (Dijkstra et al 2008). Here, a significant linear regression (r 2 = 0.66, P \ 0.001, y = 3.35 -1.17x) was also found between C/N ratio of the water soluble fraction and D 15 N SMB/WSN .…”

Section: Changes In D 13 C and D 15 N Valuesmentioning

confidence: 99%

Variations in microbial isotopic fractionation during soil organic matter decomposition

et al. 2010

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International audiencehe soil microbial biomass (SMB) is known to participate in key soil processes such as the decomposition of soil organic matter (SOM). However, its contribution to the isotopic composition of the SOM is not clear yet. Shifts in the 13C and 15N natural abundances of the SMB and SOM fractions (mineralised, water soluble and non-extractable) were investigated by incubating an unamended arable soil for 6 months. Microbial communities were also studied using Fatty Acid Methyl Ester specific isotope analysis. The SMB was significantly 13C and 15N-enriched relative to other fractions throughout the incubation. However, significant isotopic variations with time were also observed due to the rapid consumption of relatively 13C-enriched water soluble compounds. The increase in the difference in SMB and water soluble 15N compositions as the water soluble C/N ratio decreased, indicated a shift from N assimilation to N dissimilation during the incubation. These changes also induced modifications of the microbial community structure. Once the system reached a steady-state (after 1 month), the isotopic trends appeared to corroborate those obtained in long term experiments in the field in that there was a constant microbial isotopic fractionation leading to a 13C and 15N enrichment of the SOM over the long-term. This work also suggests that caution must be exercised when interpreting short term incubation studies since perturbations associated with experimental set-up can have an important effect on C and N dynamics, microbial fractionation of 13C and 15N and microbial community structure

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¹⁵N enrichment as an integrator of the effects of C and N on microbial metabolism and ecosystem function

Cited by 148 publications

References 56 publications

Peat decomposition records in three pristine ombrotrophic bogs in southern Patagonia

Peat decomposition records in three pristine ombrotrophic bogs in southern Patagonia

Longitudinal distribution of nitrate δ15N and δ18O in two contrasting tropical rivers: implications for instream nitrogen cycling

Variations in microbial isotopic fractionation during soil organic matter decomposition

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15N enrichment as an integrator of the effects of C and N on microbial metabolism and ecosystem function

Cited by 148 publications

References 56 publications

Peat decomposition records in three pristine ombrotrophic bogs in southern Patagonia

Peat decomposition records in three pristine ombrotrophic bogs in southern Patagonia

Longitudinal distribution of nitrate δ15N and δ18O in two contrasting tropical rivers: implications for instream nitrogen cycling

Variations in microbial isotopic fractionation during soil organic matter decomposition

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¹⁵N enrichment as an integrator of the effects of C and N on microbial metabolism and ecosystem function