Nitrogen isotope fractionation in soils and microbial reactions

Delwiche, C. C.; Steyn, P. L.

doi:10.1021/es60046a004

Cited by 478 publications

(254 citation statements)

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“…Early reports on variations in '""N abundance in nature were made by, amongst others,, Schoenheimer& Rittenberg (1929), Hoering (1955), Parwel, Ryhage & Wickman (1957), Wellman, Cook & Krouse (1968) and Delwiche & Steyn (1970). It was realized that regular variations in stable N ratios could potentially provide useful, sometimes unique, information about sources of N used by plants, and fluxes of N in ecosystems.…”

Section: Discussionmentioning

confidence: 99%

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Tansley Review No. 95¹⁵N natural abundance in soil‐plant systems

1997

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summary Equilibrium and kinetic isotope fractionations during incomplete reactions result in minute differences in the ratio between the two stable X isotopes, 15N and 14N, in various N pools. In ecosystems such variations (usually expressed in per mil [δ15N] deviations from the standard atmospheric N2) depend on isotopic signatures of inputs and outputs, the input‐output balance, N transformations and their specific isotope effects, and compartmentation of N within the system. Products along a sequence of reactions, e.g. the N mineralization‐N uptake pathway, should, if fractionation factors were equal for the different reactions, become progressively depleted. However, fractionation factors van. For example, because nitrification discriminates against 15N in the substrate more than does N mineralization, NH4+can become isotopically heavier than the organic N from which it is derived. Levels of isotopic enrichment depend dynamically on the stoichiometry of reactions, as well as on specific abiotic and biotic conditions. Thus, the δ15N of a specific N pool is not a constant, and 15N of a N compound added to the system is not a conservative, unchanging tracer. This fact, together with analytical problems of measuring 15N in small and dynamic pools of N in the soil‐plant system, and the complexity of the X cycle itself (for instance the abundance of reversible reactions), limit the possibilities of making inferences based on observations of 15N abundance in one or a few pools of N in a system. Nevertheless, measurements of δ15N might offer the advantage of giving insights into the N cycle without disturbing the system by adding 15N tracer. Such attempts require, however, that the complex factors affecting 15N in plants be taken into account, viz. (i) the source(s) of N (soil, precipitation, NOX, NH3, N2‐fixation), (ii) the depth(s) in soil from which N is taken up, (iii) the form(s) of soil‐N used (organic N, NH4+, NO3−), (iv) influences of mycorrhizal symbioses and fractionations during and after N uptake by plants, and (v) interactions between these factors and plant phenology. Because of this complexity, data on δ15N can only be used alone when certain requirements are met, e.g. when a clearly discrete N source in terms of amount and isotopic signature is studied. For example, it is recommended that N in non‐N2‐fixing species should differ more than 5% from N derived by N2‐fixation, and that several non‐N2‐fixing references are used, when data on δ15N are used to estimate Na‐fixation in poorly described ecosystems. As well as giving information on N source effects, δ15N can give insights into N cycle rates. For example, high levels of N deposition onto previously N‐limited systems leads to increased nitrification, which produces 15N‐enriched NH4 and N‐depleted NO3. As many forest plants prefer NH4−they become enriched in 15N in such circumstances. This change in plant 15N will subsequently also occur in the soil surface horizon after litter‐fall, and might be a useful indicator of N saturation, especially since ...

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Section: Discussionmentioning

confidence: 99%

“…Cheng, Bremer & Edwards, 1964;Delwiche & Steyn, 1970). It has been suggested (Handley & Raven, 1992) that this is caused by the roughlyl 0 times larger isotope effect of denitrification compared w ith that of Nj-fixation (cf.…”

Section: Assessment Of N Balances Of Ecosystemsmentioning

confidence: 99%

Tansley Review No. 95¹⁵N natural abundance in soil‐plant systems

1997

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“…A number of investiators have reported a small, but measureable, difference in the 5N abundance of symbiotic N2-fixing and nonfLxing plants growing at the same site (1,2,6,7,12,15,18). The difference is always in the same direction, with the N2-fixing plant being less abundant in "N than nonfixing plants.…”

Section: Introductionmentioning

confidence: 99%

“…The isotope effect on NO3-uptake by a nonnodulating isoline of soybeans (variety Harosoy), marigold (Tagetes erecta ILl) and ryegrass (Lolium perenne ILI) was estimated from the difference between the "N abundance of the total N of plants grown hydroponically and that of NO3-supplied in the medium. It was found to be about -5%o (8 = 1.005).A number of investiators have reported a small, but measureable, difference in the 5N abundance of symbiotic N2-fixing and nonfLxing plants growing at the same site (1,2,6,7,12,15,18). The difference is always in the same direction, with the N2-fixing plant being less abundant in "N than nonfixing plants.…”

mentioning

confidence: 96%

Isotopic Fractionation Associated With Symbiotic N₂ Fixation and Uptake of NO₃⁻ by Plants

Kohl¹,

Shearer²

1980

Plant Physiol.

151

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Isotopic fractionation associated with N2 fixation and NO3-uptake by plants are relevant to the accuracy of estimates of N2 fixation based on differences in the natural abundance of "N between N2 fixing and nonfixing plants. The isotope effect on N2 fixation by soybeans (Glyine max ILI Merrill, variety Harosoy) and red clover (Trifolium pratense ILI) was determined from the difference in "N abundance between atmospheric N2 and the total N of plants grown hydroponically with N-free nutrient solution. In soybeans the isotope effect was found to be +0.98 ± 0.18%o (f? = 0.99902). In clover the isotope effect was +1.88 ± 0.14%o (( = 0.99812). The magnitude of these inverse isotope effects is small. However, they would lead to an underestimation of the amount of N2 fixed, since the N of atmospheric origin which finally appears in the plant is made richer in "5N by the inverse isotope effects than is atmospheric N2, and, to that degree, is attributed to soil-derived N in the calculation.Isotopic fractionation associated with NO3-uptake by plants does not have a critical effect on estimates of N2 fixation which are based on natural abundance of "5N since the l"N abundance of soil-derived N in plants is measured directly (Le. after the N has undergone fractionation). Nevertheless, such fractionation is of some interest from the point of view of deciding upon the most appropriate sampling time. The isotope effect on NO3-uptake by a nonnodulating isoline of soybeans (variety Harosoy), marigold (Tagetes erecta ILl) and ryegrass (Lolium perenne ILI) was estimated from the difference between the "N abundance of the total N of plants grown hydroponically and that of NO3-supplied in the medium. It was found to be about -5%o (8 = 1.005).A number of investiators have reported a small, but measureable, difference in the 5N abundance of symbiotic N2-fixing and nonfLxing plants growing at the same site (1,2,6,7,12,15,18). The difference is always in the same direction, with the N2-fixing plant being less abundant in "N than nonfixing plants. This difference has led to the suggestion (6) that the "N abundance of plants may be used as an index of the contribution of atmospheric N2 to the N economy of plants or plant communities.Such an index may be useful in estimating the contribution of symbiotic N2 fixation integrated over time despite the fact that the acetylene reduction assay (8) is considerably more sensitive in detecting the presence of symbiotic N2-fixing activity. Estimating the contribution of symbiotically fixed N2 over the lifetime of the plant or within an ecosystem poses very different problems from estimating the instantaneous rate of nitrogenase activity from the rate of acetylene reduction. Among the problems in using the 'The work reported in this paper was supported by Grant DEB 77-01869 from the National Science Foundation. 51 acetylene assay for the former purpose are (a) conversion of acetylene reduced to N2 reduced (4); (b) large environmental, diurnal and seasonal variations (8); (c) the determination...

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“…Unlike the uptake of dissolved combined nitrogen such as ammonium and nitrate, nitrogen fixation does not result in large isotope fractionation (Hoering and Ford, 1960;Delwiche and Steyn, 1970 (Estep and Vigg, 1985;Gu et al, 2006;Patoine et al, 2006). This study addressed the variation in d 15 N POM from 96 Florida lakes with a wide range in surface area, water color and biogeochemical gradients.…”

Section: Introductionmentioning

confidence: 99%

Patterns and controls of nitrogen stable isotopes of particulate organic matter in subtropical lakes

Schelske

2010

Ann. Limnol. - Int. J. Lim.

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-Nitrogen stable isotope composition (d 15 N) of particulate organic matter (POM) has been used to infer dominant nitrogen cycling processes in lakes. However, very few studies have compared the isotope variations in lakes along trophic state and other biogeochemical gradients. Here we report an analysis of d 15 N POM and selected environmental variables from 96 subtropical lakes to assess the patterns and controls of isotope variations. Results indicate that d 15 N POM values varied from x 2.8 to 13.2‰ and were not significantly correlated with total phosphorus (TP), total nitrogen (TN) and chlorophyll a (Chl a). The 15 N depletion in POM was found across the entire trophic gradient and likely reflected contributions from planktonic nitrogen fixation. The 15 N enrichment was attributed to high primary production and the contributions of anthropogenic wastes in eutrophic lakes, and the presence of microzooplankton in the water samples of the oligotrophic lakes. The d 15 N POM was negatively correlated with water color and positively correlated with pH. Because water color is indicative of light availability which affects phytoplankton growth and pH is significantly correlated with Chl a concentration in the study lakes, the close relationship between water color, pH and d 15 N POM therefore suggests primary productivity-driven isotope fractionation. Results from this study did not reveal the importance of trophic state, nitrogen concentration and surface area to the variations of d 15 N POM and points to the complex interactions of nitrogen cycling processes in lakes with diverse biogeochemical features.

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Nitrogen isotope fractionation in soils and microbial reactions

Cited by 478 publications

References 13 publications

Tansley Review No. 95¹⁵N natural abundance in soil‐plant systems

Tansley Review No. 95¹⁵N natural abundance in soil‐plant systems

Isotopic Fractionation Associated With Symbiotic N₂ Fixation and Uptake of NO₃⁻ by Plants

Patterns and controls of nitrogen stable isotopes of particulate organic matter in subtropical lakes

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Nitrogen isotope fractionation in soils and microbial reactions

Cited by 478 publications

References 13 publications

Tansley Review No. 9515N natural abundance in soil‐plant systems

Tansley Review No. 9515N natural abundance in soil‐plant systems

Isotopic Fractionation Associated With Symbiotic N2 Fixation and Uptake of NO3− by Plants

Patterns and controls of nitrogen stable isotopes of particulate organic matter in subtropical lakes

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Tansley Review No. 95¹⁵N natural abundance in soil‐plant systems

Tansley Review No. 95¹⁵N natural abundance in soil‐plant systems

Isotopic Fractionation Associated With Symbiotic N₂ Fixation and Uptake of NO₃⁻ by Plants