δ15N as an integrator of the nitrogen cycle

Robinson, David

doi:10.1016/s0169-5347(00)02098-x

Cited by 1,173 publications

(1,040 citation statements)

References 38 publications

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“…4a by coupling our steady-state model results to a semiquantitative estimate of nitrate d 15 N, comprising fractionations from assimilatory nitrate reduction, nitrification and denitrification (but neglecting fixation). The d 15 N of kerogen in sediments is assumed to reflect the isotopic composition of the nitrate with which the organic matter was in contact 27 -thus a water column influenced by high rates of denitrification will produce kerogen with a positive ( 15 N-enriched) d 15 N signal. A crucial prediction of the N-cycle feedback control that we hypothesize here is that if any such positive d 15 N signal diagnostic of denitrification is found after a systematic examination of Proterozoic sediments, it will be decoupled in time and space from the pyritization of reactive Fe.…”

Section: Resultsmentioning

confidence: 99%

Nitrogen cycle feedbacks as a control on euxinia in the mid-Proterozoic ocean

et al. 2013

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Geochemical evidence invokes anoxic deep oceans until the terminal Neoproterozoic B0.55 Ma, despite oxygenation of Earth's atmosphere nearly 2 Gyr earlier. Marine sediments from the intervening period suggest predominantly ferruginous (anoxic Fe(II)-rich) waters, interspersed with euxinia (anoxic H 2 S-rich conditions) along productive continental margins. Today, sustained biotic H 2 S production requires NO 3 À depletion because denitrifiers outcompete sulphate reducers. Thus, euxinia is rare, only occurring concurrently with (steady state) organic carbon availability when N 2 -fixers dominate the production in the photic zone.Here we use a simple box model of a generic Proterozoic coastal upwelling zone to show how these feedbacks caused the mid-Proterozoic ocean to exhibit a spatial/temporal separation between two states: photic zone NO 3 À with denitrification in lower anoxic waters, and N 2 -fixation-driven production overlying euxinia. Interchange between these states likely explains the varying H 2 S concentration implied by existing data, which persisted until the Neoproterozoic oxygenation event gave rise to modern marine biogeochemistry.

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Section: Resultsmentioning

confidence: 99%

Nitrogen cycle feedbacks as a control on euxinia in the mid-Proterozoic ocean

et al. 2013

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“…The d 15 N signature was calculated using the isotope ratio of each sample (R sample = 15 N/ 14 N) and recalculated as 15 N atom%. The incorporation of tracer-derived N into soil, shoots, and roots was estimated by an isotope mixing model (Robinson 2001). To avoid confusion, we used the terms tracer-N-uptake (N upt ) for plant N pools and tracer-N incorporation (N inc ) for the soil N pool: Figure 1.…”

Section: N Analysis and Calculationsmentioning

confidence: 99%

Nitrogen Uptake in an Alpine Kobresia Pasture on the Tibetan Plateau: Localization by 15N Labeling and Implications for a Vulnerable Ecosystem

et al. 2015

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Grasslands are very important regionally and globally because they store large amounts of carbon (C) and nitrogen (N) and provide food for grazing animals. Intensive degradation of alpine grasslands in recent decades has mainly impacted the upper root-mat/soil horizon, with severe consequences for nutrient uptake in these nutrient-limited ecosystems. We used 15 N labeling to identify the role of individual soil layers for N-uptake by Kobresia pygmaea-the dominating plant in the degraded Tibetan pasture ecosystems. We hypothesized a very efficient N-uptake corresponding mainly to the vertical distribution of living roots (topsoil > subsoil). We assume that K. pygmaea develops a very dense root-mat, which has to be maintained by small aboveground biomass, to enable this efficient N-uptake. Consequently, a higher N-investment into roots compared to shoots was hypothesized. The 15 N recovery in whole plants ($70%) indicated very efficient N-uptake from the upper injection depths (0-5 cm). The highest 15 N amounts were recovered in root biomass, whereby 15 N recovery in roots strongly decreased with depth. In contrast, 15 N recovery in shoots was generally low ($18%) and independent of the 15 N injection depth. This clearly shows that the low N demand of Kobresia shoots can be easily covered by N-uptake from any depth. Less living root biomass in lower versus upper soil was compensated by a higher specific activity of roots for N-uptake. The 15 N allocation into roots was on average 1.7 times higher than that into shoots, which agreed well with the very high R/S ratio. Increasing root biomass is an efficient strategy of K. pygmaea to compete for belowground resources at depths and periods with available resources. This implies high C-costs to maintain root biomass ($6.0 kg DM m -2 ), which must be covered by a very low amount of photosynthetically active shoots (0.3 kg DM m -2 ). It also suggests that Kobresia grasslands react extremely

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“…Plant and soil δ 15 N is a basic and powerful tool in environmental sciences and N-cycling studies (Handley and Scrimgeour 1997;Robinson 2001). Soil δ 15 N values reflect the net effect of biotic and abiotic environment on N-cycling processes (Dawson et al 2002).…”

Section: Introductionmentioning

confidence: 99%

Effects of climate, tree age, dominance and growth on δ15N in young pinewoods

Couto-Vázquez

González-Prieto

2010

Trees

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. Effects of climate, tree age, dominance and growth on δ 15 N in young pinewoods. Trees 24, 507-510. AbstractNeedles, annual rings from basal stem disks and bark of 3 dominant and 3 suppressed Pinus pinaster from a 12-year-old pine stand (naturally regenerated after a wildfire) were analysed to study the effects of climate, tree age, dominance and growth on tree δ 15 N. Foliar-N concentration in dominant pines (0.780-1.474 % N) suggested that soil N availability was sufficient, a circumstance that allowed isotopic discrimination by plants and (greater) differences in δ 15 N among trees. The δ 15 N decreases in the order wood (-0.20 to +6.12 ‰), bark (-1.84 to +1.85 ‰) and needles (-2.13 to +0.77 ‰). In all trees, before dominance establishment (years 1-8), the N stored in each ring displayed a decreasing δ 15 N tendency as the tree grows, which is mainly due to a more "closed" N cycle or an increasing importance of N sources with lower δ 15 N. After dominance establishment (years 9-12), wood δ 15 N values were higher in suppressed than in dominant trees (2.62‰ and 1.46‰, respectively; P< 0.01) while the reverse was true for needles and bark; simultaneously, the absolute amount of N stored by suppressed pines in successive rings decreased, suggesting a lower soil N assimilation. These results could be explained by lignification acting as major N source for needles in suppressed pines because products released and reallocated during lignification are 15 N-depleted compared to the source.According to principal component analysis, wood δ 15 N appears associated with wood N concentration and precipitation during the growing season, but clearly opposed to age, basal area increment and mean temperature in spring and summer.

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δ15N as an integrator of the nitrogen cycle

Cited by 1,173 publications

References 38 publications

Nitrogen cycle feedbacks as a control on euxinia in the mid-Proterozoic ocean

Nitrogen cycle feedbacks as a control on euxinia in the mid-Proterozoic ocean

Nitrogen Uptake in an Alpine Kobresia Pasture on the Tibetan Plateau: Localization by 15N Labeling and Implications for a Vulnerable Ecosystem

Effects of climate, tree age, dominance and growth on δ15N in young pinewoods

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