Processes controlling the oxygen isotope ratio of soil CO2: analytic and numerical modeling

Stern, Libby A.; Baisden, W. Troy; Amundson, Ronald

doi:10.1016/s0016-7037(98)00293-2

Cited by 63 publications

(64 citation statements)

References 40 publications

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“…This net rate of CO 2 production integrates the effects of respiration and of CO 2 storage and release discussed above. The one-dimensional model is summarized by the diffusion-production equation (Jury et al, 1991;Stern et al, 1999):…”

Section: Expected Relationships Between O 2 and Co 2 In Soilsmentioning

confidence: 99%

Using O2 to study the relationships between soil CO2 efflux and soil respiration

et al. 2015

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Abstract. Soil respiration is the sum of respiration processes in the soil and is a major flux in the global carbon cycle. It is usually assumed that the CO 2 efflux is equal to the soil respiration rate. Here we challenge this assumption by combining measurements of CO 2 with high-precision measurements of O 2 . These measurements were conducted on different ecosystems and soil types and included measurements of air samples taken from the soil profile of three Mediterranean sites: a temperate forest and two alpine forests. Rootfree soils from the alpine sites were also incubated in the lab. We found that the ratio between the CO 2 efflux and the O 2 influx (defined as apparent respiratory quotient, ARQ) was in the range of 0.14 to 1.23 and considerably deviated from the value of 0.9 ± 0.1 expected from the elemental composition of average plants and soil organic matter. At the Mediterranean sites, these deviations are explained as a result of CO 2 dissolution in the soil water and transformation to bicarbonate ions in these high-pH soils, as well as by carbonate mineral dissolution and precipitation processes. Thus, a correct estimate of the short-term, chamber-based biological respiratory flux in such soils can only be made by dividing the measured soil CO 2 efflux by the average (efflux-weighted) soil profile ARQ. Applying this approach to a semiarid pine forest resulted in an estimated short-term biological respiration rate that is 3.8 times higher than the chamber-measured surface CO 2 . The ARQ values often observed in the more acidic soils were unexpectedly low (< 0.7). These values probably result from the oxidation of reduced iron, which has been formed previously during times of high soil moisture and local anaerobic conditions inside soil aggregates. The results reported here provide direct quantitative evidence of a large temporal decoupling between soil-gas exchange fluxes and biological soil respiration.

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Section: Expected Relationships Between O 2 and Co 2 In Soilsmentioning

confidence: 99%

Using O2 to study the relationships between soil CO2 efflux and soil respiration

et al. 2015

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“…For our qualitative study, we could use observations from Neubert (1998) in the catchment area of Heidelberg, as well as globally resolved model data for assimilation isofluxes from Cuntz et al (2003b). However, for a quantitative apportionment of the CO 2 fluxes at a high temporal resolution, sampling of the isotopic content of precipitation, soil respiration and foliage gas exchange in the catchment area will be necessary with similarly high temporal resolution (Stern et al, 1999;Langendörfer et al, 2002). Further, isotope soil-atmosphere flux models are required to quantify the effect of this process at the measurement site.…”

Section: Quantitative Interpretation Of Continuousmentioning

confidence: 99%

First continuous measurements of δ18O-CO2 in air with a Fourier transform infrared spectrometer

et al. 2015

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Abstract. The continuous in situ measurement of δ 18 O in atmospheric CO 2 opens a new door to differentiating between CO 2 source and sink components with high temporal resolution. Continuous 13 C-CO 2 measurement systems have already been commercially available for some time, but until now, only few instruments have been able to provide a continuous measurement of the oxygen isotope ratio in CO 2 . Besides precise 13 C/ 12 C observations, the Fourier transform infrared (FTIR) spectrometer is also able to measure the 18 O / 16 O ratio in CO 2 , but the precision and accuracy of the measurements have not yet been evaluated. Here we present a first analysis of δ 18 O-CO 2 (and δ 13 C-CO 2 ) measurements with the FTIR analyser in Heidelberg. We used Allan deviation to determine the repeatability of δ 18 O-CO 2 measurements and found that it decreases from 0.25 ‰ for 10 min averages to about 0.1 ‰ after 2 h and remains at that value up to 24 h. We evaluated the measurement precision over a 10-month period (intermediate measurement precision) using daily working gas measurements and found that our spectrometer measured δ 18 O-CO 2 to better than 0.3 ‰ at a temporal resolution of less than 10 min. The compatibility of our FTIR-spectrometric measurements to isotoperatio mass-spectrometric (IRMS) measurements was determined by comparing FTIR measurements of cylinder gases and ambient air with IRMS measurements of flask samples, filled with gases of the same cylinders or collected from the same ambient air intake. Two-sample t tests revealed that, at the 0.01 significance level, the FTIR and the IRMS measurements do not differ significantly from each other and are thus compatible. We describe two weekly episodes of ambient air measurements, one in winter and one in summer, and discuss what potential insights and new challenges combined highly resolved CO 2 , δ 13 C-CO 2 and δ 18 O-CO 2 records may provide in terms of better understanding regional scale continental carbon exchange processes.

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“…18 O of CO 2 in the atmosphere through net photosynthesis [Farquhar et al, 1993;Flanagan et al, 1994;Yakir et al, 1994;Gillon and Yakir, 2000a, 2000b, and respiration by roots and heterotrophs in soils [Tans, 1998;Miller et al, 1999;Stern et al, 1999] or foliage .…”

Section: Introductionmentioning

confidence: 99%

Oxygen isotope content of CO₂ in nocturnal ecosystem respiration: 1. Observations in forests along a precipitation transect in Oregon, USA

Bowling

McDowell

Welker

et al. 2003

Global Biogeochemical Cycles

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[1] The oxygen isotope content of nocturnal ecosystem respiration (d 18 O R ) was examined in forests along a precipitation gradient in Oregon, USA, to determine whether site-to-site variation in d18 O R was more strongly related to variation in d 18O of precipitation or to evaporative processes that isotopically modify water pools within ecosystems. Measurements were made over 4 years at sites ranging in mean annual precipitation from 227 to 2760 mm. There was a gradient in the isotopic content (d 18 O) of precipitation, with inland sites receiving isotopically depleted precipitation (more negative d 18O) relative to coastal sites. The d18 O of water in plant xylem generally followed the isotopic pattern of precipitation. Inland forests were drier than coastal forests, leading to a gradient in the vapor pressure deficit of air that caused isotopic enrichment of soil and leaf water. The enriched soil and leaf water pools influenced the isotopic composition of respired CO 2 , leading to variation in observed d 18 O R at inland sites relative to those nearer the coast, indicating that fractionation due to evaporative enrichment overshadowed the original isotopic composition of precipitation as a first order control on d 18 O R .

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Processes controlling the oxygen isotope ratio of soil CO2: analytic and numerical modeling

Cited by 63 publications

References 40 publications

Using O<sub>2</sub> to study the relationships between soil CO<sub>2</sub> efflux and soil respiration

Using O<sub>2</sub> to study the relationships between soil CO<sub>2</sub> efflux and soil respiration

First continuous measurements of δ<sup>18</sup>O-CO<sub>2</sub> in air with a Fourier transform infrared spectrometer

Oxygen isotope content of CO₂ in nocturnal ecosystem respiration: 1. Observations in forests along a precipitation transect in Oregon, USA

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Processes controlling the oxygen isotope ratio of soil CO2: analytic and numerical modeling

Cited by 63 publications

References 40 publications

Using O&lt;sub&gt;2&lt;/sub&gt; to study the relationships between soil CO&lt;sub&gt;2&lt;/sub&gt; efflux and soil respiration

Using O&lt;sub&gt;2&lt;/sub&gt; to study the relationships between soil CO&lt;sub&gt;2&lt;/sub&gt; efflux and soil respiration

First continuous measurements of δ&lt;sup&gt;18&lt;/sup&gt;O-CO&lt;sub&gt;2&lt;/sub&gt; in air with a Fourier transform infrared spectrometer

Oxygen isotope content of CO2 in nocturnal ecosystem respiration: 1. Observations in forests along a precipitation transect in Oregon, USA

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Using O<sub>2</sub> to study the relationships between soil CO<sub>2</sub> efflux and soil respiration

Using O<sub>2</sub> to study the relationships between soil CO<sub>2</sub> efflux and soil respiration

First continuous measurements of δ<sup>18</sup>O-CO<sub>2</sub> in air with a Fourier transform infrared spectrometer

Oxygen isotope content of CO₂ in nocturnal ecosystem respiration: 1. Observations in forests along a precipitation transect in Oregon, USA