Uncertainties in static closed chamber measurements of the carbon isotopic ratio of soil-respired CO

Ohlsson, K. E. Anders; Singh, Balwant; Holm, Sören; Nordgren, Anders; Lövdahl, Lars; Högberg, Peter

doi:10.1016/j.soilbio.2005.03.023

Cited by 43 publications

(73 citation statements)

References 13 publications

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“…We acknowledge that step changes in environmental conditions as applied by Simonin et al (2013) and long residence times of leaf water of > 5 h as determined by Dubbert et al (2014) might be more problematic with our approach. In general, closed static chamber systems might inherently cause errors in isotope measurements as a result of nonsteady operating conditions (Ohlsson et al, 2005;Yepez et al, 2005). The observed close agreement between xylem water and transpiration d 2 H shows, however, the reliability of the set-up chosen for this study.…”

Section: And Dmentioning

confidence: 86%

High‐resolution isotope measurements resolve rapid ecohydrological dynamics at the soil–plant interface

et al. 2016

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SummaryPlants rely primarily on rainfall infiltrating their root zones -a supply that is inherently variable, and fluctuations are predicted to increase on most of the Earth's surface. Yet, interrelationships between water availability and plant use on short timescales are difficult to quantify and remain poorly understood.To overcome previous methodological limitations, we coupled high-resolution in situ observations of stable isotopes in soil and transpiration water. We applied the approach along with Bayesian mixing modeling to track the fate of 2 H-labeled rain pulses following drought through soil and plants of deciduous tree ecosystems. We resolve how rainwater infiltrates the root zones in a nonequilibrium process and show that tree species differ in their ability to quickly acquire the newly available source. Sessile oak (Quercus petraea) adjusted root uptake to vertical water availability patterns under drought, but readjustment toward the rewetted topsoil was delayed. By contrast, European beech (Fagus sylvatica) readily utilized water from all soil depths independent of water depletion, enabling faster uptake of rainwater.Our results demonstrate that species-specific plasticity and responses to water supply fluctuations on short timescales can now be identified and must be considered to predict vegetation functional dynamics and water cycling under current and future climatic conditions.

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Section: And Dmentioning

confidence: 86%

High‐resolution isotope measurements resolve rapid ecohydrological dynamics at the soil–plant interface

et al. 2016

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“…data). The experimental design, with relatively long incubation time and distribution of the sampling points to the end points of the incubation period, should have minimized the variance when estimating d 13 C of respired CO 2 (Olsson et al 2005). The bottles were analyzed for concentration and d 13 C of DIC before and after the incubation by using a headspace equilibration technique (Cole at al.…”

Section: Methodsmentioning

confidence: 99%

Respiration of allochthonous organic carbon in unproductive forest lakes determined by the Keeling plot method

Karlsson

Jansson

Jönsson

2007

Limnology & Oceanography

104

107

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We carried out short-term (2 d) experiments in nine unproductive lakes in northern Sweden in order to investigate organic carbon sources supporting lake water respiration. Surface water was incubated in gas-tight bottles in the dark, and the concentration and isotopic composition (d 13 C) of dissolved inorganic carbon (DIC) were measured at the start and end of the incubations. Keeling plot analyses revealed that the d 13 C of the respired carbon was between 228.4% and 230.6% in the lakes and that the respired carbon was mainly of allochthonous organic carbon (AlloOC) origin. The respiration of AlloOC corresponded well with metabolic imbalances indicated by negative net ecosystem production (NEP) values in the lake waters. Keeling plot analysis of DIC accumulating in the hypolimnion of two lakes during summer stratification showed d 13 C values of around 226.6% for excess DIC, implying that the accumulation of DIC was mainly derived from respiration of AlloOC. Our data provide direct evidence that net heterotrophy of these lakes is caused by input and respiration of AlloOC. We conclude that the Keeling plot method is a powerful technique that enables characterization and quantification of the organic carbon sources contributing to respiration in aquatic systems.

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“…Small changes in this data can have a significant impact on the intercept value and there have thus been a number of evaluations of the potential errors associated with the approach. Ohlsson et al [59] showed that by initially flushing the chamber with CO 2 -free air and then allowing CO 2 to accumulate, a more enriched d 13 C value was obtained than in an unflushed chamber. These authors suggested that reducing the initial [CO 2 ] had two effects: it disturbed the diffusion process and it encouraged atmospheric air to leak into the chamber due to the generation of a strong [CO 2 ] gradient.…”

Section: Closed Chambersmentioning

confidence: 99%

“…Any residual air left in the respiration chamber runs the risk of producing an artificially enriched d 13 CR S and, in this case, by reducing the chamber CO 2 content to sub-ambient levels, the factors discussed by Ohlsson et al [59] may be a further complication. In a more recent study, Mora and Raich [64] argued that, by placing a closed chamber on the soil surface and waiting for 24 h before sampling, the accumulated soil-respired CO 2 reaches a state of equilibrium with the source CO 2 .…”

Section: Closed Chambersmentioning

confidence: 99%

“…The [CO 2 ] is then allowed to gradually increase back to ambient levels, and after stabilisation the chamber gas can be sampled when the CO 2 diffusion is once again in a steady state. Ohlsson et al [59] have suggested that in closed chambers starting to make measurements from a low [CO 2 ] can encourage the ingress of atmospheric air and change the diffusion gradient. Online measurements using this system do tend to be initially enriched [46] so that in more recent work no pre-flushing was used.…”

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Challenges in measuring the δ¹³C of the soil surface CO₂ efflux

Midwood

Millard

2010

Rapid Comm Mass Spectrometry

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The d 13C of the soil surface efflux of carbon dioxide (d 13 CR S ) has emerged as a powerful tool enabling investigation of a wide range of soil processes from characterising entire ecosystem respiration to detailed compound-specific isotope studies. d 13 CR S can be used to trace assimilated carbon transfer below ground and to partition the overall surface efflux into heterotrophic and autotrophic components. Despite this wide range of applications no consensus currently exists on the most appropriate method of sampling this surface efflux of CO 2 in order to measure d 13 CR S . Here we consider and compare the methods which have been used, and examine the pitfalls. We also consider a number of analysis options, isotope ratio mass spectrometry (IRMS), tuneable diode laser spectroscopy (TDLS) and cavity ring-down laser spectroscopy (CRDS Increasing levels of atmospheric carbon dioxide (CO 2 ) and predicted climate change have intensified research efforts to better understand the global carbon (C) cycle. Within terrestrial ecosystems, soils hold substantial amounts of C and through the exchange of CO 2 with the atmosphere have the ability to act as either a C source or a sink.[1] It is this balance and how it may be influenced by future climate change and/or land use change which has been the focus of considerable debate for some time.[2-5] The net exchange of CO 2 across a landscape can be measured using a specialist technique called eddy covariance.[6] However, eddy covariance measurements do not provide any detailed information on the underlying mechanisms which drive the terrestrial C cycle, namely photosynthesis and respiration. [7] For several decades now the stable carbon isotope 13 C has been used extensively to provide a better understanding of these two processes at a range of scales. At the ecosystem scale so-called isofluxes [8] can be measured by combining micrometeorological measurements with the 13 C analysis of CO 2 within and above the plant canopy. This type of measurement allows total ecosystem respiration to be measured -a combination of both plant (stem/leaf) respiration and the respiration from soil, or efflux rate. With the contribution of soil-derived CO 2 being important as this can provide information on the longterm overall net C balance of the system. Two basic processes contribute to the soil surface CO 2 efflux rate (R S ): autotrophic respiration from roots and the rhizosphere, and heterotrophic respiration from the turnover of soil organic matter (SOM).Against this background, measuring the rate at which CO 2 leaves the soil surface coupled with the measurement of its 13 C/ 12 C ratio (d 13 CR S ) has emerged as a key tool in ecophysiological research and global terrestrial C cycle studies. Isotopic analyses provide a means of distinguishing the C sources which contribute to this overall flux, allowing either the autotrophic or the heterotrophic components to be quantified. For example, d13 CR S measurements have been used to assess the speed at which assimilated C is transfe...

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Uncertainties in static closed chamber measurements of the carbon isotopic ratio of soil-respired CO

Cited by 43 publications

References 13 publications

High‐resolution isotope measurements resolve rapid ecohydrological dynamics at the soil–plant interface

High‐resolution isotope measurements resolve rapid ecohydrological dynamics at the soil–plant interface

Respiration of allochthonous organic carbon in unproductive forest lakes determined by the Keeling plot method

Challenges in measuring the δ¹³C of the soil surface CO₂ efflux

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Uncertainties in static closed chamber measurements of the carbon isotopic ratio of soil-respired CO

Cited by 43 publications

References 13 publications

High‐resolution isotope measurements resolve rapid ecohydrological dynamics at the soil–plant interface

High‐resolution isotope measurements resolve rapid ecohydrological dynamics at the soil–plant interface

Respiration of allochthonous organic carbon in unproductive forest lakes determined by the Keeling plot method

Challenges in measuring the δ13C of the soil surface CO2 efflux

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Challenges in measuring the δ¹³C of the soil surface CO₂ efflux