scholarly journals Seasonal and vertical variations in soil CO<sub>2</sub> production in a beech forest: an isotopic flux-gradient approach

2016 ◽  
Author(s):  
Emilie Delogu ◽  
Bernard Longdoz ◽  
Caroline Plain ◽  
Daniel Epron
Keyword(s):  
Isotopic Composition ◽  
Vertical Profile ◽  
Soil Layer ◽  
Co2 Production ◽  
Co2 Efflux ◽  
Soil Co2 ◽  
Soil Layers ◽  
Flux Gradient ◽  
Co2 Transport ◽  
Gradient Approach

Abstract. Soil CO2 efflux results from the transport of CO2 from several respiration sources within the soil profile. A flux – gradient approach (FGA) was used to assess the vertical profile of CO2 production (P_CO2) and its isotopic composition (δ13P_CO2) from the measurement of the vertical profile of CO2 concentration and CO2 isotopic composition combined with soil CO2 and δ13CO2 effluxes. Variations in P_CO2 and δ13P_CO2 within different soil layers were analyzed at different time scales. In the first soil layers, P_CO2 was probably underestimated and δ13P_CO2 overestimated when CO2 transport was not solely diffusive. At the seasonal scale, a vertical gradient of P_CO2 temperature sensitivity was observed. At the within-day scale, variations in soil temperature were too weak to explain the strong variations in P_CO2. At the daily time scale, δ13P_CO2 of sources located between −10 and −20 cm depth was well correlated with the canopy inherent water use efficiency (IWUE) measured the day before. The strong correlation with IWUE argues in favor of an actual connection between canopy activity and soil autotrophic production. Moreover, including SWC of the current day as a second variable improved the linear regression between δ13P_CO2 and IWUE of the previous day, together explaining 76 % of the daily fluctuations in δ13P_CO2. This highlights the actual contribution of both autotrophic and heterotrophic sources to soil P_CO2. The method used gave consistent and promising results even if we could not disentangle the respective contribution of autotrophic and heterotrophic sources to CO2 production as the differences in their isotopic composition were too small and fluctuated too much. In addition, CO2 transport by turbulent advection and dispersion will need to be considered for the top soil layer.

The effect of vertical distribution functions on CO2 efflux and production calculated with the flux gradient approach

2020 ◽  
Author(s):  
Hubert Jochheim ◽  
Stephan Wirth ◽  
Sinikka Paulus ◽  
Martin Maier ◽  
Christoph Haas ◽  
...  
Keyword(s):  
Vertical Distribution ◽  
Exponential Function ◽  
Spline Function ◽  
Soil Depth ◽  
Distribution Functions ◽  
Co2 Production ◽  
Co2 Efflux ◽  
Chamber Method ◽  
Flux Gradient ◽  
Gradient Approach

&lt;p&gt;Soil respiration is one of the most significant carbon fluxes in terrestrial ecosystems. The analyses and quantification of soil CO2 production and its influencing factors play a crucial role in the understanding of the global carbon budget.&lt;/p&gt;&lt;p&gt;To investigate CO&lt;sub&gt;2&lt;/sub&gt; efflux from terrestrial soils under field conditions, manual or automated soil chambers are the most common methods. The flux-gradient approach (FGA) as an alternative method applies Fick&amp;#8217;s law to vertical profiles of soil CO&lt;sub&gt;2&lt;/sub&gt;. The FGA uses the soil gas diffusivity to calculate vertical fluxes of soil CO&lt;sub&gt;2&lt;/sub&gt; and the CO&lt;sub&gt;2&lt;/sub&gt; efflux from soil. The vertical partitioning the production of CO&lt;sub&gt;2&lt;/sub&gt; in different soil layers can be regarded as an option and an advantage of FGA as compared to chamber methods.&lt;/p&gt;&lt;p&gt;This investigation aims at clarifying whether a spline or an exponential function is more suitable for fitting vertical distributions of measured CO&lt;sub&gt;2&lt;/sub&gt; concentrations. We compared simulation results on the CO&lt;sub&gt;2&lt;/sub&gt; efflux and the vertical distribution of CO&lt;sub&gt;2&lt;/sub&gt; production within the soil when applying an exponential function or a spline function, respectively. Soil CO&lt;sub&gt;2 &lt;/sub&gt;concentrations were measured at the soil surface and at 0, 0.1, 0.2, 0.3 and 1.0 m soil depth of a Scots pine and a European beech forest stand of the Northeast German Lowlands. Additionally, the CO&lt;sub&gt;2&lt;/sub&gt; efflux was estimated by applying the manual chamber method. The results suggest that vertical distribution function of soil CO&lt;sub&gt;2&lt;/sub&gt; affects both the calculated CO&lt;sub&gt;2&lt;/sub&gt; efflux and the production of soil CO&lt;sub&gt;2&lt;/sub&gt;. The CO&lt;sub&gt;2&lt;/sub&gt; efflux from the chamber method fits best with the CO&lt;sub&gt;2&lt;/sub&gt; efflux from spline function. We discus some effects with the application of the spline function on the calculated vertical distribution of CO&lt;sub&gt;2&lt;/sub&gt; production.&lt;/p&gt;

scholarly journals Measuring and modelling the isotopic composition of soil respiration: insights from a grassland tracer experiment

2011 ◽  
Vol 8 (5) ◽  
pp. 1333-1350 ◽  
Author(s):  
U. Gamnitzer ◽  
A. B. Moyes ◽  
D. R. Bowling ◽  
H. Schnyder
Keyword(s):  
Steady State ◽  
Isotopic Composition ◽  
Transport Model ◽  
Tracer Experiment ◽  
Atmospheric Co2 ◽  
Soil Co2 ◽  
Soil Air ◽  
Co2 Transport ◽  
Atmosphere System

Abstract. The carbon isotopic composition (δ13C) of CO2 efflux (δ13Cefflux) from soil is generally interpreted to represent the actual isotopic composition of the respiratory source (δ13CRs). However, soils contain a large CO2 pool in air-filled pores. This pool receives CO2 from belowground respiration and exchanges CO2 with the atmosphere (via diffusion and advection) and the soil liquid phase (via dissolution). Natural or artificial modification of δ13C of atmospheric CO2 (δ13Catm) or δ13CRs causes isotopic disequilibria in the soil-atmosphere system. Such disequilibria generate divergence of δ13Cefflux from δ13CRs (termed "disequilibrium effect"). Here, we use a soil CO2 transport model and data from a 13CO2/12CO2 tracer experiment to quantify the disequilibrium between δ13Cefflux and δ13CRs in ecosystem respiration. The model accounted for diffusion of CO2 in soil air, advection of soil air, dissolution of CO2 in soil water, and belowground and aboveground respiration of both 12CO2 and 13CO2 isotopologues. The tracer data were obtained in a grassland ecosystem exposed to a δ13Catm of −46.9 ‰ during daytime for 2 weeks. Nighttime δ13Cefflux from the ecosystem was estimated with three independent methods: a laboratory-based cuvette system, in-situ steady-state open chambers, and in-situ closed chambers. Earlier work has shown that the δ13Cefflux measurements of the laboratory-based and steady-state systems were consistent, and likely reflected δ13CRs. Conversely, the δ13Cefflux measured using the closed chamber technique differed from these by −11.2 ‰. Most of this disequilibrium effect (9.5 ‰) was predicted by the CO2 transport model. Isotopic disequilibria in the soil-chamber system were introduced by changing δ13Catm in the chamber headspace at the onset of the measurements. When dissolution was excluded, the simulated disequilibrium effect was only 3.6 ‰. Dissolution delayed the isotopic equilibration between soil CO2 and the atmosphere, as the storage capacity for labelled CO2 in water-filled soil pores was 18 times that of soil air. These mechanisms are potentially relevant for many studies of δ13CRs in soils and ecosystems, including FACE experiments and chamber studies in natural conditions. Isotopic disequilibria in the soil-atmosphere system may result from temporal variation in δ13CRs or diurnal changes in the mole fraction and δ13C of atmospheric CO2. Dissolution effects are most important under alkaline conditions.

scholarly journals Inversely Estimating the Vertical Profile of the Soil CO2 Production Rate in a Deciduous Broadleaf Forest Using a Particle Filtering Method

PLoS ONE ◽  
2015 ◽  
Vol 10 (3) ◽  
pp. e0119001 ◽  
Author(s):  
Gen Sakurai ◽  
Seiichiro Yonemura ◽  
Ayaka W. Kishimoto-Mo ◽  
Shohei Murayama ◽  
Toshiyuki Ohtsuka ◽  
...  
Keyword(s):  
Production Rate ◽  
Particle Filtering ◽  
Vertical Profile ◽  
Co2 Production ◽  
Soil Co2 ◽  
Broadleaf Forest ◽  
Filtering Method ◽  
Soil Co2 Production ◽  
Deciduous Broadleaf Forest

scholarly journals A field-based method for simultaneous measurements of the δ<sup>18</sup>O and δ<sup>13</sup>C of soil CO<sub>2</sub> efflux

2004 ◽  
Vol 1 (1) ◽  
pp. 1-9 ◽  
Author(s):  
B. Mortazavi ◽  
J. L. Prater ◽  
J. P. Chanton
Keyword(s):  
Isotopic Composition ◽  
Soil Water ◽  
Soil Surface ◽  
Co2 Concentration ◽  
Vertical Gradient ◽  
Co2 Efflux ◽  
Soil Co2 ◽  
Fractionation Factor ◽  
Keeling Plots ◽  
Δ18o And Δ13c

Abstract. Three approaches for determining the stable isotopic composition (δ13C and δ18O) of soil CO efflux were compared. A new technique employed mini-towers, constructed of open-topped piping, that were placed on the soil surface to collect soil-emitted CO2. Samples were collected along a vertical gradient and analyzed for CO2 concentration and isotopic composition. These data were then used to produce Keeling plots to determine the δ18O and δ13C of CO2 emitted from the soil. These results were then compared to the δ18O and δ13C of soil-respired CO2 measured with two other techniques: (1) flux chambers and (2) estimation from the application of the diffusional fractionation factor to measured values of below ground soil CO2 and to CO2 in equilibrium with soil water δ18O. Mini-tower δ18O Keeling plots were linear and highly significant (0.81< r 2 > 0.96), in contrast to chamber δ18O Keeling plots, which showed significant curvature, necessitating the use of a mass balance to calculate the δ18O of respired CO2. In the chambers, the values determined for the δ18O of soil respired CO2 approached the value of CO2 in equilibrium with surficial soil water, and the results were significantly δ18O enriched relative to the mini-tower results and the δ18O of soil CO2 efflux determined from soil CO2. There were close agreements between the three methods for the determination of the δ13C of soil efflux CO2. Results suggest that the mini-towers can be effectively used in the field for determining the δ18O and the δ13C of soil-respired CO2.

Root exclusion through trenching does not affect the isotopic composition of soil CO2 efflux

2008 ◽  
Vol 319 (1-2) ◽  
pp. 1-13 ◽  
Author(s):  
Nicolas Chemidlin Prévost-Bouré ◽  
Jérome Ngao ◽  
Daniel Berveiller ◽  
Damien Bonal ◽  
Claire Damesin ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Soil Co2 Efflux ◽  
Co2 Efflux ◽  
Soil Co2 ◽  
Root Exclusion
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