Interpretation and evaluation of combined measurement techniques for soil CO2
 efflux: Discrete surface chambers and continuous soil CO2
 concentration probes

Measurements of soil CO2 efflux and soil CO2 concentration concurrently are important for understanding the mechanism and regulation of CO2 in the soil. We have analysed CO2 concentration in a soil profile and soil CO2 efflux in three typical forests in subtropical China: monsoon evergreen broad-leaved forest (BF, 400 years old), pine and broad-leaved mixed forest (MF, 80 years old), and pine forest (PF, 70 years old). A portable soil CO2 sampler of simple sample operation was designed and used. The seasonal patterns of soil surface CO2 efflux and soil CO2 concentration were observed, and were positively correlated with rainfall, soil temperature, and moisture. The mean values of soil CO2 concentrations at the 15, 30, 45, and 60 cm soil depth were higher in BF (3368–9243 μL L–1) than in MF (1495–7662 μL L–1) and PF (1566–5730 μL L–1), while the mean values of soil surface CO2 efflux (Rsurface) were 0.55 ± 0.11 g m–2 h–1 in BF, 0.52 ± 0.10 g m–2 h–1 in MF, and 0.45 ± 0.07 g m–2 h–1 in PF. Soil CO2 concentration and Rsurface increased gradually with the age of the forests, but the incremental increase in soil CO2 concentration will be greater than that of Rsurface in MF and PF compared with BF. The data suggested that, although older forests have more C, younger forests probably will sequester C as CO2 faster than older forests.

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Seasonal patterns of soil CO2 efflux and soil air CO2 concentration in a Scots pine forest: comparison of two chamber techniques

Global Change Biology ◽

10.1046/j.1365-2486.2003.00588.x ◽

2003 ◽

Vol 9 (3) ◽

pp. 371-382 ◽

Cited By ~ 53

Author(s):

JUKKA PUMPANEN ◽

HANNU ILVESNIEMI ◽

MARTTI PERÄMÄKi ◽

PERTTI HARI

Keyword(s):

Scots Pine ◽

Co2 Concentration ◽

Soil Co2 Efflux ◽

Pine Forest ◽

Seasonal Patterns ◽

Co2 Efflux ◽

Soil Co2 ◽

Soil Air ◽

Scots Pine Forest

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Overestimation of closed chamber soil CO2 effluxes at low atmospheric turbulence

10.5194/bg-2016-490 ◽

2016 ◽

Cited By ~ 1

Author(s):

Andreas Brændholt ◽

Klaus Steenberg Larsen ◽

Andreas Ibrom ◽

Kim Pilegaard

Keyword(s):

Atmospheric Turbulence ◽

Abiotic Factors ◽

Measurement Techniques ◽

Negative Relationship ◽

Soil Co2 Efflux ◽

Co2 Efflux ◽

Diurnal Pattern ◽

Soil Co2 ◽

Closed Chamber ◽

Biotic And Abiotic Factors

Abstract. Soil respiration (Rs) is an important component of ecosystem carbon balance and accurate quantification of the diurnal and seasonal variation of Rs is crucial for correct interpretation of the response of Rs to biotic and abiotic factors, as well as for estimating annual soil CO2 efflux rates. In this study, we measured Rs hourly for one year by automated closed chambers in a temperate Danish beech forest. The data showed a clear diurnal pattern of Rs across all seasons with higher rates during night-time than during day-time. However, further analysis showed a clear negative relationship between flux rates and friction velocity (u∗) above the canopy, suggesting that Rs was overestimated at low atmospheric turbulence throughout the year due to non-steady state conditions during measurements. Filtering out data at low u∗ values removed or even inverted the observed diurnal pattern, such that the highest effluxes were now observed during day-time, and also led to a substantial decrease in the estimated annual soil CO2 efflux. By installing fans to produce continuous turbulent mixing of air around the soil chambers, we tested the hypothesis that overestimation of soil CO2 effluxes during low u∗ can be eliminated if proper mixing of air is ensured, and indeed the use of fans removed the overestimation of Rs rates during low u∗. Artificial turbulent air mixing may thus provide a method to overcome the problems of using closed chamber gas exchange measurement techniques during naturally occurring low atmospheric turbulence conditions. Other possible effects from using fans during soil CO2 efflux measurements are discussed. In conclusion, periods with low atmospheric turbulence may provide a significant source of error in Rs rates estimated by the use of closed chamber techniques and erroneous data must be filtered out to obtain unbiased diurnal patterns, accurate relationships to biotic and abiotic factors, and before estimating Rs fluxes over longer time scales.

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A field-based method for simultaneous measurements of the 18O and 13C soil CO2 efflux

Biogeosciences Discussions ◽

10.5194/bgd-1-1-2004 ◽

2004 ◽

Vol 1 (1) ◽

pp. 1-25 ◽

Cited By ~ 1

Author(s):

B. Mortazavi ◽

J. L. Prater ◽

J. P. Chanton

Keyword(s):

Isotopic Composition ◽

Soil Water ◽

Soil Surface ◽

Co2 Concentration ◽

Vertical Gradient ◽

Soil Co2 Efflux ◽

Co2 Efflux ◽

Soil Co2 ◽

Fractionation Factor ◽

Keeling Plots

Abstract. Three approaches for determining the stable isotopic composition (13C and 18O) of soil CO2 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 a Keeling plot to determine the 18O and 13C of CO2 emitted from the soil. These results were then compared to the 18O and 13C 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 belowground soil 18O CO2 and to CO2 in equilibrium with soil water 18O. Mini-tower 18O Keeling plots were linear and highly significant (0.81<r2<0.96), in contrast to chamber 18O Keeling plots, which showed significant curvature, necessitating the use of a mass balance to calculate the 18O of respired CO2. In the chambers, the values determined for the 18O of soil respired CO2 approached the value of CO2 in equilibrium with surficial soil water, and the results were significantly 18O enriched relative to the mini-tower results and the 18O of soil CO2 efflux determined from soil CO2. There were close agreements between the three methods for the determination of the 13C of soil efflux CO2. Results suggest that the mini-towers can be effectively used in the field for determining the 18O and the 13C of soil respired CO2.

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Overestimation of closed-chamber soil CO2 effluxes at low atmospheric turbulence

Biogeosciences ◽

10.5194/bg-14-1603-2017 ◽

2017 ◽

Vol 14 (6) ◽

pp. 1603-1616 ◽

Cited By ~ 13

Author(s):

Andreas Brændholt ◽

Klaus Steenberg Larsen ◽

Andreas Ibrom ◽

Kim Pilegaard

Keyword(s):

Atmospheric Turbulence ◽

Abiotic Factors ◽

Measurement Techniques ◽

Negative Relationship ◽

Soil Co2 Efflux ◽

Co2 Efflux ◽

Diurnal Pattern ◽

Soil Co2 ◽

Closed Chamber ◽

Biotic And Abiotic Factors

Abstract. Soil respiration (Rs) is an important component of ecosystem carbon balance, and accurate quantification of the diurnal and seasonal variation of Rs is crucial for a correct interpretation of the response of Rs to biotic and abiotic factors, as well as for estimating annual soil CO2 efflux rates. In this study, we measured Rs hourly for 1 year by automated closed chambers in a temperate Danish beech forest. The data showed a clear diurnal pattern of Rs across all seasons with higher rates during night-time than during daytime. However, further analysis showed a clear negative relationship between flux rates and friction velocity (u∗) above the canopy, suggesting that Rs was overestimated at low atmospheric turbulence throughout the year due to non-steady-state conditions during measurements. Filtering out data at low u∗ values removed or even inverted the observed diurnal pattern, such that the highest effluxes were now observed during daytime, and also led to a substantial decrease in the estimated annual soil CO2 efflux. By installing fans to produce continuous turbulent mixing of air around the soil chambers, we tested the hypothesis that overestimation of soil CO2 effluxes during low u∗ can be eliminated if proper mixing of air is ensured, and indeed the use of fans removed the overestimation of Rs rates during low u∗. Artificial turbulent air mixing may thus provide a method to overcome the problems of using closed-chamber gas-exchange measurement techniques during naturally occurring low atmospheric turbulence conditions. Other possible effects from using fans during soil CO2 efflux measurements are discussed. In conclusion, periods with low atmospheric turbulence may provide a significant source of error in Rs rates estimated by the use of closed-chamber techniques and erroneous data must be filtered out to obtain unbiased diurnal patterns, accurate relationships to biotic and abiotic factors, and before estimating Rs fluxes over longer timescales.

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