© 2000 Heron Publishing—Victoria, Canada
Assessing forest soil CO2 efflux: an in situ comparison of four techniques
Ivan A. Janssens (1), Andrew S. Kowalski (1), Bernard Longdoz (2) and Reinhart Ceulemans (1)
1. Department of Biology, University of Antwerpen (UIA), Universiteitsplein 1, B-2610 Antwerpen, Belgium / 2. Faculté des Sciences Agronomiques de Gembloux, Physics Department, B-5030 Gembloux, Belgium / Received April 9, 1999
Summary
A dynamic, closed-chamber infrared gas analysis (IRGA) system (DC-1: CIRAS-1, PP-Systems, Hitchin, U.K.) was compared with
three other systems for measuring soil CO2 efflux: the soda lime technique (SL), the eddy correlation technique (EC), and another dynamic, closed-chamber IRGA system
(DC-2: LI-6250, Li-Cor, Inc., Lincoln, NE). Among the four systems, the DC-1 systematically gave the highest flux rates. Relative
to DC-1, SL, EC and DC-2 underestimated fluxes by 10, 36 and 46%, respectively. These large and systematic differences highlight
uncertainties in comparing fluxes from different sites obtained with different techniques.
Although the three chamber methods gave different results, the results were well correlated. The SL technique underestimated
soil CO2 fluxes compared with the DC-1 system, but both methods agreed well when the SL data were corrected for the underestimation
at higher fluxes, indicating that inter-site comparisons are possible if techniques are properly crosscalibrated. The EC was
the only system that was not well correlated with DC-1. Under low light conditions, EC values were similar to DC-1 estimates,
but under high light conditions the EC system seriously underestimated soil fluxes. This was probably because of interference
by the photosynthetic activity of a moss layer. Although below-canopy EC fluxes are not necessarily well suited for measuring
soil CO2 efflux in natural forest ecosystems, they provide valuable information about understory gas exchange when used in tandem
with soil chambers.
Keywords:
closed chamber, eddy covariance, infrared gas analysis, soda lime technique.
