Soil respiration is studied on both croplands (Lonzée, Longs Tours and Bordia) and forests (Vielsalm).

Crop sites (Lonzée Terrestrial Observatory)

In agricultural ecosystems, the influences of environmental variables (temperature, soil water content, rain events,…) and crop management on soil respiration are studied, respectively, at the Lonzée and Bordia + Longs Tours sites. To assess the response of soil respiration to environmental drivers with a good temporal resolution, an experimental set-up composed of automated soil chambers (dynamic closed chamber system, Fig. 1) and usual meteorological instruments was implemented at the Lonzée site, both in cultivated areas and in root exclusion zones, so as to separate out the two components of soil respiration. The measurement frequency is half-hourly. These measurements allowed partitioning of Total Ecosystem Respiration between its heterotrophic, aerial autotrophic and below ground autotrophic components (Suleau et al., 2011).
Figure 1 – Automated soil CO2 flux measurements in a winter wheat crop at the Lonzée site.
The specific question of soil organic matter loss, associated to the process of soil heterotrophic respiration, was also specifically investigated at the Longs Tours (owned by the Walloon Agricultural Centre, Fig. 2) and Bordia (in collaboration with Unit of Crop science, Solrésidus project). At the Long Tours site, soil respiration was compared on soil plots submitted to similar pedoclimatic conditions but to different fertilisation procedures, since more than 50 years (Buysse et al., 2011).
Figure 2 – Manual soil CO2 flux measurements in root exclusion zones at the Longs Tours site.
Complementary to field investigations, a laboratory experiment was carried out with Lonzée soil samples to better understand the short-term temperature impact on soil heterotrophic respiration. Three incubators were built (Fig. 3) and the samples were incubated at three different pre-incubation temperatures, before the temperature was increased and decreased to perform daily temperature cycles between 5 and 35 °C. The CO2 fluxes were measured on the samples after each temperature change, using a dynamic closed chamber system. The experiment highlighted very different impacts of temperature at short and longer terms

[(Buysse et al., under revision) : short-term temperature impact on soil heterotrophic respiration in limed agricultural soil samples].
Figure 3 – View of the incubators used in the lab experiment designed to study the short-term soil respiration response to temperature.
Forest site

At the Vielsalm forest site, a specific experimental device was set up, in collaboration with INRA Nancy and University of Freiburg, in order to focus on the two mechanisms behind soil CO2 efflux (production and transport). Several porous tubes, which are connected to a gas analyser, were inserted at different soil depths (from 0 to 80 cm) allowing continuous soil CO2 concentration profile measurements. Soil water content and temperature probes were also inserted at each depth. In addition, automated soil chamber measurements are performed (Figure 4).
Figure 4: Experimental device for the soil CO2 efflux studies in Vielsalm.
The data from that experimental device are used to develop a model describing the CO2 transport in the soil and allowing the determination of the vertical CO2 source distribution (Figure 5) (Goffin et al., 2011).
Figure 5: Scheme of the modeling methodology.
Furthermore, the isotopic composition of soil CO2 concentration profiles and of CO2 efflux was measured. These isotopic measurements are expected to bring more information about the CO2 sources involved and the time lag between the C assimilation in the leaf and its transport to the soil as soil C substrate.

measurements, panel with the data logger and the gas analyzers, sonic anemometer; below from left to right : automated soil chambers, temperature and SWC probes, pits between which the porous tubes are located)”] Figure 6: Pictures of instruments installed in Vielsalm (above from left to right: tubes for [CO2
Contact persons:

Soil respiration modeling at the Vielsalm site: S. Goffin

Soil respiration response to temperature (lab exp.): P. Buysse

Soil respiration measurements at the Lonzée site: C. Moureaux and D. Dufranne

Residue and crop management impacts on soil respiration: D. Dufranne and P. Buysse