Measurement of CO2 evolution in situ

Summary

Soil respiration is a major flux in the global carbon cycle, and accurate measurement of soil CO2 efflux is crucial in ecosystem carbon budgets. The CO2 efflux is the result of two processes; namely the CO2 production from root and soil respiration, and the transport of CO2 to the atmosphere.
Traditionally, soil CO2 fluxes have been measured in chambers covering small patches of the soil by using either a static chamber method, where enclosures are left for 24 hr. and CO2 is collected in soda lime, or a dynamic chamber method, where enclosures are left for a shorter period (minutes) during which CO2 is registered with an infrared gas analyzer. These chamber methods have a number of disadvantages including soil disturbance while placing the chamber, temperature and moisture changes in the soil and air under the chamber, and alteration of the CO2 concentration gradient between the soil and chamber headspace. However, chamber methods are often the only methods suited to the experimental conditions with small plots where micro-meteorological methods can not be used.
Ideally, the method to be used should not affect flux rates, and their influence on microclimatic variables and concentration gradients should be minimal. Theoretically the dynamic method fulfills these criteria to a greater extent than the static method, with measurements of flux rates over relatively short periods minimizing effects on soil temperature, water content and CO2 concentration gradients. However, the dynamic method does not have the time-integrative power of the static method.
These were some of the considerations we made in relation to the three projects listed below, where in situ measurements of soil respiration are included:
(1) Soil respiration following cultivated grasslands (Eriksen & Jensen, 2001)
(2) Relationship between soil physical and microbiological parameters and degradation potentials of selected pesticides (started recently)
(3) Field CO2 and N2O fluxes in relation to prehistory of organic matter input to soil (to be started)
Results and plans from these projects will be presented.
Eriksen, J. and Jensen, L. S. (2001) Soil respiration, nitrogen mineralization and uptake in barley following cultivation of grazed grasslands. Biology and Fertility of Soils 33, 139-145.