Merete Bang Selsted:
Ecosystem-atmosphere exchange of carbon in a heathland under future climatic conditions

Global change is a reality. Atmospheric CO₂ levels are rising as well as mean global temperature and precipitation patterns are changing. These three environmental factors have separately and in combination effect on ecosystem processes. Terrestrial ecosystems hold large amounts of carbon, why understanding plant and soil responses to such changes are necessary, as ecosystems potentially can ameliorate or accelerate global change. To predict the feedback of ecosystems to the atmospheric CO₂ concentrations experiments imitating global change effects are therefore an important tool.

This work on ecosystem-atmosphere exchange of carbon in a heathland under future climatic conditions, shows that extended summer drought in combination with elevated temperature will ensure permanent dryer soil conditions, which decreases carbon turnover, while elevated atmospheric CO₂ concentrations will increase carbon turnover. In the full future climate scenario, carbon turnover is over all expected to increase and the heathland to become a source of atmospheric CO₂.

The methodology of static chamber CO₂ flux measurements and applying the technology in a FACE (free air CO₂ enrichment) facility is a challenge. Fluxes of CO₂ from soil to atmosphere depend on a physical equilibrium between those two medias, why it is important to keep the CO₂ gradient between soil and atmosphere unchanged during measurement. Uptake to plants via photosynthesis depends on a physiological process, which depends strongly on the atmospheric CO₂ concentration. Photosynthesis and respiration run in parallel during measurements of net ecosystem exchange, and these measurements should therefore be performed with care to both the atmospheric CO₂ concentration and the CO₂ soil-atmosphere gradient.