PARENT SESSION
Organized Oral Session 52: Casting light on nocturnal stomatal and canopy conductance
Organizer(s): NG Phillips and M Barbour
Friday, August 12, 8:00 AM - 11:30 AM, Meeting Room 510a, Level 5, Palais des congrès de Montréal

Challenges to estimating nocturnal CO₂ fluxes in terrestrial ecosystems using micrometeorological, ecophysiological and modelling techniques.

Wohlfahrt, Georg^*,1, Bahn, Michael¹, Haslwanter, Alois¹, Drösler, Matthias^{2, 3}, Cernusca, Alexander¹, ¹ University of Innsbruck, Innsbruck, Austria² Technische Universität München, München, Germany³ Universität Bayreuth, Bayreuth, Germany

ABSTRACT- In order to obtain defensible estimates of daily and longer-term net ecosystem CO₂ exchange by means of micrometeorological techniques, reliable estimates of nighttime ecosystem respiration are required. To this end we have quantified ecosystem respiration of a mountain meadow in the Austrian Alps by constraining nighttime eddy covariance measurements with ecosystem respiration derived from i) daytime eddy covariance, ii) ecosystem chamber and iii) scaled up leaf and soil chamber measurements. The study showed that the widely used discrimination of valid nighttime eddy covariance measurements based on friction velocity (u_*) is very sensitive to the imposed quality control criteria. Seasonal (8th March-28th November 2002) nighttime carbon balances simulated based on the parameters derived from the remaining approaches agreed with each other to within 35 %, which is of the order of the uncertainty of each individual approach. Strengths and weaknesses of the four approaches and the resulting consequences for deriving longer-term carbon balances are discussed.

Key words: ecosystem respiration, eddy covariance, chamber measurements, uncertainty analysis