Pan-european delta 13C values of air and organic matter from forest ecosystems

We present carbon stable isotope, d13C, results from air and organic matter samplescollected during 98 individual field campaigns across a network of Carboeuroflux forestsites in 2001 (14 sites) and 2002 (16 sites). Using these data, we tested the hypothesis thatd13C values derived from large-scale atmospheric measurements and models, which areroutinely used to partition carbon fluxes between land and ocean, and potentiallybetween respiration and photosynthesis on land, are consistent with directly measuredecosystem-scale d13C values. In this framework, we also tested the potential of d13C incanopy air and plant organic matter to record regional-scale ecophysiological patterns.Our network estimates for the mean d13C of ecosystem respired CO2 and the related'discrimination' of ecosystem respiration, der and Der, respectively, were 25.6 1.9% and17.8 2.0% in 2001 and 26.6 1.5% and 19.0 1.6% in 2002. The results were in closeagreement with d13C values derived from regional-scale atmosphericmeasurement programsfor 2001, but less so in 2002, which had an unusual precipitation pattern. This suggests thatregional-scale atmospheric sampling programs generally capture ecosystem d13C signalsover Europe, but may be limited in capturing some of the interannual variations.