Estimates of regional surface carbon dioxide exchange and carbon and oxygen isotope discrimination during photosynthesis from concentration profiles in the atmospheric boundary layer

Abstract

The integrating properties of the atmospheric boundary layer allow the influence of surface exchange processes on the atmosphere to be quantified and estimates of large-scale fluxes of trace gases and plant isotopic discrimination to be made. Five flights were undertaken over two days in and above the convective boundary layer (CBL) in a vegetated region in central Siberia. Vertical profiles of CO 2 and H 2 O concentrations, temperature and pressure were obtained during each flight. Air flask samples were taken at various heights for carbon and oxygen isotopic analysis of CO 2 . Two CBL budget methods were compared to estimate regional surface fluxes of CO 2 and plant isotopic discrimination against 13 CO 2 and C 18 O 16 O. Flux estimates were compared to ground-based eddy covariance measurements. The fluxes obtained for CO 2 using the first method agreed to within 10% of fluxes measured in the forest at the study site by eddy covariance. Those obtained from the second method agreed to within 35% when a correction was applied for air loss out of the integrating column and for subsidence. The values for 13 C discrimination were within the range expected from knowledge of C 3 plant discriminations during photosynthesis, while the inferred 18 O discrimination varied considerably over the two-day period. This variation may in part be explained by the enrichment of chloroplast water during the day due to evaporation from an initial signature in the morning close to source water. Additional potential complications arising from the heterogeneous nature of the landscape are discussed.

The CarboEurope Regional Experiment Strategy

“…Without appreciation of this 3D context of the relation between surface fluxes and atmosphere we could not understand some of the patterns we observed from the aircraft. It is exactly this 3D context that has limited the usefulness of ID inversions such as the convective boundary layer technique (Styles et al 2002;Lloyd et al 2001;Laubach and Fritsch 2002).…”

On the Controls of Leaf-Water Oxygen Isotope Ratios in the Atmospheric Crassulacean Acid Metabolism Epiphyte Tillandsia usneoides

“…O (d 18 O L ) labels CO 2 and allows for partitioning of the gross components of net CO 2 flux from ecosystem to regional scales (Yakir and Wang, 1996;Ciais et al, 1997;Styles et al, 2002;Cuntz et al, 2003;Ogee et al, 2004;Helliker et al, 2005). The production of isotopically distinct O 2 by photosynthesis allows for global-scale estimates of productivity over millennia (Guy et al, 1993;Luz et al, 1999;Hoffmann et al, 2004).…”

Oxygen isotope content of CO2 in nocturnal ecosystem respiration: 2. Short‐term dynamics of foliar and soil component fluxes in an old‐growth ponderosa pine forest

“…[44] Efforts have been made to model the influence of terrestrial ecosystems on the oxygen isotope ratio of atmospheric CO 2 at regional, continental, and global scales [Ciais et al, 1997;Peylin et al, 1999;Cuntz et al, 2002Cuntz et al, , 2003aCuntz et al, , 2003bStyles et al, 2002;Ishizawa et al, 2002]. These models are fundamentally dependent on knowledge of the isotopic composition of precipitation, which is also typically modeled [e.g., Cuntz et al, 2003aCuntz et al, , 2003b.…”