title: Effects of intraleaf variations in carbonic anhydrase activity and gas exchange on leaf C18OO isoflux in Zea mays.
abstract: Variation in the C18OO content of atmospheric CO2 (delta18Oa) can be used to distinguish photosynthesis from soil respiration, which is based on carbonic anhydrase (CA)-catalyzed 18O exchange between CO2 and 18O-enriched leaf water (delta18Ow). Here we tested the hypothesis that mean leaf delta18Ow and assimilation rates can be used to estimate whole-leaf C18OO flux (isoflux), ignoring intraleaf variations in CA activity and gas exchange parameters. We observed variations in CA activity along the leaf (> 30% decline from the leaf center toward the leaf ends), which were only partially correlated to those in delta18Ow (7 to 21 per thousand), delta18O and delta13C of leaf organic matter (25 to 30 per thousand and -12.8 to -13.2 per thousand, respectively), and substomatal CO2 concentrations (intercellular CO2 concentrations, c(i), at the leaf center were approximately 40% of those at the leaf tip). The combined effect of these variations produced a leaf-integrated isoflux that was different from that predicted based on bulk leaf values. However, because of canceling effects among the influencing parameters, isoflux overestimations were only approximately 10%. Conversely, use of measured parameters from a leaf segment could produce large errors in predicting leaf-integrated C18OO fluxes.
authors.affiliation: Department of Environmental Sciences and Energy Research, Weizmann Institute, Rehovot 76100, Israel.
authors.forename: Hagit P
authors.initials: HP
authors.lastname: Affek
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Krisch
authors.forename: Dan
authors.initials: D
authors.lastname: Yakir
mesh_terms: D002244:Carbon / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism*; D002256:Carbonic Anhydrases / Q000378:metabolism*; D019069:Cell Respiration; D008027:Light; D010100:Oxygen / Q000378:metabolism; D010103:Oxygen Isotopes; D010788:Photosynthesis; D018515:Plant Leaves / Q000201:enzymology* / Q000378:metabolism*; D018526:Plant Transpiration; D003313:Zea mays / Q000201:enzymology* / Q000378:metabolism
chemical_list: D010103:Oxygen Isotopes; D002245:Carbon Dioxide; D002244:Carbon; D002256:Carbonic Anhydrases; D010100:Oxygen