Effects of intraleaf variations in carbonic anhydrase activity and gas exchange on leaf C18OO isoflux in Zea mays
2006
Affek, Hagit P. | Krisch, Maria J. | Yakir, Dan
• Variation in the C¹⁸OO content of atmospheric CO₂ (δ¹⁸Oₐ) 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 (δ¹⁸Ow). • Here we tested the hypothesis that mean leaf δ¹⁸Ow 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 δ¹⁸Ow (7 to 21‰), δ¹⁸O and δ¹³C of leaf organic matter (25 to 30‰ and −12.8 to −13.2‰, respectively), and substomatal CO₂ concentrations (intercellular CO₂ concentrations, cᵢ, at the leaf center were ∼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 ∼10%. Conversely, use of measured parameters from a leaf segment could produce large errors in predicting leaf‐integrated C¹⁸OO fluxes.
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