Journal
SCIENCE
Volume 291, Issue 5513, Pages 2584-2587Publisher
AMER ASSOC ADVANCEMENT SCIENCE
DOI: 10.1126/science.1056374
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The oxygen-18 (O-18) content of atmospheric carbon dioxide (CO2) is an important indicator of CO2 uptake on land. It has generally been assumed that during photosynthesis, oxygen in CO2 reaches isotopic equilibrium with oxygen in O-18-enriched water in leaves. We show, however, large differences in the activity of carbonic anhydrase (which catalyzes CO2 hydration and O-18 exchange in leaves) among major plant groups that cause variations in the extent of O-18 equilibrium (theta (eq)). A clear distinction in theta (eq) between C-3 trees and shrubs, and C-4 grasses makes atmospheric (COO)-O-18 a potentially sensitive indicator to changes in C-3 and C-4 productivity. We estimate a global mean theta (eq) value of similar to0.8, which reasonably reconciles inconsistencies between O-18 budgets of atmospheric O-2 (Dole effect) and CO2.
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