Affiliation:
1. Department of Environmental Science and Energy Research, Weizmann Institute of Science, Rehovot 76100, Israel.
Abstract
The oxygen-18 (
18
O) content of atmospheric carbon dioxide (CO
2
) is an important indicator of CO
2
uptake on land. It has generally been assumed that during photosynthesis, oxygen in CO
2
reaches isotopic equilibrium with oxygen in
18
O-enriched water in leaves. We show, however, large differences in the activity of carbonic anhydrase (which catalyzes CO
2
hydration and
18
O exchange in leaves) among major plant groups that cause variations in the extent of
18
O equilibrium (θ
eq
). A clear distinction in θ
eq
between C
3
trees and shrubs, and C
4
grasses makes atmospheric C
18
OO a potentially sensitive indicator to changes in C
3
and C
4
productivity. We estimate a global mean θ
eq
value of ∼0.8, which reasonably reconciles inconsistencies between
18
O budgets of atmospheric O
2
(Dole effect) and CO
2
.
Publisher
American Association for the Advancement of Science (AAAS)
Cited by
154 articles.
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