Global patterns in leaf 13C discrimination and implications for studies of past and future climate

Aaron F. Diefendorf, Kevin E. Mueller, Scott L. Wing, Paul L. Koch, Katherine H. Freeman

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Abstract

Fractionation of carbon isotopes by plants during CO2 uptake and fixation (Δleaf) varies with environmental conditions, but quantitative patterns of Δleaf across environmental gradients at the global scale are lacking. This impedes interpretation of variability in ancient terrestrial organic matter, which encodes climatic and ecological signals. To address this problem, we converted 3,310 published leaf δ13C values into mean Δleaf values for 334 woody plant species at 105 locations (yielding 570 species-site combinations) representing a wide range of environmental conditions. Our analyses reveal a strong positive correlation between Δleaf and mean annual precipitation (MAP; R2 = 0.55), mirroring global trends in gross primary production and indicating stomatal constraints on leaf gas-exchange, mediated by water supply, are the dominant control of Δleaf at large spatial scales. Independent of MAP,we show a lesser, negative effect of altitude on Δleaf and minor effects of temperature and latitude. After accounting for these factors, mean Δleaf of evergreen gymnosperms is lower (by 1-2.7%) than for other woody plant functional types (PFT), likely due to greater leaf-level water-use efficiency. Together, environmental and PFT effects contribute to differences in mean Δleaf of up to 6% between biomes. Coupling geologic indicators of ancient precipitation and PFT (or biome) with modern Δleaf patterns has potential to yield more robust reconstructions of atmospheric δ13C values, leading to better constraints on past greenhouse-gas perturbations. Accordingly, we estimate a 4.6% decline in the δ13C of atmospheric CO2 at the onset of the Paleocene-Eocene Thermal Maximum, an abrupt global warming event ∼55.8 Ma.

Original languageEnglish (US)
Pages (from-to)5738-5743
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume107
Issue number13
DOIs
StatePublished - Mar 30 2010

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