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Can oxygen isotopes in tree rings be used to detect stomatal responses to global change?

Carter, Imogen1; Brienen, Roel1; Gloor, Manuel1

Published Nov 11, 2025 on Dryad. https://doi.org/10.5061/dryad.905qftv01

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Abstract

Stomatal conductance (gs) regulates CO2 and water fluxes of plants. Although experiments have shown that gs decreases with elevated CO2, it is unclear how gs is responding in-situ to long-term exposures to rising CO2 and a changing climate. Tree ring isotope analysis provides a unique method to assess tree ecophysiological responses to long-term exposures to slowly changing environmental conditions. In particular, it has been suggested that changes in gs can potentially be inferred from tree ring stable oxygen isotope ratios (δ18Otrc). Several studies have indeed used δ18Otrc trends to conclude that gs has not significantly changed from pre-industrial values. However, it remains unclear whether δ18Otrc is sufficiently sensitive to detect the magnitude of change in gs expected due to CO2 increases and climatic changes. We deposit here the climate data and R scripts that we use to evaluate the sensitivity of δ18Otrc trends to CO2 and climate-induced changes in gs, and to VPD and temperature increases since the beginning of the 20th century, using current theoretical models. We find that temporal changes in gs only significantly affect δ18Otrc trends when the Péclet effect is present, and then only in dry climates. In contrast to the weak effects of gs on δ18Otrc trends, we find that temporal increases in VPD and temperature, independent of changes in gs, have far greater contributions to δ18Otrc trends. Thus, this increasingly popular method should be used with caution, because it is highly challenging to unambiguously attribute trends in δ18Otrc to changes in gs.