Can Oxygen Isotopes in Tree Rings Be Used to Detect Stomatal Responses to Global Change?

Area of Science:

• Plant ecophysiology
• Paleoclimatology
• Isotope geochemistry

Background:

• Stomatal conductance (gs) controls plant gas exchange, but its long-term response to rising CO2 and climate change is debated.
• Tree ring stable oxygen isotopes (δ18Otrc) are proposed to reflect past gs, but their sensitivity to environmental drivers needs evaluation.
• Previous studies using δ18Otrc suggest minimal changes in gs since pre-industrial times, yet this is questioned.

Purpose of the Study:

• To assess the sensitivity of tree ring oxygen isotopes (δ18Otrc) to changes in stomatal conductance (gs) under rising CO2 and climate change.
• To evaluate the influence of vapor pressure deficit (VPD) and temperature on δ18Otrc trends, independent of gs.
• To determine the reliability of δ18Otrc for inferring long-term gs trends.

Main Methods:

• Utilized current theoretical models to simulate δ18Otrc trends.
• Analyzed the impact of temporal changes in gs, VPD, and temperature on δ18Otrc since the early 20th century.
• Investigated the role of the Péclet effect in linking gs changes to δ18Otrc.

Main Results:

• Temporal changes in gs only significantly impact δ18Otrc trends in dry climates with the Péclet effect present.
• Increases in VPD and temperature have a much larger influence on δ18Otrc trends than gs changes.
• The sensitivity of δ18Otrc to detect gs changes is limited, especially under non-Péclet conditions.

Conclusions:

• Interpreting long-term gs trends from δ18Otrc requires caution due to confounding environmental factors.
• VPD and temperature are dominant drivers of δ18Otrc trends, making unambiguous attribution to gs challenging.
• Future research should refine methods to disentangle the effects of gs, VPD, and temperature for accurate paleoclimate reconstructions.