Global Plant Transpiration and Its Response to Rising Atmospheric CO2

Large uncertainty exists in predictions of future transpiration due to complex interactions between plant physiology and the water and energy budgets.

A scheme including the direct and indirect effects of elevated CO2 on plant transpiration (Et), including positive influences on Et (red), a negative influence on Et (blue), and climate fluxes and influences (black).

[Reprinted under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0) from Vicente-Serrano, S., et al. "The Uncertain Role of Rising Atmospheric CO2 on Global Plant Transpiration." Earth Science Reviews 230 104055 (2022). DOI:10.1016/j.earscirev.2022.104055.]

The Science

Plant transpiration is the largest hydrologic flux of water globally after precipitation and therefore plays a large role in driving surface water availability. Transpiration responds to rising atmospheric carbon dioxide (CO2) at stomatal to whole plant to regional scales, with feedbacks between scales. This study reviewed the biophysical mechanisms by which rising CO2 impacts global-scale plant transpiration and identified a path forward to improve predictions of transpiration under future conditions.

The Impact

Recent observations of rising plant transpiration at the global scale are consistent with increasing leaf area due to CO2 fertilization but at odds with the well-known stomatal closure response. The study provides a testable framework of hypotheses regarding how transpiration responds globally to rising atmospheric CO2 and stresses the need for empiricists and modelers to unify efforts to better understand and predict transpiration under future conditions.

Summary

In this study, researchers review the myriad ways by which rising CO2 can influence plant transpiration directly and indirectly at the global scale. Many compensating mechanisms and feedbacks make predicting transpiration challenging with rising CO2. Global changes in plant transpiration in response to rising CO2 will manifest through droughts, vapor pressure deficit, plant physiological processes including shifting leaf area and phenology, and forest loss (disturbance). The researchers place these mechanisms into a testable framework of hypotheses that outlines a path forward for both empiricists and modelers. The impacts of changing transpiration at large scales are significant for water provision and utilization demands.

Principal Investigator

Nate McDowell
Pacific Northwest National Laboratory
[email protected]

Program Manager

Brian Benscoter
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

This work was supported by the Next Generation Ecosystem Experiment-Tropics (NGEE-Tropics) through the Biological and Environmental Research (BER) Program within the U.S. Department of Energy’s (DOE) Office of Science, the Spanish Ministry of Science, FEDER, and the CROSSDRO project financed by the ERA-Net Consortium Assessment of Cross(X) – Sectorial Climate Impacts and Pathways for Sustainable Transformation (AXIS), which is the JPI-Climate co-funded call of the European Commission. Support was also received from the European Research Council and the European Union Horizon 2020 program.

References

Vicente-Serrano, S., et al. "The Uncertain Role of Rising Atmospheric CO2 on Global Plant Transpiration." Earth Science Reviews 230 104055  (2022). https://doi.org/10.1016/j.earscirev.2022.104055.