Tree-Ring Signatures of CO2 Fertilization and Altered Drought Resilience |
Alexander J. Winkler,
Jacob Nelson,
Mukund Palat Rao,
Lisa Wingate
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Project descriptionTree rings serve as invaluable archives of climate history, recording forest responses to rising atmospheric CO2 and climatic extremes while illuminating key physiological processes. Elevated CO2 enrichment is expected to trigger enhanced photosynthetic productivity (the CO2 fertilization effect). Concurrently, rising CO2 also triggers stomatal closure dynamics—allowing trees to reduce water loss through transpiration while maintaining sufficient CO2 uptake. This CO2-response potentially enhances tree resilience under drought stress, suggesting a changing forest responses to aridity under elevated CO2. Earth system models incorporate these mechanisms, projecting strong CO2-driven feedbacks that modulate future climate trajectories; the magnitude of these effects remains uncertain, however, should leave a discernible imprint in tree-ring records.This project leverages the rich temporal resolution of tree-ring data to address critical knowledge gaps in forest responses to rising CO2. First, we will analyze tree-ring records—including isotopic signatures reflecting photosynthetic mechanisms—to identify distinct CO2 signatures and quantify forest biomass responses. Using causal inference methods (e.g., Zhan et al., 2024), we will disentangle productivity and drought response dynamics from confounding factors to test theoretical expectations of CO2 fertilization. Second, we will assess the temporal evolution of CO2 sensitivity in trees, evaluating hypotheses regarding potential saturation of the fertilization effect. Third, we will integrate tree-ring data with complementary spatial datasets (e.g., FLUXNET, remote sensing) to investigate forest-climate interactions under rising CO2. This analysis will ultimately provide data-driven insights that serve as critical constraints for Earth system models, refining projections of forest development and its role in the global carbon cycle. Working group and planned collaborationsThe successful PhD candidate will work in the Atmosphere-Biosphere Coupling, Climate and Causality group of the Department of Biogeochemical Integration at the Max Planck Institute for Biogeochemistry. The project is embedded in the MC3 4 Earth Max Planck Center - a collaboration between:
Your profileThe ideal candidate has the following qualifications:
ReferencesZhan, C., Orth, R., Yang, H., Reichstein, M., Zaehle, S., De Kauwe, M.G., Rammig, A., Winkler, A.J., 2024. Estimating the CO2 Fertilization Effect on Extratropical Forest Productivity From Flux-Tower Observations. Journal of Geophysical Research: Biogeosciences 129, e2023JG007910. https://doi.org/10.1029/2023JG007910![]() |