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PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

A Multi-Species Synthesis of Physiological Mechanisms in Drought-Induced Tree Mortality

Nate McDowell

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July 12, 2017

Incorporating hydraulic failure as a trigger to plant mortality will improve understanding and predictions of ecosytems and vegetation.

The Science  
This is the first paper to synthesize the results on mechanisms of mortality from all known drought manipulation studies, and the synthesis found that hydraulic failure is a universal component of death while carbon starvation is frequent but not universal.

The Impact
This project (1) tests a contentious hypothesis regarding hydraulic failure and carbon starvation, for the first time, at a global scale, and (2) provides modelers a direct path to improving vegetation dynamics simulations.

Summary
About half of carbon dioxide emissions are absorbed by plants, but this service is threatened by increasing frequency of hot droughts. One of the largest uncertainties in land surface modeling is how vegetation will respond to greater exposure to life-threatening droughts. One of the most contentious theories in ecology today regards the mechanisms of responses (e.g., how plants regulate hydraulic failure and carbon starvation, if they even occur at all) during drought. Hydraulic failure is where plants experience partial or complete interruption of the water-transporting xylem tissue function from stress-induced embolisms that inhibit water transport, leading to desiccation. Carbon starvation is a phenomenon where an imbalance between carbohydrate demand and supply leads to an inability to meet osmotic, metabolic, and defensive carbon requirements. This study reviewed and synthesized the findings on all known drought studies that killed trees and found the occurrence of hydraulic failure was a universal characteristic preceding plant death, and co-occurring carbon starvation occurred in approximately 50% of studies. The most advanced land-surface models today simulate mortality via carbon starvation but not via hydraulic failure. Therefore, current model development should incorporate hydraulic failure as a trigger to plant mortality to improve understanding and predictions of ecosytems and vegetation.

Contacts
BER Program Manager
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Principal Investigator
Nate McDowell
Pacific Northwest National Laboratory
Richland, WA 99354
nate.mcdowell@pnnl.gov

Funding
Funding was provided through the Next-Generation Ecosystem Experiments (NGEE)–Tropics of the Office of Biological and Environmental Research (BER), within the U.S. Department of Energy Office of Science; the Los Alamos National Laboratory's and Pacific Northwest National Laboratory’s Laboratory-Directed Research and Development (LDRD) programs; and the National Science Foundation.

Publications
Adams, H.D., et al. "A multi-species synthesis of physiological mechanisms in drought-induced mortality." Nature Ecology & Evolution 1, 1285–1291 (2017). [DOI:10.1038/s41559-017-0248-x]

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