U.S. Department of Energy Office of Biological and Environmental Research

PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

A Multi-species Synthesis of Physiological Mechanisms in Drought-induced Tree Mortality

Nate McDowell
Pacific Northwest National Lab

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7/12/2017

The Science  

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

The Impact
This paper 1) tests a contentious hypothesis regarding hydraulic failure and carbon starvation, for the first time, at a global scale, 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 inhibits water transport, leading to desiccation. Carbon starvation is a phenomena 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 proceeding 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 in order to improve our understanding and predictions of ecosytems and vegetation.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
Nate McDowell
Pacific Northwest National Lab
nate.mcdowell@pnnl.gov

Funding
Funding was provided by DOE, Office of Science, NGEE-Tropics, via the Los Alamos and the Pacific Northwest National Lab’s LDRD program, and via NSF.

Publications
Adams et al. (61 co-authors). A multi-species synthesis of physiological mechanisms in drought-induced mortality. Nature Ecology and Evolution, in press.

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