Journal
NEW PHYTOLOGIST
Volume 223, Issue 4, Pages 1834-1843Publisher
WILEY
DOI: 10.1111/nph.15922
Keywords
climate change; drought; ecophysiology; foliar color; hydraulic failure; tree die-off; tree mortality; tree physiology
Categories
Funding
- NSF Graduate Research Fellowship Program
- Oklahoma NSF EPSCoR Research Infrastructure Improvement Award [OIA-1301789]
- Oklahoma State University College of Arts Sciences
- Department of Natural Resources Ecology and Management at Oklahoma State University
- McIntire-Stennis project [OKL0 2929]
- David and Lucille Packard Foundation
- University of Utah Global Change and Sustainability Center, NSF Grants [1714972, 1802880]
- USDA National Institute of Food and Agriculture, Agricultural and Food Research Initiative Competitive Program, Ecosystem Services and Agro-ecosystem Management [2018-67019-27850]
- Direct For Biological Sciences
- Division Of Environmental Biology [1802880] Funding Source: National Science Foundation
- Division Of Environmental Biology
- Direct For Biological Sciences [1714972] Funding Source: National Science Foundation
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Determining physiological mechanisms and thresholds for climate-driven tree die-off could help improve global predictions of future terrestrial carbon sinks. We directly tested for the lethal threshold in hydraulic failure - an inability to move water due to drought-induced xylem embolism - in a pine sapling experiment. In a glasshouse experiment, we exposed loblolly pine (Pinus taeda) saplings (n = 83) to drought-induced water stress ranging from mild to lethal. Before rewatering to relieve drought stress, we measured native hydraulic conductivity and foliar color change. We monitored all measured individuals for survival or mortality. We found a lethal threshold at 80% loss of hydraulic conductivity - a point of hydraulic failure beyond which it is more likely trees will die, than survive, and describe mortality risk across all levels of water stress. Foliar color changes lagged behind hydraulic failure - best predicting when trees had been dead for some time, rather than when they were dying. Our direct measurement of native conductivity, while monitoring the same individuals for survival or mortality, quantifies a continuous probability of mortality risk from hydraulic failure. Predicting tree die-off events and understanding the mechanism involved requires knowledge not only of when trees are dead, but when they begin dying - having passed the point of no return.
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