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Grantee Research Project Results

Grantee Research Project Results

Temperature Sensitivity and Physiological Mechanism of Drought-Induced Tree Mortality: Improving Assessments of Global Change Impacts

EPA Grant Number: FP917178
Title: Temperature Sensitivity and Physiological Mechanism of Drought-Induced Tree Mortality: Improving Assessments of Global Change Impacts
Investigators: Adams, Henry David
Institution: University of Arizona
EPA Project Officer: Just, Theodore J.
Project Period: September 1, 2010 through August 31, 2013
Project Amount: $111,000
RFA: STAR Graduate Fellowships (2010)
Research Category: Fellowship - Global Change , Academic Fellowships

Description:

Objective:

To improve predictions of ecosystem vulnerability to global change, I will continue my dissertation research examining the temperature sensitivity and physiological mechanism of drought-induced tree mortality in pinyon pine (Pinus edulis) using a combination of experimental approaches to simulate drought under ambient and warmer (4 °C) drought conditions. Specifically this grant supports analyses of tree mobile carbohydrates to test two hypotheses for the physiological mechanism of tree drought mortality: 1) that trees die from drought when respiratory demands deplete mobile carbohydrate resources, and 2) that trees die from drought when failure of mobile carbohydrate translocation to sink tissues occurs.

Synopsis
With the current trends in global change, droughts will be more frequent, which could disrupt the carbon storage function of forest ecosystems, leading to accelerated global warming. Therefore, understanding how trees die from drought in a warmer world is critical for predicting whether forests will continue to sequester a portion of carbon dioxde released by human activities. This project calls for experimentally killing trees with rought to measure the temperature sensitivity and physiology of tree death from drought.

Approach:

This project takes advantage of three pinyon pine drought mortality experiments that explore the temperature sensitivity of drought mortality: one already completed with transplanted trees in a glasshouse; an ongoing experiment with transplanted trees under realistic field conditions; and a planned growth chamber experiment with tree seedlings. Testing hypotheses for the physiological mechanism of drought will be accomplished by analyzing a time series of tissue collected during drought through mortality for concentration of mobile carbohydrates, including sugars and starches. These analyses will include leaf (pine needle) tissue collected from the glasshouse and field experiments as well as whole-plant, leaf, root, and stem mobile carbohydrates from seedlings in the growth chamber experiment, which will include samples from trees grown under four temperature regimes.

Expected Results:

I expect that leaf mobile carbohydrate concentrations from the glasshouse and field experiments will decline as the trees approach death, reflecting previously observed trends in respiration during the glasshouse drought experiment and supporting hypothesis 1 as the mechanism of drought-induced tree mortality for pinyon. I also expect that mobile carbohydrate concentrations from the growth chamber experiment in foliar, stem, and root tissue will decline similarly through drought-induced mortality, analogous to trends expected for the glasshouse and field experiments both for carbon resources and gas exchange. However, if mobile carbohydrates do not decline through drought mortality in some tissues, this will provide evidence in support of carbohydrate translocation failure (hypothesis 2 above).

Potential to Further Environmental/Human Health Protection
Shifts in biosphere-atmosphere feedbacks remain a critical gap in our understanding of global change impacts. One challenge is to predict plant responses to extreme climate events, such as droughts, in a warmer world. Estimates of future carbon budgets assume continued uptake of atmospheric CO2 by the biosphere. Therefore, quantifying the vulnerability of terrestrial biosphere carbon sinks is critical for current global change science. A key to predicting the ability of forests to continue sequestering atmospheric CO2 is an understanding of how trees die, specifically the temperature sensitivity and physiological mechanism of drought-induced tree mortality. Tree mortality has the potential to influence regional water budgets, affecting regional water quality and availability, yet research that addresses these issues is notably lacking.

Supplemental Keywords:

tree drought mortality, global change, mobile carbohydrates, biosphere-atmosphere feedbacks,

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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