drought and cold hardiness poster final
TRANSCRIPT
120°W126°W
CALIFORNIA
OREGON
WASHINGTON
Hardiness2High Low
120°W126°W
48°N
44°N
40°N
CALIFORNIA
OREGON
WASHINGTON
Hardiness1High Low
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Transpirationmin
•Seal end of twigwith wax
•Measure twig weight daily
•Transpirationmin=Slope of drying curve
00.20.40.60.8
11.21.4
0 5 10
Twig
wei
ght (
g)
Days
Mass loss/time
Water deficit
•Twig fresh weight (FW)
•Twig end in water, turgid weight (TW)
•Dry twig weight (DW)
•Water deficit= (TW-FW)/(TW-DW)
Specific leaf area
•Needles photographed
•Leaf areas (LA) with Image J
•Dry weight (DW)
•Specific leaf area= LA / DW
Drought-related ecophysiological traits
Not all populations of a species are created equal with respect to stress tol-erance.
The differences among populations are a product of climate-related natural selection.
Growing populations under similar conditions (common gardens) re-veals genetic varation in stress tolerance.
Garden conditions need to be stressful to induce the expressions of stress-response traits.
Droughty garden
Cold garden
Drought- sensitive
Drought- resistant
Ecophysiological traits associated with drought and cold hardiness are measured for each population.
The drought and cold hardiness trait data can be combined using Prin-cipal Components Analy-sis to determine how traits trend together, and to develop generalized stress hardiness traits (Hardiness1 and 2).
The stress hardiness traits are then modeled as a function of the popu-lations’ native climate (seed-source climate).
We conducted a common garden experiment with 35 populations of coastal Douglas-fir (Pseudotsuga menziesii var. menziesii) growing at droughty and cool common gardens.
We collected twig samples from 280 trees at each common garden in summer and fall 2012.
We measured three traits as-sociated with drought hardi-ness (see below). Cold hardi-ness was assessed using ar-tificial freeze tests.
Higher values of Hardiness1 corresponded with greater drought and cold hardiness.
Hardiness1 increasedwith colder winter temperatures.
Higher values of Hardiness2 corresponded with greater cold and lower drought hardiness.
Hardiness2 increasedwith higher summer -precipitation.
Hardiness2
The Theory The Study
Hardiness1
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onth
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Mea
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m)
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Sheel Bansal, [email protected], [email protected]
Sheel Bansal, Constance A. Harrington, J. Bradley St. ClairUSDA Forest Service, Pacific Northwest Research Station, Olympia Forestry Sciences Laboratory
-Moving up in elevation to cooler winter climates, Douglas-fir populations were more drought and cold hardy.-Why? Winter conditions can be very drying due to high vapor pressure deficit, frozen soils, and intercellular ice formation, leading to cellular dehydration. -Cellular dehydration induces a number of stress-induced genes and physiological adjustments, such as the accumulation of dehydrins, osmoprotectants, sugar alcohols and epicuticular waxes, which are common mechanisms for coping with winter or summer drought.
-Moving south in latitude to drier summer climates, Douglas-fir populations were more drought hardy, but less cold hardy.-Why? There are many differences between drought and cold stress regarding the environmental cues that trigger stress responses (osmotic stress vs. cold temps), the signaling pathways (ABA-dependent vs. -independent), and ultimate causes of cell death (ion toxicity vs. physical destruction). -The tradeoff in cold for drought hardiness was strongest for needle, moderate for bud and absent for stem tissues, suggesting the tradeoff mechanism may relate to photosynthesis.
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Har
dine
ss1
Seed-source climate
Populations from mild climates
Populations from harsh climates
Drought3Drought2
Drought1
Cold3
Cold2Cold1
We thank the J. Herbert Stone Nursery, Hancock Forest Management and the BLM for support
-Climatic extremes in summer (drought) and winter (cold snaps) are expected to increase in frequency and intensity with climate change.
-Widely distributed species, such as coastal Douglas-fir have considerable differences among populations in their abilities to tolerate drought and cold stress.
-There are overlapping physiological mechanisms for coping with drought and cold stress, meaning that populations well-adapted to drought may also be tolerant to cold, and vice versa.
-Modeling the geographic variation in tolerance to drought and cold together can help locate populations better adapted to future climate, and generally demonstrates how multiple traits change in concert with each other along climate gradients.
Take home messages
-Drought and cold hardiness converged among Douglas-fir populations along temperature gradients and diverged along precipitation gra-dients, suggesting both overlapping and conflicting stress-response mechanisms for coping with drought and cold.
-Forest managers selecting populations for tolerance to one stressor must consider the linkages to non-target stressors that may have convergent (but possibly divergent) mechanisms of tolerance.
-Our findings highlight the necessity to look beyond bivariate trait-climate relationships, and instead holistically consider multiple traits and climate variables to effectively model and manage for the impacts of climate change on widespread species.
Finding Plants Adapted to Climatic Extremes: Drought and Cold Tolerance of Douglas-fir
Populations originating in regions with cold winters had increased drought and cold hardiness, which is likely due to conserved adaptations for coping with winter desiccation
Populations originating in regions with dry summers had increased drought hardiness but reduced cold hardiness, suggesting a conflict between tolerance mechanisms