Thermotolerance (heat tolerance)

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How does foliar thermotolerance vary by:
-leaf age?
-species?
-within-species populations from contrasting climates?
​We ask these types of questions to understand how agricultural (Coffea arabica) and forest (Pinus ponderosa, Pseudotsuga menziesii, Pinus edulis, Juniperus monosperma, Pinus albicaulis) species will respond to warmer temperatures. We measure thermotolerance curves using 2 independent methods: chlorophyll fluorescence and electrolyte leakage. 

Marias et al. (2016) Trees
Marias et al. (2016) Tree Physiology

Thermotolerance curves with Fv/Fm measured on Douglas-fir (PSME) and Ponderosa pine (PIPO) seedlings. PIPO was unexpectedly less heat tolerant than PSME, despite PIPO generally occupying sunnier, warmer, drier sites than PSME. But why??? We are working on this question.

Energy leaves absorb from the sun is used in 3 different processes: 1) photosynthesis, 2) chlorophyll fluorescence, and 3) heat dissipation. We use Fv/Fm as a proxy for photosynthetic performance.

Action shot of the chlorophyll fluorometer measuring Fv/Fm (the ratio of variable to maximum fluorescence)

Thermotolerance curves with Fv/Fm measured on coffee (Coffea arabica) to determine the effect of leaf age on thermotolerance. Older, mature leaves are more heat tolerant than younger, expanding leaves.