Abstract Detail


Velasco, Vera [1], Noordermeer, Devin [1], Sen, Tomoyuki [1], Tongson, Eden [2], Fuentes, Sigfredo [3], Ensminger, Ingo [1].

Douglas-fir does not recover from co-occuring heat and drought with rewatering.

Prolonged drought and co-occurring drought and heat events (heatwave) pose a significant risk to growth and development of long-lived tree species including those acclimated to a range of environments such as conifers. Douglas-fir is one economically important conifer species found from coastal and interior areas of British Columbia (BC), Canada to Mexico. We hypothesized that among Douglas-fir provenances, those from areas with low mean annual precipitation (MAP) and elevated mean annual temperature (MAT) can fully recover from drought and heatwave with watering. So, we grew Douglas-fir provenances from Little Elk and Meldrum Creek from interior BC (interior variety) and Pemberton and Tsowwin River from coastal areas of BC (coastal variety). Among these places of origin, MAP and MAT from 1961 to 1990 were highest in Tsowwin River and lowest at Little Elk. We studied several water-related traits, rates of photosynthesis, and capacity to regulate absorbed light when exposed to CW (22°C + watering; control), CD (four weeks of 22 °C) and HD (two weeks of CD, followed by two weeks of 40 °C and drought combined). Plants were rewatered for two weeks after CD (CD+W) and HD (HD+W). All provenances exposed to CD had decreased water status compared to control, as shown by low water content (RWC), low water potential (Ψw) and negligible evapotranspiration rate. Also, the proportion of light used for photosynthesis (ФPSII) and photosynthetic rates were lower under CD. After 2 weeks of rewatering, we found Little Elk was not able to fully recover RWC after CD+W while others fully recovered. The provenances that successfully recovered from CD also showed heightened levels of evapotranspiration to levels similar to control, and allocation of light for photosynthesis similar to control. As in CD, exposure to HD led to lower RWC, Ψw and evapotranspiration rates in all Douglas-fir provenances. However, light regulation varied with only Little Elk and Tsowwin River provenances showing lower ФPSII. The other two provenances, Meldrum Creek and Pemberton, favored photochemistry as shown by increased ФPSII. As expected, we observed lower photosynthetic rates to levels close to zero in provenances with decreased water status and less light for photosynthesis in response to HD. But we also observed lower gas exchange rates in provenances Meldrum Creek and Pemberton regardless of increased ФPSII. This suggests water availability is always a limiting factor in photosynthesis and that an increased proportion of light towards photochemistry does not alleviate stress due to HD. Unfortunately, rewatering after several weeks of exposure to HD did not provide relief to any Douglas-fir provenance with water status, ФPSII, and gas exchange rates remaining low. Taken together, we showed that Douglas-fir provenances adapted to higher temperatures and low precipitation have the capacity to acclimate to and recover from drought through plasticity in water regulation and light dissipation. However, this cannot be said for heatwave.

1 - University of Toronto, Biology, 3359 Mississauga Rd, Mississauga, ON, L5L1C6, Canada
2 - University of Melbourne
3 - University of Melbourne, 3359 Mississauga Rd, Mississauga, ON, L5L1C6, Canada

gas exchange
thermal imaging
Chlorophyll fluorescence
light regulation
Interior Douglas-fir
Coastal Douglas-fir
climate change.

Presentation Type: Oral Paper
Number: EPH3003
Abstract ID:253
Candidate for Awards:None

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