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Murphy, Bridget K. [1], Lorusso, Sara [1], Ensminger, Ingo [1].

Effects of warming and reduced soil moisture on autumn cold acclimation in field-grown white spruce.

Temperature and photoperiod are critical environmental cues for the seasonal regulation of carbon uptake in boreal conifers. During autumn, the downregulation of photosynthesis is triggered by both decreasing temperatures and shortening photoperiods. While photoperiod will be unaffected by climate change, it is unclear how future warming and reduced water availability will impact the regulation of autumn cold acclimation. Genetic variation may also affect the timing of autumn cold acclimation due to local adaptions to environment and photoperiod. The goal of our project is to understand the impact of warming and the relative importance of photoperiod on the timing of cold acclimation in two latitudinally distinct white spruce (Picea glauca) genotypes when grown under similar environmental conditions. The experimental design was full factorial, consisting of four treatments in replicate experimental field plots: (1) control, (2) reduced soil moisture, (3) warming and (4) warming combined with reduced soil moisture. Warming was achieved through a temperature free-air enhancement experimental set up and soil moisture was reduced using rainout structures. To track intraspecific variation of autumn phenology, we measured chlorophyll fluorescence and spectral reflectance across time points from summer to late autumn. Across all time points, there were strong genotype, treatment, and genotype x treatment effects on photosystem II (PSII) efficiency, non-photochemical quenching (NPQ), photochemical reflectance indices (PRI), and chlorophyll carotenoid indices (CCI). Genotype and treatment differences became evident in late autumn as temperatures decreased and photoperiods shortened. From early November onwards, the southern genotype showed higher PSII efficiency, PRI, CCI and dynamic NPQ, compared to the northern genotype, characteristic of delayed cold acclimation. From late November onwards, control and drought treatments had lower PSII efficiency, PRI, CCI, and higher sustained NPQ compared to the warming and warming combined with reduced soil moisture treatments. Our findings provide evidence that delays in the downregulation of photosynthesis and the upregulation of sustained NPQ occur under warming and are greater in southern white spruce genotypes compared to northern genotypes.

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1 - University of Toronto Mississauga, Department of Biology, 3359 Mississauga Rd. , Mississauga, ON, L5L1C6, Canada

low temperature acclimation
cold hardening
white spruce
climate change
genotypic variation

Presentation Type: Oral Paper
Session: PHYS, Physiology
Location: /
Date: Wednesday, July 21st, 2021
Time: 1:30 PM(EDT)
Number: PHYS011
Abstract ID:709
Candidate for Awards:Physiological Section Physiological Section Li-COR Prize,Physiological Section Best Paper Presentation

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