title: Zeaxanthin-independent energy quenching and alternative electron sinks cause a decoupling of the relationship between the photochemical reflectance index (PRI) and photosynthesis in an evergreen conifer during spring.
abstract: In evergreen conifers, the winter down-regulation of photosynthesis and its recovery during spring are the result of a reorganization of the chloroplast and adjustments of energy-quenching mechanisms. These phenological changes may remain undetected by remote sensing, as conifers retain green foliage during periods of photosynthetic down-regulation. The aim was to assess if the timing of the spring recovery of photosynthesis and energy-quenching characteristics are accurately monitored by the photochemical reflectance index (PRI) in the evergreen conifer Pinus strobus. The recovery of photosynthesis was studied using chlorophyll fluorescence, leaf gas exchange, leaf spectral reflectance, and photosynthetic pigment measurements. To assess if climate change might affect the recovery of photosynthesis, seedlings were exposed to cold spring conditions or warm spring conditions with elevated temperature. An early spring decoupling of the relationship between photosynthesis and PRI in both treatments was observed. This was caused by differences between the timing of the recovery of photosynthesis and the timing of carotenoid and chlorophyll pool size adjustments which are the main factors controlling PRI during spring. It was also demonstrated that zeaxanthin-independent NPQ mechanisms undetected by PRI further contributed to the early spring decoupling of the PRI-LUE relationship. An important mechanism undetected by PRI seems to involve increased electron transport around photosystem I, which was a significant energy sink during the entire spring transition, particularly in needles exposed to a combination of high light and cold temperatures.
authors.affiliation: Department of Biology, University of Toronto at Mississauga, 3359 Mississauga Road, ON, Canada Graduate Department of Cell & Systems Biology, University of Toronto, Toronto, ON, Canada.
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Fréchette
authors.affiliation: Department of Biology, University of Toronto at Mississauga, 3359 Mississauga Road, ON, Canada Graduate Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada.
authors.forename: Christopher Y S
authors.initials: CY
authors.lastname: Wong
authors.affiliation: Department of Biology, University of Toronto at Mississauga, 3359 Mississauga Road, ON, Canada Graduate Department of Cell & Systems Biology, University of Toronto, Toronto, ON, Canada.
authors.forename: Laura Verena
authors.initials: LV
authors.lastname: Junker
authors.affiliation: Department of Biology, University of Toronto at Mississauga, 3359 Mississauga Road, ON, Canada Graduate Department of Cell & Systems Biology, University of Toronto, Toronto, ON, Canada.
authors.forename: Christine Yao-Yun
authors.initials: CY
authors.lastname: Chang
authors.affiliation: Department of Biology, University of Toronto at Mississauga, 3359 Mississauga Road, ON, Canada Graduate Department of Cell & Systems Biology, University of Toronto, Toronto, ON, Canada Graduate Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada ingo.ensminger@utoronto.ca.
authors.forename: Ingo
authors.initials: I
authors.lastname: Ensminger
mesh_terms: D004583:Electrons; D004734:Energy Metabolism; D010777:Photochemistry; D010788:Photosynthesis; D028223:Pinus / Q000502:physiology*; D012621:Seasons; D013696:Temperature; D065146:Zeaxanthins
chemical_list: D065146:Zeaxanthins
keywords: Climate change; Eastern white pine (Pinus strobus); leaf pigments; light-use efficiency of photosynthesis; photochemical and non-photochemical quenching; photochemical reflectance index; spring recovery of photosynthesis; xanthophyll cycle.