Seasonal acclimation of photosystem II in Pinus sylvestris. I. Estimating the rate constants of sustained thermal energy dissipation and photochemistry
Albert Porcar-Castell (1, 2), Eija Juurola (1), Eero Nikinmaa (1), Frank Berninger (3), Ingo Ensminger (4, 5) and Pertti Hari (1)
1. Department of Forest Ecology, University of Helsinki, P.O. Box 27, 00014 Helsinki, Finland / 2. Corresponding author () / 3. Département des sciences biologiques, Université du Québec à Montréal, CP 8888, succ. Centre-ville, Montreal, QC H3C 3P8,
Canada / 4. Department of Biology and Biotron, University of Western Ontario, London, ON N6A 5B7, Canada / 5. Present address: Department of Forest Ecology, Forest Research Institute Baden-Wuerttemberg, 79100 Freiburg, Germany / Received September 10, 2007; accepted June 6, 2008; published online August 1, 2008
Summary
Acclimation of the partitioning of absorbed light energy in Photosystem II (PSII) between photochemical and non-photochemical
processes includes short-term adjustments that are rapidly reversed in the dark and seasonal acclimation processes that are
unaffected by dark acclimation. Thus, by using dark-acclimated leaves to study the seasonal acclimation of PSII, the confounding
effect of short-term adjustments is eliminated. The maximum quantum yield of photochemistry, estimated by chlorophyll fluorescence
analysis as Fv/Fm, where Fv = (Fm – Fo), and Fm and Fo are maximum and minimum chlorophyll fluorescence, respectively, has been widely used to follow the seasonal acclimation of
PSII, because it is measured in dark-acclimated leaves. Seasonal changes in Fv/Fm can be caused by adjustments in either the photochemical capacity in PSII, or the capacity of thermal dissipation in PSII,
or both. However, there is a lack of chlorophyll fluorescence parameters that can distinguish between these processes. In
this study, we introduce two new parameters: the rate constants of sustained thermal energy dissipation (kNPQ) and of photochemistry (kP). We estimated kNPQ and kP from dark-acclimated Fo and Fm measured during spring recovery of photosynthesis in Scots pine (Pinus sylvestris L.) trees. We suggest that kNPQ and kP be used to study the mechanisms underlying the observed seasonal acclimation in PSII, because these parameters provide quantitative
data that complement and extend Fv/Fm measurements.
Keywords:
chlorophyll concentration, chlorophyll fluorescence, energy partitioning, Scots pine.
