Seasonal acclimation of photosystem II in Pinus sylvestris. II. Using the rate constants of sustained thermal energy dissipation and photochemistry to study the effect of the light
environment
Albert Porcar-Castell (1, 2), Eija Juurola (1), Ingo Ensminger (3, 4), Frank Berninger (5), Pertti Hari (1) and Eero Nikinmaa (1)
1. Department of Forest Ecology, University of Helsinki, P.O. Box 27, 00014 Helsinki, Finland / 2. Corresponding author () / 3. Department of Biology and Biotron, University of Western Ontario, London, ON N6A 5B7, Canada / 4. Present address: Department of Forest Ecology, Forest Research Institute Baden-Wuerttemberg, 79100 Freiburg, Germany / 5. Département des sciences biologiques, Université du Québec à Montréal, CP 8888, succ. Centre-ville, Montreal, QC H3C 3P8,
Canada / Received September 10, 2007; accepted June 6, 2008; published online August 1, 2008
Summary
Photosynthesis in evergreen conifers is characterized by down-regulation in autumn and rapid up-regulation in spring. This
seasonal pattern is largely driven by temperature, but the light environment also plays a role. In overwintering Scots pine
(Pinus sylvestris L.) trees, PSII is less down-regulated and recovers faster from winter stress in shaded needles than in needles exposed to
full sunlight. Because the effect of light on the seasonal acclimation of PSII has not been quantitatively studied under field
conditions, we used the rate constants for sustained thermal energy dissipation and photochemistry to investigate the dynamics
and kinetics of the seasonal acclimation of PSII in needles exposed to different light environments. We monitored chlorophyll
fluorescence and needle pigment concentration during the winter and spring in Scots pine seedlings growing in the field in
different shading treatments, and within the crowns of mature trees. The results indicated that differences in acclimation
of PSII in overwintering Scots pine among needles exposed to different light environments can be chiefly attributed to sustained
thermal dissipation. We also present field evidence that zeaxanthin-facilitated thermal dissipation and aggregation of thylakoid
membrane proteins are key mechanisms in the regulation of sustained thermal dissipation in Scots pine trees in the field.
Keywords:
chlorophyll fluorescence, Scots pine, spring recovery, zeaxanthin.
