PARENT SESSION
Posters P3B Photosynthetic acclimation: Ecophysiology, diverse environments. Abstracts (479-522)

Can temperature-light-interactions explain site-specific differences of the spring recovery of photosynthesis in boreal Scots pine? Albert Porcar-Castell^*,1, Ingo Ensminger², Frank Berninger³, Eija Juurola¹, Eero Nikinmaa¹, Pertti Hari¹, ¹ University of Helsinki, Department of Forest Ecology, Helsinki, Finland² Max-Planck Institut für Biogeochemie, Hans-Knöll-Str. 10, Jena, Germany³ Département des Sciences Biologiques, Montréal, Canada

ABSTRACT- Energy imbalances between light and dark reactions are intense during spring in boreal conditions due to combination of low temperatures with high light, thereby boreal evergreens have evolved protective acclimation mechanisms to minimize the risks associated with these imbalances. One of the main mechanisms is the increase in the pool of xanthophyll-cycle pigments (VAZ) and in its de-epoxidation status (DEPS), which improve the dissipation of excess energy. Our aim is to identify differences in the pattern of cold acclimation and subsequent spring recovery of photosynthesis between two boreal Scots pine populations with similar latitude (same photoperiod) but contrasting climates (Finland and Siberia). We measured maximum quantum yields (F_v/F_m) by fluorometric techniques and collected needle samples throughout winter and spring in both sites. Data on VAZ and DEPS were obtained with HPLC. Micrometeorological data were used to link physiological processes with environmental parameters. Siberian and Finnish populations reached similar maximum DEPS values, however DEPS was not maximum in Finland until middle February whereas in Siberia values were already maximum since autumn. Decrease in DEPS started when temperatures went above zero degrees during the first week of April in Finland but not until the first week of May in Siberia. F_v/F_m reached lower values in Siberia compared to Finland, 0.039 and 0.138 respectively, and in both sites F_v/F_m recovered concomitantly with the decrease in DEPS. VAZ followed a similar pattern in both sites, increasing towards the end of the spring when a higher protection was needed and decreasing after that. Thus, dynamics of DEPS and VAZ seem to be important factors behind the cold acclimation and spring recovery of photosynthesis in boreal Scots pine. With respect to variations in land surface air temperature we discuss site-specific effects of these environmental changes on the commencement of spring photosynthesis in high latitudes.

KEY WORDS: Spring Recovery, Scots Pine, Xanthophyll Cycle