© 2005 Heron Publishing—Victoria, Canada
Regeneration patterns in boreal Scots pine glades linked to cold-induced photoinhibition
Martijn Slot (1, 2, 3), Christian Wirth (1, 4), Jens Schumacher (1), Godefridus M. J. Mohren (2), Olga Shibistova (5), Jon Lloyd (1, 6) and Ingo Ensminger (1, 7, 8)
1. Max Planck Institute for Biogeochemistry, Hans-Knöll-Strasse 10, 07745 Jena, Germany / 2. Forest Ecology and Forest Management Group, Wageningen University, P.O. Box 342, 6700 AH, Wageningen, The Netherlands / 3. Resource Ecology Group, Wageningen University, Bornsesteeg 69, 6708 PD Wageningen, The Netherlands / 4. Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA / 5. Institute of Forests, Russian Academy of Sciences, Siberian Branch, Akademgorodok, 660036 Krasnoyarsk, Russia / 6. School of Geography, University of Leeds, Leeds, LS2 9JT, UK / 7. Corresponding author (iensming@uwo.ca) / 8. Department of Biology and The BIOTRON, University of Western Ontario, London, ON N6A 5B7, Canada / Received September 15, 2004; accepted February 18, 2005; published online July 4, 2005
Summary
Regeneration patterns of Pinus sylvestris L. juveniles in central Siberian glades were studied in relation to cold-induced photoinhibition. Spatial distribution of
seedlings in different height classes revealed higher seedling densities beneath the canopy than beyond the canopy, and significantly
higher densities of seedlings < 50 cm tall on the north side of the trees. These patterns coincided with differences in light
conditions. Compared with plants on the north side of canopy trees (north-exposed), photosynthetic photon flux (PPF) received
by plants on the south side of canopy trees (south-exposed) was always higher, making south-exposed plants more susceptible
to photoinhibition, especially on cool mornings. Chlorophyll fluorescence data revealed lower photochemical efficiency and
increased non-photochemical quenching of small (20–50 cm in height), south-exposed seedlings from spring to early autumn,
indicating increased excitation pressure on photosynthesis. Maximum rate of oxygen evolution was less in south-exposed plants
than in north-exposed plants. Increased pools of xanthophyll cycle pigments and formation of the photoprotective zeaxanthin
provided further evidence for the higher susceptibility to photoinhibition of south-exposed seedlings. A linear mixed model
analysis explained many of the physiological differences observed in seedlings according to height class and aspect with early
morning temperature and PPF as predictors. The link between photoinhibition and differential distribution of seedlings by
height class suggests that photoinhibition, together with other environmental stresses, decreases the survival of small, south-exposed
P. sylvestris seedlings, thereby significantly affecting the regeneration pattern of central Siberian pine glades.
Keywords:
environmental stress, excitation pressure, Pinus sylvestris, Siberia, xanthophyll cycle.
