© 2004 Heron Publishing—Victoria, Canada
Acclimation of photosynthetic capacity in Scots pine to the annual cycle of temperature
Annikki Mäkelä (1, 2), Pertti Hari (1), Frank Berninger (1), Heikki Hänninen (3) and Eero Nikinmaa (1)
1. Department of Forest Ecology, P.O. Box 27, FIN-00014, University of Helsinki, Finland / 2. Corresponding author (annikki.makela@helsinki.fi) / 3. Department of Ecology and Systematics, P.O. Box 65, FIN-00014, University of Helsinki, Finland / Received June 9, 2003; accepted September 28, 2003; published online February 2, 2004
Summary
Coniferous trees growing in the boreal and temperate zones have a clear annual cycle of photosynthetic activity. A recent
study demonstrated that the seasonal variation in photosynthetic capacity of Scots pine (Pinus sylvestris L.) could be attributed mainly to the light response curve of photosynthesis. The magnitude of the light response curve varied
over the season while its shape remained constant, indicating that the two physiological parameters quantifying the curve—the
quantum yield per unit internal carbon dioxide concentration and the corresponding light-saturated rate—remained proportional
to each other. We now show, through modeling studies, that the quantum yield (and hence the light-saturated rate) is related
to the annual cycle of temperature through a delayed dynamic response. The proposed model was tested by comparing model results
with intensive measurements of photosynthesis and driving variables made from April to October in three shoots of Scots pine
growing near the northern timberline. Photosynthetic capacity showed considerable acclimation during the growing season. A
single model describing photosynthetic capacity as a reversible, first-order delay process driven by temperature explained
most of the variation in photosynthetic capacity during the year. The proposed model is simpler but no less accurate than
previous models of the annual cycle of photosynthetic capacity.
Keywords:
annual cycle, dynamic model, optimal stomatal control, shoot photosynthesis.
