Annual cycle of photosynthetic capacity
Coniferous trees growing in the boreal and temperate zones have a clear annual cycle of photosynthetic activity.

The rate of photosynthesis is low or zero during winter, increases during spring, peaks during summer and decreases during autumn. Part of this cycle can be explained by direct responses to photosynthetically active radiation (PAR) and air temperature. Hari and Mäkelä (2003) 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 showed, 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. 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.


Hari, P. and Mäkelä, A. 2003. Annual pattern of photosynthesis of Scots pine in the boreal zone. Tree Physiology 23, 145-155.

Kolari, P., Lappalainen, H.K., Hänninen, H. & Hari, P. 2007. Relationship between temperature and the seasonal course of photosynthesis in Scots pine at northern timberline and in southern boreal zone. Tellus 59B, 542–552.

Mäkelä, A., Hari, P., Berninger, F., Hänninen, H. & Nikinmaa, E. 2004. Acclimation of photosynthetic capacity in Scots pine to the annual cycle of temperature. Tree Physiology 24, 369-376.