The seasonal changes in two of the photosynthetic parameters of Scots pine (Pinus sylvestris L.), i.e. the light-saturated assimilation rate (A max ) and the apparent quantum yield (a), were compared with the cold hardiness of needles throughout the course of a year. The data for the comparison were obtained from an experiment with close to ambient and elevated temperatures in opentop chambers. The cold hardiness correlated with the photosynthesis parameters, but the relation was different in the cold acclimation and deacclimation phases, i.e. the same cold hardiness corresponded differently with A max and a in the autumn and spring. The temperature treatment had a clear effect on the relation of a with cold hardiness in the dehardening phase but not during the hardening phase. The ecological significance of the seasonal changes in the photosynthetic capacity, i.e. in A max and a, is discussed.

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