Abstract: We used fast chlorophyll fluorescence transients (OJIP) to study provenance-related differences in photosynthetic performance and the magnitude of day-to-day chlorophyll fluorescence (ChlF) variation in northern (67° N) and southern (62° N) silver birches in a common garden at 62° N. ChlF transients were measured five times during two weeks in the middle of summer to avoid seasonal variation. Differences in growth and leaf morphological traits between the provenances were also examined. The northern trees had higher chlorophyll content, larger leaf areas, and higher leaf fresh and dry mass than the southern trees, but the leaf mass per area did not differ between the provenances. The southern trees were taller and showed higher annual shoot growth than the northern trees. For all the ChlF parameters, day-to-day variation was significant and followed the same pattern for both provenances with no significant provenance × day interaction, suggesting a similar response to environmental variation. The northern provenance had higher values in parameters related to the reduction of end electron acceptors at the Photosystem I (PSI) acceptor side as probed by ChlF. This and higher values for performance indices PIabs and PItot in northern than in southern trees suggest higher photosynthetic performance of northern trees in line with the latitudinal compensation strategy. Provenance differences in these parameters increased towards the end of the measurement period, suggesting preparation for earlier growth cessation in northern trees triggered by the shortening day length. The study shows that provenance differences in ChlF can be relatively stable regardless of environmental variation but might be influenced by physiological alterations in preparation for future changes in environmental conditions.

Key words: JIP test,  , Betula pendula, Provenances, Intra annual variation, Chlorophyll, Leaf mass per area, LMA, Growth