Photo- and thermoperiodic responses of different larch provenances (Larix decidua Mill.)
The present investigation was undertaken in order to study the formation of the terminal buds, top shoot maturation, bud break and flushing as well as the amount of growth of the top shoot under different photo- and thermoperiodic conditions, in three larch provenances (Larix decidua Mill.). Two-year-old plants were tested under long- (LD = 16 h) and short-day (SD = S h) conditions and under various temperature combinations. The experiment went on for 59 weeks in a phytotron. The plants' growth activities were greatest under LD conditions. SD conditions were necessary for the plants to complete their vegetative growth. For bud formation and lignification of the leading shoot, relatively high temperatures were required under SD conditions. Under low temperatures, bud formation was incomplete and the leading shoot remained unlignified. The investigation showed that there is an interaction between photo- and thermo-period which determines the plants' vegetative cycle. In comparison with the climate of the place of origin of the larch, in northern Scandinavia the days are longer and the temperatures lower in the autumn. This is the reason why the introduced larch hardens poorly and too late, which in its turn makes it sensitive to early frosts.
photoperiodic responses; termoperiodic responses; Larix
Studia Forestalia Suecica
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