Daylength Responses of some Forest Trees
Acta botanica neerlandica , Volume 4 - Issue 5 p. 657- 670
The influence of daylength has been investigated on some aspects of vegetative growth in tree seedlings. With Liriodendron and Fagus greenhouse experiments were carried out. Natural daylight was used for the basic illumination period of 10 hours, extended by light of fluorescent tubes to a daylength of 16 hours, when necessary. In both species long day brings about a lengthening of branches, in Liriodendron especially of the main shoot, and a higher fresh and dry weight. A daylength of 16 hours did not cause continuous growth during winter under the conditions of our experiments and with the provenances we used, as is found by Garner and Allard (1923) and Kramer (1936). Yet it brought about a lengthening of the growth period in both species, as compared with a daylength of 10 hours. Winterrest begins much later and ends somewhat earlier under long day treatment. For two provenances of Pinus silvestris, from Sweden (more than 66° N.L.) and from France (45° 30' N.L.) the possible interaction between effects of racial variety and daylength have been studied. Plants of southern provenance, normally growing in relatively short days, grew very well in long days (24 hours) as well as in short days (12 hours), in both cases forming well-developed shoots and having a normal green colour. Plants of northern provenance grew very well in long days but badly in short days, here showing badly developed shoots and a bad colour. Seedlings of southern provenance showed a positive correlation between growth and relative size of the root system, except in special cases (development of mycorrhiza?), for plants of northern provenance such correlation was not observed. The main data collected are shown in Table 9.
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