Báo cáo lâm nghiệp: Influence of light conditions on the predetermination of foliar characteristics in Betula alleghaniensis Britton

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Báo cáo lâm nghiệp: "Influence of light conditions on the predetermination of foliar characteristics in Betula alleghaniensis Britton"Influence of light conditions on the predetermination offoliar characteristics in Betula alleghaniensis Britton P. Bellefleur J.P. Simon 2 3M. 1 Labrecque 4 S. Popovich1 Jardin Botanique de la Ville de Montréal, 4101 est, rue Sherbrooke, Montréal, Qc, H 1X 2B2,2 Facult6 de Foresterie et G6od6sie, Universit6 Laval, Ste-Foy, Qc, G1K 7P4,3 D6partement des Sciences Biologiques, Université de Montr6al, Montr6al, Qc, H3C 3J7, and4 Centre de Foresterie des Laurentides, For6ts Canada, C.P. 3800, Ste-Foy, Qc, G1 V 4C7, Canada applied during one growth season, on theIntroduction morphology and chlorophyll content of leaves developing during the followingSeveral studies have shown that the mor- year. The study was conducted with re-phology and physiological processes of forestation in mind and takes into accountleaves are largely influenced by light the problem of changes in light conditionsconditions in the environment. However, which seedlings grown in the nursery for 1little is known about the importance of light or 2 seasons are subjected to when plant-conditions during the previous year on the ed.development of leaves the followingspring. A few researchers have reportedcontradictory information. Isanogle (1944),Cormack and Gorham (1953) and, more Materials and Methodsrecently, Goulet and Bellefleur (1986)found that light intensity before leaf expan- During one growth season (n), 50 seedlings ofsion was not important in determining leaf yellow birch (Betula alleghaniensis Britton) (1 +characteristics and that leaf expression 0) were grown outdoors in 1I pots in full sunwas not predetermined in the bud. Other (FSC), while 50 others were shaded conditionreports concluded that the anatomical to receive 25% of full daylight (SC). Be- so asand physiological characteristics of early fore the of the following growth beginning sea- 1seedlings from each group were (n sonleaves (preformed in the winter buds, + split into 2 lots so as to constitute 4 types ofwhich emerge shortly after bud break) are treatments as shown in Table I. Early and lateprimarily determined by the light condi- leaf samples were harvested randomly from thetions prevailing during the previous growth seedlings during year n + 1. Early leaves were taken from the basis of long shoots, 1 and 4 wkseason (Hansen, 1959; Roy et al., 1986). after leafing-out. New fully expanded late The objective of this study was to deter- leaves were harvested twice, early in July andmine the effect of various light treatments in mid-August. mental condition during year n + 1, a clear influence of the light treatment of the pre- vious year (n,l was observed. Under the same conditions, SLA values were signifi- cantly different for early leaves harvested at the beginning of the season. Leaves which developed on seedlings which were exposed to full sun conditions during year n had proportionally higher values than those grown in shaded conditions during year n. Differences exhibited by early leaves subsidetd a little as the growth sea- son progressed but can still be observed after 4 wk (Table II). In late leaves, the The following data were compared for each influence of light conditions of the previoussample: 1) specific leaf area (SLA, mg of dry year was not observed (Table II).weight per cm 2) proportion of leaf tissue ); 2(using a st ...