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

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Nội dung Text: 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 of foliar characteristics in Betula alleghaniensis Britton P. Bellefleur J.P. Simon 2 3 M. 1 Labrecque 4 S. Popovich 1 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, and 4 Centre de Foresterie des Laurentides, For6ts Canada, C.P. 3800, Ste-Foy, Qc, G1 V 4C7, Canada applied during one growth season, on the Introduction morphology and chlorophyll content of leaves developing during the following Several studies have shown that the mor- year. The study was conducted with re- phology and physiological processes of forestation in mind and takes into account leaves are largely influenced by light the problem of changes in light conditions conditions in the environment. However, which seedlings grown in the nursery for 1 little 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 following spring. A few researchers have reported contradictory information. Isanogle (1944), Cormack and Gorham (1953) and, more Materials and Methods recently, Goulet and Bellefleur (1986) found that light intensity before leaf expan- During one growth season (n), 50 seedlings of sion 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 sun was not predetermined in the bud. Other (FSC), while 50 others were shaded condition reports concluded that the anatomical to receive 25% of full daylight (SC). Be- so as and physiological characteristics of early fore the of the following growth beginning sea- 1seedlings from each group were (n son leaves (preformed in the winter buds, + split into 2 lots so as to constitute 4 types of which emerge shortly after bud break) are treatments as shown in Table I. Early and late primarily determined by the light condi- leaf samples were harvested randomly from the tions prevailing during the previous growth seedlings during year n + 1. Early leaves were taken from the basis of long shoots, 1 and 4 wk season (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 and mine 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 previous sample: 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 stereological procedure similar to that used by Chabot and Chabot (1977)); and 3) chlorophyll content (a + b), expressed on the Leaf anatomy basis of leaf area and dry weight. All data were subjected to variance analysis, quoted signifi- at P:50.05. levels Table III summarizes data on anatomical cance are features. The method we used allowed comparison of the percentages of tissue volumes and air spaces in the leaf Results samples. In ec!rty leaves, palisade tissue and, to a greater extent, the volume of air spaces seem to have been most affected Leaf structure by changes in the light conditions. For treatments 1 and 3 (Table I), leaves had SLA values calculated for early and late proportionally more palisade tissue and leaves which developed during year n + 1 fewer air spaces than those subjected to are given in Table II. They were generally treatments 2 and 4 (Tables I and III). The higher for leaves which developed in full spongy mesophyll exhibited few variations with respect to the various treatments. A sun. However, under each type of experi- , ...... , .......
larger proportion of air spaces was also leaves the following spring. The conse- observed in late leaf samples harvested in quences on anatomy and, notably, on early July on seedlings of treatments 2 number of air spaces are evident. Further- and 4, but these differences were not more, this explains why specific leaf area observed in leaves harvested in mid- for seedlings grown under shade condi- tions during year n were not as important. August. Our results coincide with those of Roy et al. (1986) but are not inconsistent with Chlorophyll content those of Goulet and Bellefleur (1986) and Cormack and Gorham (1953), since we demonstrate that, as the season pro- chlorophyll content of early leaves The gressed, the e;arly leaves were more and also influenced by the light conditions was more influenced by the light conditions in of year n (Fig. 1For the 1 st harvest of their new environment. Similarly, late early leaves, the highest values, especial- leaves seemed to be influenced only by ly when expressed on the basis of dry current year light conditions. weight, were found in leaves harvested on seedlings of treatments 2 and 4. Dif- ferences were less noticeable in early leaves harvested later, and were no longer Acknowledgments significant in late leaves. We thank Chantal Martin for her technical assistance. This project was supported by the GRDE of Canada. Discussion All analyzed characteristics (structure, References anatomy and chlorophyll content) agree and demonstrate that the light conditions to which plants have been exposed have Chabot B.F. & Chabot J.F. (1977) Effects of light an influence on the development of early and temperature on leaf anatomy and photo-
synthesis in Fragaria Plant. 12, der buche, Fagus sylvatica. Physiol. Oecologia (Berlin) vesca. 545-550 26, 363-377 Cormack R.G.H. & Gorham A.L. (1953) Effects lsanogle LT. (1944) Effects of controlled shad- of exposure to direct sunlight upon the develop- ing upon the development of leaf structure in ment of leaf structure of two deciduous shrub 404- two deciduous tree species. Ecology 25, species. Can. J. Bot 31, 537-541 413 Goulet F. & Bellefleur P. (1986) Leaf morphology Roy J., Thiebaut B. & Watson M.A. (1986) Phy- plasticity in response to light environment in de- siological and anatomical consequences of ciduous tree species and its implication on forest morphogenetic polymorphism: leaf response to succession. Can. J. For. Res. 16, 1192-1195 light intensity in young beech trees (Fagus syl- vatica L.). Coll. lnt. sur IArbre, 9-14 Sept. Hansen H.C. (1959) Der einfluss des litchtes 1985, Montpellier. Nat Monsp. H.S. 431-449 auf die bildung von licht und schattenblattern