Ann. For. Sci. 48 (1991) 133-147
DOI: 10.1051/forest:19910202

Influences de l'éclairement et de la température sur divers paramètres de croissance de jeunes Ginkgo biloba L cultivés en conditions contrôlées de jours longs

V Flesch^{a, b, c}, M Jacques^b, L Cosson^c, V Pétiard^d and JP Balz<sup>a

a</sup>  Institut H Beaufour, 17, avenue Descartes, 92350 Plessis-Robinson
^b  Université Paris VI, laboratoire de physiologie de développement des plantes, 4, place Jussieu, Tour 53, E5 75252 Paris cedex 05
^c  Université Paris XI, laboratoire de botanique et de phytochimie, avenue JB Clément, 92290 Châtenay-Malabry
^d  Francereco, 30-38, avenue G Eiffel, 37001 Tours, cedex, France

Résumé - La croissance végétative de jeunes Ginkgo biloba L a été étudiée en conditions contrôlées dans les serres et les enceintes climatisées du Phytotron à différentes températures et sous éclairements de longue durée (16 h) de qualité et de densité de flux quantique différentes. Cultivés en éclairement naturel ou en éclairement artificiel de 250 μE.m^-2.s^-1, à 24-17 °C, les plants effectuent 1 ou 2 cycles végétatifs selon les individus (tableau I). Aux mêmes températures, un éclairement de 430 μE.m^-2 .s^-1 favorise les reprises spontanées de croissance et permet à certains jeunes plants de réaliser 3 pousses. L'allongement caulinaire (fig 1), plus sensible aux variations de la lumière que l'émission foliaire (fig 2), est stimulé par un éclairement de 250 μE.m^-2.s^-1. Des températures élevées (32-25 °C) associées à un éclairement de 250 μE.m^-2.s^-1 maintiennent une majorité des plants en croissance active (fig 1 A) pendant une longue durée. Dans toutes les conditions (figs 3, 4, 5, 6), on retrouve une organisation périodique le long de l'axe principal (alternance de zones d'entrenoeuds longs et courts). L'agencement spatial des entrenoeuds n'est pas modifié par les facteurs de l'environnement, contrairement à l'agencement temporel accéléré aux températures élevées. Le développement des bourgeons axillaires en auxiblastes ou en brachyblastes est toujours limité (tableaux II, III). Il se produit au niveau des entrenoeuds longs (figs 3, 4, 5, 6).

Abstract - Effects of light and temperature on growth of Ginkgo blloba cultivated under controlled long day conditions. The vegetative growth of Ginkgo biloba L (Ginkgoaceae) at varying temperatures and under different types of light (natural or artificial) has been described. Young Ginkgo plants originating from Korean seeds were grown in Phytotron controlled greenhouses at 24-17 °C, 16 h day length in small climate chambers at either 24-17 °C, with 16 h of 250 or 430 μE.m^-2.s^-1 for 40 wk or at 32-35 °C, with 16 h of 250 μE.m^-2.s^-1 for 20 wk (due to the limited height of the climate chambers). Table / showed the heterogenous growth of plants in relation to environmental conditions. At 24-17 °C, under natural light or moderate artificial light (250 μE.m^-2.s^-1), Ginkgo plants completed 1 or 2 growth cycles, corresponding to 1 or 2 shoots. Under high energy light (430 μE.m^-2.s^-1) at the same temperature, we observed 3 successive growth cycles for some plants (figs 1C and 2C). At warm temperatures (24-17 °C), each growth period of a maximum duration of 10 wk ended in a rest period. At high temperatures (32-25 °C), the young Ginkgo plants were able to grow continuously for 20 wk. These temperatures enhanced both main stem elongation and young leaf emission on 1-shoot-plants (figs 1A, 2A). At 24-17 °C, the main stem extension was enhanced by artificial light of 250 μE.m^-2.s^{- 1} and inhibited by artificial light of 430 μE.m^-2.s^-1 (figs 1A, 1B). The production of leaves was less sensitive to quality and intensity of light than shoot growth. Plants with 1 shoot, cultivated under 3 variable light conditions at the same temperature produced the same number of leaves (fig 2A). Foliar emission was generally increased by an increase in temperature. In all cases, the main axis presented a periodic organization with alternately long and short internodes (figs 3-6). The first shoot generally had 2 long internodal sections whereas the following shoots only had one. Environmental conditions did not modify the sequence (spatial organization) of these internodal areas, but could increase or reduce the number and size of the internodes constituting these areas. At 32-25 °C, the plants presented more and longer internodes. High temperatures accelerated the arrangement of the internodal areas. At the 20th week, the profile of a young plant grown at 32-25 °C was similar to the profile of a 2-shoot plant grown at 24-17 °C, 430 μE.m^-2.s ^-1. for 40 wk (fig 4, plant No 83; fig 6, plant No 186). After bursting, axillary buds of Gingko biloba gave out short or long shoots (figs 3-6). Long shoots only presented 1 long internodal section. Ramification was influenced by the spectral quality of light and temperature (tables II, III). Most plants growing under artificial illumination at 24-17 °C or 32-25 °C had short or long shoots. Conversely, natural day light reduced bud reactivation and shoot development. Extension of long shoots, as well that of the main axis was enhanced by high temperatures.

Key words: Ginkgo biloba / growth / photon flux density / temperature / branching

Mots clés : Ginkgo biloba / croissance / densité de flux quantique / température / ramification