EFFECTS OF LIGHT AND TEMPERATURE ON GROWTH OF GINKGO-BILOBA 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-degrees-C, 16 h day length in small climate chambers at either 24-17-degrees-C, with 16 h of 250 or 430-mu-E.m-2.s-1 for 40 wk or at 32-35-degrees-C, with 16 h of 250-mu-E.m-2.s-1 for 20 wk (due to the limited height of the climate chambers). Table I showed the heterogenous growth of plants in relation to environmental conditions. At 24-17-degrees-C, under natural light or moderate artificial light (250-mu-E.m-2.s-1), Ginkgo plants completed 1 or 2 growth cycles, corresponding to 1 or 2 shoots. Under high energy light (430-mu-E.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-degrees-C), each growth period of a maximum duration of 10 wk ended in a rest period. At high temperatures (32-25-degrees-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-degrees-C, the main stem extension was enhanced by artificial light of 250-mu-E.m-2.s-1 and inhibited by artificial light of 430-mu-E.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-degrees-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-degrees-C was similar to the profile of a 2-shoot plant grown at 24-17-degrees-C, 430-mu-E.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-degrees-C or 32-25-degrees-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.