Effect of Photoperiod on Annual Growth Cycle of Two forest Tree Species at Seedling Stage

Abstract

The seedlings of Pterygota alata and Manilkara bojeri were exposed daily to normal day length (ND), short day (SD) and long day (LD) conditions. Relative rates of extension growth were calculated under each treatment. Under ND conditions, Pterygota plants assumed dormant condition from November to March with major part of season's growth occurring in August-September. Manilkara plants under similar conditions, continued to grow though the growth rates declined progressively and were of lower order during December-January. Under LD treatment, Pterygota plants became dormant one month later and resumed growth about two months earlier than ND plants; SD conditions, however, brought about dormant growth at the same time as ND treatment but the growth was resumed as under LD plants i.e. about two months earlier than ND. Manilkara plants were induced to dormant condition both under SD and LD treatments and the period corresponded exactly with small growth rates under ND conditions. It is concluded that these two species are by and large indifferent to LD and SD conditions and that the annual growth-cycle in nature is more under the changing influence of total sum of weather conditions rather than entirely on day lengths.