The Effect of Temperature and Light on Metrosideros polymorpha Seed Germination

Abstract

Seeds of a Hawaiian rain forest tree species, Metrosideros polymorpha, were germinated at temperatures ranging from 5 to 35°C and under photosynthetic photon flux densities ranging from 0 to approximately 2000 IlE·m-2·s-1. Results after 30 days indicate that 25°C is the optimal temperature and 170 IlE·m-2·s-1 or about 4-15 percent relative irradiance is the optimal light intensity for Metrosideros germination. Declining germination at higher irradiances was probably due to excessively high temperatures and intermittent desiccation. No seeds germinated at temperatures less than 12°C. Light was not found to be strictly required but improved germination by up to four times. Only 14 percent ofthe seeds sampled appeared to have intact embryos, hence the poor (15 percent) germination achieved even under optimal conditions. Low temperatures (generally less than 17°C) must curtail germination success on the floor of montane rain forests. The higher temperatures associated with increased light intensity are probably more beneficial than light itself in increasing germination success in forest clearings. These relationships to light and temperature may partly explain why Metrosideros seedlings are often infrequent beneath dense rain forest canopies.