Comparative Eco-Physiology of Epilobium Hirsutum L. and Lythrum Salicaria L.: IV. Effects of Temperature and Inter-Specific Competition and Concluding Discussion

When Epilobium hirsutum and Lythrum salicaria were grown in controlled environmental cabinets, they produced similar dry weights and leaf areas per plant at 18°C. However, at 8°C, growth of L. salicaria was far more severely restricted, compared with that at 18°C, than was growth of Epilobium hirsutum. A controlled experiment in a glasshouse showed that Lythrum salicaria was more successful than Epilobium hirsutum in inter-specific competition both in standard and diluted nutrient solutions, at a constant temperature of 25°C. Field experiments in which seedlings were planted in soil of low fertility in early summer also showed Lythrum salicaria to be the more successful competitor. However, in a fertile fen soil and an experiment which included the low temperature conditions between autumn and spring, Epilobium hirsutum exerted a strong suppressive influence on the growth of Lythrum salicaria in the following summer. Results presented in this paper and previous ones in the series are discussed in relation to the geographical and ecological distributions of the species. Epilobium hirsutum can germinate and grow in low temperatures and short days and in these circumstances by virtue of its growth form and pattern of vegetative reproduction it rapidly exploits available space. Given higher temperatures, Lythrum salicaria survives and grows faster than Epilobium hirsutum on nutrient-deficient media and soils.