Effect of simulated parent-created microenvironmental condicions on germination of Retama sphaerocarpa (L.) Bois. Seeds.

Parent plants of woody species can créate special microenvironmental conditions in their neighbourhood that modify factors such as light intensity, litter accumulation or nutrient levéis. These conditions may be beneficial or not for their seeds to germinate, depending on trie species strategy. As a N-fixing species, Retama sphaerocarpa can exert its influence on soil nitrogen levéis as well as over light intensity. Moreover, adult plants understorey constitute a refuge for many herbaceous species, which can strong-ly compete with recently-established R. sphaerocarpa seedlings. Our objective was to test if the effect of parent-created microen-vironment is positive for R. sphaerocarpa seed germination under different meteorological conditions. Previously scarified seeds were used for the experiment, set to germinate in two different phytotrons, at 14°C and 19°C (simulating temperature conditions of early and late arrival of autumn rains), under full light and shade, and with three levéis of KN03. All factors considered (tem¬perature, light intensity and nitrate levéis) had significant effects in both final germination percentage and germination speed. The results seem to confirm our initial hypothesis about the favourable conditions provided by parent plants for R. sphaerocarpa seeds' germination. The effects on germination speed suggest that, under adult plant canopies, seedlings could have at least an initial advantage in their competition with seedlings of herbaceous species of the understorey, and the interactive effect between light and nitrate points to a colonisation strategy of open zones for this species