Requerimentos de luz e temperatura para a germinação de sementes de Aechmea nudicaulis (L.) Griesebach e Streptocalyx floribundus (Martius ex Schultes F.) mez (Bromeliaceae)

Abstract

Seeds of A. nudicaulis and S. floribundus were collected in a restinga located at Presidente Kennedy (ES, Brazil). This sandy community is characterized by the presence of patches of vegetation interspersed by open areas with a sparse plant covering. In order to evaluate the capacity of A. nudicaulis and S. floribundus to recruit individuals from seeds in the distinct microclimates generated by this heterogeneous plant covering, experiments were conducted in laboratory to test the effects of light and temperature on the germination for both species. Seeds of A. nudicaulis were unable to germinate in darkness but they achieved high germinability (≥90%) from 15 to 40°C under red light. Seeds of S. floribundus germinated in darkness only at 40ºC (22.5%), whereas the germinability was high (≥90%) from 15 to 30ºC under light. For both species, the germination rate was highest at 25ºC. For these bromeliads, alternating temperature (20/30ºC) promoted high germinability (≥92.5%) only under red light. The seeds at 20/30°C in darkness were later transferred to light and a high germinability (>89%) was achieved for both species. No seed germinated at alternating temperatures of 20/50ºC and they were dead after 720h of incubation. The seeds showed to be photoblastic and did not tolerate high temperatures. The results suggest that under natural conditions the germination of seeds of A. nudicaulis and S. floribundus is restricted to microclimates where light and moderate temperatures are present. The microsites generated by the plant covering seem to provide these requirements.