Effect of high temperature on germination of four legumes from a forest-grassland mosaic in Southern Brazil

Abstract

Passage of a fire can break dormancy of the seeds of many plant species in fire-prone ecosystems. This response to fire is especially well known for the Fabaceae family, but has been poorly studied in Southern Brazil. We collected seeds of four Fabaceae species present in grasslands-forest mosaics of Southern Brazil: Mimosa bimucronata, Desmodium barbatum, Sesbania virgata and Collaea stenophylla. Seeds were exposed to different heat treatments (exposure to 60° and 80 °C for 5 minutes, to 100 °C for 2 minutes, control without heat treatment); not all species were tested in all treatments. After the treatment, the seeds were kept in a germination chamber with a light period of 12/12 hours and temperature of 25 °C. Germinated seeds were counted every 2 days. The results were analyzed by randomization testing. Germination of D. barbatum and S. virgata was increased after exposure to high temperatures (80° and 60 °C, respectively), while M. bimucronata showed reduced germination after temperatures of 80 °C and C. stenophylla no response. This study is the first for Southern Brazil to show a positive response of germination for grassland species exposed to high temperatures, simulating fire effects. As the study presented distinct responses of species to the heat treatment, it seems important to conduct more works with other species from the family, in order to be able to detect more general patterns.