Data from: Fire and summer temperatures interact to shape seed dormancy thresholds

Data for the following paper: Zomer M, Moreira B, Pausas JG. Fire and summer temperatures interact to shape seed dormancy thresholds. Annals of Botany <br><br>It includes 3 files in ASCII format: readme file, and two data files.<br>Abstract<br>In Mediterranean ecosystems, the heat shock of wildfire disrupts physical seed dormancy in many plant species. This triggers germination in the post-fire environment where seedling establishment is optimal due to decreased competition and increased resource availability. However, to maintain the soil seedbank until a fire occurs, the minimum heat capable of breaking seed dormancy (i.e., the lower heat threshold) must be above the maximum temperatures typically observed in the soil during the summer. We therefore hypothesized that summer temperatures have shaped heat requirements for physical dormancy release. Specifically, we predicted that seeds from populations growing under warmer summers will have higher values of the lower heat threshold.To evaluate this prediction, we collected seeds from two Cistus species in 31 populations (20 Cistus albidus; 11 Cistus salviifolius) along a climate gradient of summer temperatures on the eastern coast of Spain. For each population, seeds were treated to 10-minute heat shocks, from 30°C to 120°C in 5-degree increments (19 treatments), to simulate increasing heat doses from summer to fire-related temperatures. Seeds were then germinated in the lab. For all populations, maximum germination was observed when applying temperatures associated with fire. Lower heat thresholds varied among-populations, with a positive relation between summer temperatures at seed population origin and the heat dose required to break dormancy. Our results suggest that fire drives maximum dormancy release for successful post-fire germination, while summer temperatures determine lower heat thresholds for ensuring inter-fire seed bank persistence. Significant among-population variation of thresholds also suggests that post-fire seeder species have some potential to modify their dormancy-breaking requirements in response to changing climate.<br>