Effects of Smoke and Fire-related Cues on Penstemon barbatus Seeds

Abstract

Previous research has found that exposure to fire-related cues enhances germination of some plant species, and such species may exist in frequent-fire southwestern United States Pinus ponderosa forests. I performed four greenhouse experiments with Penstemon barbatus, a perennial forb common in P. ponderosa forests, testing seed responses to liquid and air smoke, charred P. ponderosa wood and leachate, heat and emergence substrates. Liquid smoke increased P. barbatus emergence to as high as 63%, 44% greater than controls, and enhanced emergence in all 4 experiments. Air smoke produced by burning P. ponderosa litter for 15 min appeared to increase emergence similar to liquid smoke. In contrast, P. ponderosa charred wood and charred wood leachate did not improve emergence, and sometimes inhibited positive effects of smoke. Heating samples at 100 C for 30 min did not affect emergence. Substrate and liquid smoke interacted in one experiment, with smoke increasing emergence more sharply on basalt and potting soil than on limestone soil. These greenhouse findings have practical implications for germinating P. barbatus, but need testing under field conditions to evaluate their importance in this species' population biology after fire in P. ponderosa forests.