Protected from fire, but not from harm: seedling emergence of savanna grasses is constrained by burial depth

摘要

Background: The Cerrado is a fire-prone Neotropical savanna and grass seeds are the main component of the soil seed bank. Although grass seeds are presumed to tolerate heat pulses during fires, the assumption that these seeds will be recruited may be an overestimation, since it does not account for factors that limit seedling emergence from the soil. Aims: We tested if burial depth constrained the seedling emergence of nine common Neotropical savanna grasses. Methods: Seeds were sown at the surface or at 5, 10, 20 and 30 mm in trays filled with cerrado soil. Emergence was assessed daily for 30 days and any remaining non-germinated seeds were tested for viability. Results: Seedling emergence decreased with depth, and was positively related to the seed mass. Seven species showed a significant reduction in emergence when sown at 10 mm and only two species emerged from 30 mm. Most non-germinated seeds lost viability after 30 days. Conclusions: Burial depth constrained the seedling emergence of Neotropical savanna grasses. Although seeds in the soil are protected during Cerrado fires, they may not generate new individuals, as seedling emergence is limited once a depth of 10 mm is reached and the seeds lose viability within 30 days in humid soil.