Time since fire and soil depth shapes grass regeneration niche in Cerrado

Abstract

In savannas, fire triggers physical and chemical changes in the soil, releasing nutrients and other substances predicted to stimulate seed germination and plant growth. However, these effects and how changes along the soil profile can shape species regeneration niches after fire disturbances are still poorly understood. Here, we aimed to investigate (i) whether soil affected by fire alters grass emergence percentage, mean emergence time (MET), number of tillers, and shoot and root dry mass and (ii) how persistent these effects can be over time. We compared seedling emergence and plant growth of three native grasses in soil from Cerrado savannas soon after fire, 6 months after fire and unburned (long time since fire), at two depths (0–2 and 0–10 cm). No differences were found in emergence percentage, but MET was reduced by 42% in the soon after fire soil up to 2 cm, compared to unburned soils at 2 cm. MET was also reduced compared to unburned soils in 0–10 cm 6 months post-fire soil (from 7.5 to 6.4 days). Plants grew more in burned soils than those unburned, displaying greater above and belowground dry mass and more tillers. The effects of fire on plant growth in soils were transient, as plant growth responses in soils after 6 months post-fire were not significantly different from plant growth responses in the unburned soil, except for one species. Here, we add evidence that fire is an essential component in community assembly in savannas, specifically elucidating that it plays an important role in grass regeneration.