Seed functional ecology in Brazilian rock outcrop vegetation: an integrative synthesis

Abstract

ABSTRACTBackground and AimsRock outcrop vegetation is distributed worldwide and hosts a diverse, specialised, and unique flora that evolved under extremely harsh environmental conditions. Unfortunately, seed ecology in such ecosystems has received little attention, especially regarding the association between seed traits, germination responses and adult plant ecology. Here, we provide a quantitative and phylogenetically-informed review of the seed functional ecology of Brazilian rocky outcrop vegetation, focusing on four vegetation types:campo rupestre,canga,campo de altitudeand inselbergs.MethodsUsing a database with functional trait data for 383 taxa and 10,187 germination records for 281 taxa, we calculated the phylogenetic signal of seven seed traits and tested whether they varied among growth forms, geographic distributions, and microhabitats. We also conducted meta-analyses to understand the effects of light, temperature, and fire-related cues on the germination ofcampo rupestrespecies and how the beforementioned ecological groups and seed mass affect such responses.Key ResultsAll traits showed a strong phylogenetic signal.Campo rupestrespecies responded positively to light and had their maximum germination between 20-30°C. The effect of temperatures below and above this range was modulated by growth form, with shrubs requiring and tolerating higher temperatures to germinate. We only found evidence of a moderating effect of seed mass for responses to heat shocks, with larger, dormant seeds better tolerating heat.Seeds exposed to heat shocks above 200° C lost viability, whereas smoke accelerated germination. No consistent differences in germination responses were found between restricted or widespread species or microhabitats. However, species from xeric habitats evolved phenological strategies to synchronise germination during periods of higher soil water availability.ConclusionsPhylogenetic relatedness plays a major role in the seed ecology of Brazilian rock outcrop vegetation. However, seed traits and germination responses did not explain species’ geographic distribution and microhabitat differentiation, suggesting other traits are more likely to explain such differences.