Are wildfires affecting seed germination in cactus? An experimental assessment

Abstract

Cacti are conspicuous plants across arid and semi-arid ecosystems of the American continent and are currently under threat due to human pressures, such as habitat loss, illegal collection and changes in fire regimes. Although much of their habitat is highly fire prone, there are strikingly few studies on their germination response to fire cues. The aim of this work was to analyse the effect of heat shock (simulating wildfires) on the ‘germination %’ and the ‘mean germination time’ of 13 cactus species of two growth forms (six columnar and seven globose) from a fire-prone cactus diversity hotspot in Córdoba Mountains, central Argentina. We also analysed the effect of growth form and seed mass on species responses. Seeds were subjected to the following treatments: 70°C/5 min, 70°C/10 min, 105°C/5 min, 105°C/10 min and a control (i.e. no heat). Germination decreased under at least one treatment in seven species, increased in three species, had contrasting changes in one species, and showed no effect of treatments in two species. Germination was faster in eight species, slower in one species and showed no effects of treatments in four species. Germination was significantly higher for globose species following the 70°C/10 min treatment and for columnar species under the treatment of 110°C/10 min; while germination time did not differ between growth forms. Seed mass did not have a significant effect on germination, and only affected germination time under the 70ºC treatments, under which lighter seeds germinated faster than heavier seeds. Our results show that the studied species exhibited a high diversity of responses, with most of the species presenting tolerance to heat shock, and that under certain conditions growth form and seed mass are important traits related to species responses to heat shock treatments.