Plant sexual reproduction is influenced by fire frequency: evidence from a resprouting herb in Chaco ecosystems

Reduced competition and increased availability of abiotic resources shortly after a fire can favour growth and flowering of herbaceous species. These changes may also affect the pollinator community, reproductive success, and, potentially, the characteristics of progeny. However, anthropogenic increases in the frequency of fires could reverse the beneficial effects of fire. We evaluate the effect of fire frequency on sexual expression, pollination, female reproductive success, and early progeny vigour of Solanum palinacanthum, an andromonoecious resprouting herb in South American Chaco ecosystems. Measurements were performed at six sites along a gradient of fire frequency, ranging from 0 to 5 fires over 22 years. We found that plant size and the proportion of hermaphrodite (relative to male) flowers increased at intermediate fire frequency sites (twice burned) compared to unburned sites, but both declined at high-fire frequency sites. Pollinator visits were also more frequent in plants from the area with intermediate fire frequency. Although fire frequency did not enhance the probability of fruit set, it increased total fruit number in plants from the site burned twice. Seeds from sites with intermediate fire frequency had both higher mass and germination rates. Soil resources and maternal environmental effects shaped by fire frequency play a key role in the sexual reproduction and early progeny vigour of S. palinacanthum. Nonetheless, increased fire frequency due to human activities may override the beneficial effects of fire on plant reproduction.