Wide variation in post-emergence desiccation tolerance of seedlings of fynbos proteoid shrubs

AbstractFynbos Proteaceae that are killed by fire and bear their seeds in serotinous cones (proteoids), are entirely dependent on seedling recruitment for persistence. Hence, the regeneration phase represents a vulnerable stage of the plant life cycle. In laboratory-based experiments we investigated the effect of desiccation on the survival of newly emerged seedlings of 23 proteoid species (Leucadendron and Protea) occurring in a wide variety of fynbos habitats. We tested the hypothesis that species of drier habitats would be more tolerant of desiccation than those from more moist areas. Results showed that with no desiccation treatment, or with desiccation prior to radicle emergence, all species germinated to high levels. However, with desiccation treatments imposed after radicle emergence, there were significant declines in seedling emergence after subsequent re-wetting. Furthermore, other than three species that grow in waterlogged habitats, germination responses could not be reliably modeled as a function of soil moisture variables. An important finding was that the species had highly individualistic responses to desiccation. In conclusion, early seedling emergence represents a species-specific stage that is highly sensitive to a decrease in soil moisture. Since species are killed by fire (non-sprouting), vulnerability to increasing aridity associated with anthropomorphic climate change would increase the odds of local and global extinction