Environmental factors influencing fruit production and seed biology of the critically endangered Persoonia pauciflora (Proteaceae)

Abstract

The factors that influence seed production and seed dormancy in rare plant species are crucial to their conservation yet are often poorly understood. In this study, we examined the breeding system and seed biology of the critically endangered Australian endemic species Persoonia pauciflora through a series of experiments. Pollinator visitation surveys and manipulative hand-pollination treatments were conducted to investigate the breeding system and subsequent seed production. We used an experimental seed burial to examine the breakdown of the woody endocarp and changes to germination over time. Seed germination response under simulated local seasonal conditions was also examined. Persoonia pauciflora was found to be predominantly pollinated by native bees, and cross-pollinated flowers produced significantly more mature fruit (18 ± 3%) than self-pollination treatments (2–3%). The average strength of P. pauciflora pyrenes buried in soil significantly decreased over two years, from 413.3 ± 14.6 N to 130.8 ± 11.8 N. Post-burial seed germination was cyclical, with highest final germination percentage occurring following late-summer exhumations (75 ± 2% and 74 ± 14%, respectively). When seeds were incubated under different local seasonal conditions, germination at local summer temperatures was more likely when compared with autumn/spring and winter temperature-incubated seeds. Our study highlights the importance of ensuring appropriate biotic pollen vectors are present in the local landscape for maximising viable fruit production for this species. In addition, our data indicate that recruitment will most likely occur after the endocarp has suitably weakened, allowing physiological dormancy of the embryo to be relaxed and germination to commence following summer temperatures.