Flowering of Blandfordia grandiflora (Christmas bells) in response to fire frequency and temperature

Blandfordia grandiflora (Blandfordiaceae) is a resprouting perennial herb in wet heathland of coastal and tableland habitats on mainland eastern Australia. It has attractive turbinate flowers of considerable horticultural value. Blandfordia grandiflora is reported to have an enhanced flowering response in the first post-fire flowering season, and management prescriptions advocate frequent fire as beneficial for the species. Nonetheless, the present study appears to be the first to document the flowering response and fate of individual plants exposed to a range of fire frequencies (3-, 6- and 9-year intervals) over an extended period. We also examined the flowering response in unburnt habitat. High survival rates (>95%) were observed for B. grandiflora plants in heathland that had remained unburnt for a minimum of 30 years. Flowering after experimental burns was found to peak in the second post-fire flowering season rather than the first, and there was no clear fire frequency effect. Maximum levels of flowering during the second post-fire season reached 38 to 56% of individuals, although in some years post-fire flowering during this peak season was as low as 23%. Comparatively few plants flowered during the second-year peak season after every fire, and ~34% of individuals in both the 6- and 9-year burn treatments failed to flower at any time. Inter-fire flowering was also observed, and in some instances this flowering was not significantly different to the level achieved during the peak post-fire flowering season. For example, ~9% of individuals flowered 5–7 times over a 12-year period despite being burnt on only four occasions. Flowering after vernalisation (winter-chilling) was observed in unburnt heathland, and the level of this response was not significantly different to peak post-fire flowering in some years. The findings are examined in the context of evolutionary and habitat processes within a climate change framework. Future studies should focus on the complex interactions between climate, fire and soil for not only B. grandiflora, but more importantly for the diverse assemblage of plant species in wet heathland.

Breeding Systems of Disjunct Populations of Christmas Bells (Blandfordia grandiflora R.Br., Liliaceae): Variation in Self-Fertility and an Ovular Mechanism Regulating Self-Fertilisation

The breeding systems of disjunct tableland and coastal populations of Christmas bells were determined using hand-pollination experiments. In both populations, 90% or more of self-pollinated plants produced seeds. Tableland plants were significantly more self-fertile than coastal plants (ratio of self seed set to cross seed set: tableland, 0.55 ± 0.03; coast, 0.08 ± 0.02). Significant variation among plants for self-fertility was found in both populations. Autofertility was 1.6% or less in both populations indicating that pollen vectors are necessary for seed set. Seed set by agamospermy in both populations was less than 0.1%. Percentage seed abortion was greater in self-pollinated plants than cross-pollinated plants in both populations. In both self- and cross-pollinated plants, seed abortion was twice as great in the coastal population than in the tableland population. No evidence was found for stigmatic or stylar self-incompatibility. Self and cross pollen adhered to and germinated equally well on stigmas in both populations (72 - 77% germination). Similarly, there were no differences between pollination treatments or populations in the percentage of ovules penetrated by pollen tubes (82 - 89% penetration). When self-pollination preceded cross-pollination by 24 h or longer seed set was significantly reduced compared to flowers that were cross-pollinated only, suggesting ovules were pre-empted by self pollen tubes. Collectively these results strongly suggest that self seed set was reduced by a mechanism operating at the ovule level, such as early-acting inbreeding depression due to recessive seed-aborting genes, although incomplete late-acting self-incompatibility cannot be ruled out. For coastal plants, this ovular mechanism largely prevents selfing, indicating plants were predominantly outcrossing although most produced some self seed. For tableland plants, substantial seed set by selfing may occur under natural conditions.

Floral Morphology, Biology and Sex Allocation in Disjunct Populations of Christmas Bells (Blandfordia grandiflora, Liliaceae) With Different Breeding Systems

Evolutionary shifts in breeding systems are often accompanied by changes in reproductive attributes such as floral morphology and biology, and pre- and post-zygotic allocation patterns. The effects of breeding system variation on several such attributes were examined in self-fertile tableland and outcrossing coastal populations of Blandfordia grandiflora R. Br. In general, overall flower size was similar in both populations, although pedicel and pistil stipe diameters were greater in coastal plants, and pistil length and stigma-anther separation were greater in tableland plants. Although all floral parts from coastal flowers weighed more, proportional biomass allocation to floral parts was similar in both populations. Daily nectar production per flower was similar in both populations. Tableland flowers produced more ovules but fewer pollen grains than did coastal flowers. Pollen-ovule ratios were 11 500 in coastal flowers and 5600 in tableland flowers. Open-pollinated tableland fruits produced more seeds than coastal fruits, but individual seeds weighed less; total seed biomass of tableland fruits was greater than coastal fruits. Prezygotic relative male biomass did not differ significantly between populations. Relative male biomass, estimated from stamen and seed weights, was 5% greater in coastal plants, although populations did not differ significantly. Similarly, relative biomass allocation to pollinator attraction (i.e. coralla and nectar) did not differ between populations. The onset and duration of stigmatic receptivity and pollen longevity of flowers from the two populations were similar. The large differences in ovule, seed and pollen production supports sex allocation theory which predicts that in self-fertile plants resource allocation should be female biased whereas in outcrossing plants, allocation should be male biased. The lack of differences between the Christmas bell populations in other aspects of floral morphology, allocation pattterns and biology suggests that changes in ovule and pollen production precedes changes in other traits during the evolution of autonomous selfing. Overall, these findings suggest that tableland plants may have evolved self-fertility only recently and selection has had insufficient time to change floral traits. Alternatively, self-fertility may not have evolved recently and floral traits promoting outcrossing have been maintained by selection, imposed by inbreeding depression and/or overdominance.