The productive and reproductive biology of flowering plants X. Reproductive energy allocation and propagule output of five congeners of the genus Setaria (Gramineae)

Abstract

The energy allocation patterns to reproductive structures (RA) and the propagule output (P_N) of five annual weedy or ruderal fox-tail species (Gramineae)-Setaria viridis (2x) (including var. pachystachys (2x)), S. X pycnocoma (2x), S. faberi (4x), S. glauca (4x, 8x), and S. pallide-fusca (8x)-were studied in relation to their biomass on the materials from ten different wild populations in Toyama and Fukui Prefectures, Japan. In addition, the relationship between the RA and P_N was also critically examined.For all five fox-tail species, proportional partitioning of dry matter into total reproductive structures (caryopses, bristles, inflorescence axis and other persistent floral organs at the fruiting stage) (RA) shows considerable overlaps, but more or less constant within each taxon and independent of the biomass. On the other hand, the number of propagules produced per plant (P_N) is remarkably dependent on the size of plants and thus a function of the biomass. This high efficiency of energy allocation to propagules is evidently determined by the breeding system (i.e., predominant inbreeding) of these weedy annual species. However, the relationship between the RA and P_N showed no conspicuous trend, and thus the reproductive output is also independent of RA. The reproductive strategy found in Setaria is perhaps typical in such weedy annuals which grow chiefly in frequently disturbed, unpredictable environments. Another notable discovery was that, in spite of differences in ploidy levels (from 2x to 8x), all five species showed a very similar reproductive strategy, although slight but clear decrease was noted in the RA in response to the increase in ploidy levels, ranging from 49.52% (in diploids) to 27.53% (in tetraploids and octoploids). Seed weight (per gram), on the contrary, clearly increases in response to the increase in ploidy levels, i.e., ranging from 7.09×10^-4 g (in diploids) to 41.87×10^-4g (in octoploids).