Relationships between non-structural carbohydrate concentration and flowering in a subtropical herb, Heliconia caribaea (Heliconiaceae)

Heliconia caribaea, an understory herb that occurs in the rain forests of Puerto Rico, produces large modular flower structures (racemes) which are composed of a series of sequentially produced bracts. We hypothesized that seasonal carbohydrate concentration patterns exist in H. caribaea, and that those patterns were related to development of reproductive structures. To test this hypothesis, we collected tissue samples from three whole excavated plants and from the leaf subtending racemes from replicates of five raceme sizes (4, 6, 8, 10, and 12 bracts per raceme) at three times during the flowering season. Plant tissue was analyzed for soluble sugars, starch, and total non-structural carbohydrates (TNC). For leaves subtending racemes, TNC and starch levels increased significantly at the end of the flowering season. This pattern did not vary among plants with different sizes of raceme. Whole plants displayed decreased concentration of soluble sugars in some plant structures (petiole, raceme and stem) during the flowering period, with starch levels largely invariant, indicating that reproduction was supported primarily by current photosynthesis. We have found evidence that there is seasonal variation in the pattern of carbohydrates in H. caribaea, which coincides with the flowering season, but is independent of raceme size.