Does the relative importance of resource competition and architectural effect in floral variation vary with stages of floral ontogeny?

Abstract

Abstract Variation in floral allocation within inflorescences has been attributed to resource competition and/or architectural effect. The two hypotheses were extensively studied and both hypotheses were partly supported by previous studies. However, the relative importance of resource competition and architectural effect may vary with stages of floral ontogeny in a species. To detect the effects of ontogenetic stages on floral variation, we manipulated the 6-flowered inflorescences of Adenophora jasionifolia (Campanulaceae) by early, late, and non-thinning flowers. Our results indicated that pollen and ovule production of the remaining flowers were not significantly different between early and late thinning manipulations, suggesting that floral sex allocation was determined far before flowering, in support of the architectural effect hypothesis. Under hand-pollination treatments, early thinning but not late thinning resulted in a significant increase in seed number and seed set of the remaining flowers. Therefore, the increase in seed production of the remaining flowers related to the floral ontogeny. The resource competition for floral allocation was significant under early thinning rather than late thinning manipulation. Our results suggest that studies on floral variation within inflorescences should take into account the stages of floral ontogeny.