Disentangling the causes of intrainflorescence variation in floral traits and fecundity in the hermaphrodite Silene acutifolia

Inflorescence architecture directly determines variations in floral traits and fecundity. Disentangling these patterns of variation is crucial to understanding intraplant variation, which sometimes is directly attributed to competition for resources with developing fruits. The dichasial cymes of Silene acutifolia were experimentally manipulated in the field to analyze whether the declines in petal size, ovule number, fruit set, and seed/ovule ratio along the inflorescence are constrained by ontogenetic development or are phenotypically plastic in response to environmental changes. At the same time, the level of pollen deficit was measured on different positions of the dichasia. The results showed clearly that all measured variables were more influenced by architecture than by resource competition with developing fruits; the removal of central (basal) and primary lateral flowers in the dichasia did not increase either the measures of floral characters or fecundity. On the other hand, although most of the decline in fecundity was due to architectural effects, there was also a pollen limitation, dependent to some degree on inflorescence position, which was probably due to lower pollen availability in the population when secondary flowers are in the female phase.