DIFFERENCES IN BIOMASS ALLOCATION TO REPRODUCTIVE AND VEGETATIVE STRUCTURES OF MALE AND FEMALE PLANTS OF A DIOECIOUS,PERENNIAL HERB,SILENE ALBA (MILLER) KRAUSE

The pattern of biomass allocation of males and females and the sex ratio and growth characteristics of plants from three seed-size classes in Silene alba were investigated in a greenhouse study. Seed size significantly affected adult plant size and flower production of both male and female plants, but there was no significant difference in the proportion of males and females emerging in three seed-size categories. Male and female plants differed in the proportion of total biomass allocated to vegetative and reproductive structures and these differences were consistent across all seed-size categories. Males allocated a greater proportion of their biomass to flowers than did females. Female reproductive effort was dependent upon the percentage of flowers producing mature capsules. Only females with greater than 20% fruit set have a higher reproductive expenditure than males. Consequently, female expenditure is potentially greater than males, but is spread out over a longer portion of the growing season. This difference in the timing of reproductive expenditures by males and females allows females to allocate more biomass to growth during the early flowering period and may therefore account for the common pattern in herbaceous perennial dioecious species in which adult females are larger than adult males.