Effects of reduced source-sink ratio on the cost of reproduction in females of Silene latifolia

Allocation to current reproduction is expected to lead to trade- offs in allocation to other life- history roles. We attempted to experimentally decrease the source- sink ratio in females of the dioecious plant species Silene latifolia in order to evaluate the nature of these trade- offs. We applied two experimental treatments to females from seven full- sibling families: delayed pollination of flowers and shading of flowers and fruits. Delayed pollination extended the period of flower maintenance, whereas shading prevented photosynthesis by the calyces. Both treatments altered female phenotype, but the response differed between treatments. Delaying pollination increased abortion of reproductive structures, probably because late pollination allowed the initiation of more floral buds. Increased flower production resulted in higher biomass allocation to inflorescence stems and may have been responsible for lower allocation to leaves. Preventing calyx photosynthesis decreased average fruit mass and total fruit mass but increased biomass allocation to leaves. We conclude that females of S. latifolia are capable of partially compensating for a decreased source- sink ratio by balancing their reproductive output to current carbon availability, at least within one growing season.