Female resource allocation in response to pollen availability in plants from freshwater cared salt marsh populations of Amaranthus cannabinus

Females of dioecious species could respond to pollen-limitation by extendin g their flowering period, by maximizing stigmatic surface area, or by produ cing stamens. Our objective was to determine female response to pollen avai lability in Amaranthus cannabinus (L.) Sauer, a dioecious annual. Plants fr om two southern New Jersey tidal marsh populations (fresh, FW; salt, SM) we re grown under spring greenhouse conditions until initiation of Bower devel opment. Females of each population were then paired as to height and vigor, and one of each pair was placed in a closed greenhouse room without males. The other females, surrounded by males, were placed in a comparable greenh ouse room. One month later at harvest, seed-bearing plants were senescing, while pollen-deprived plants were green with clusters of turgid stigmas at the base of almost every petiole and branch as well as at the end of branch es. There were no changes in sex expression; those females without pollen p roduced only female flowers. There were no significant differences in total biomass between treatments but striking differences in resource (biomass) allocation. Pollen-deprived plants allocated 61% (FW) and 37% (SM) more bio mass to reproductive structures other than seeds. For plants from both popu lations, the pollen-deprived plants allocated at least 68% more to stems, a nd 37% (FW) and 57% (SM) more to leaves. Confirming the earlier senescence of the pollinated plants, leaf drop at the time of harvest was 24% (FW) and 33% (SM) greater. Overall, females of freshwater and salt marsh population s showed a similar pattern in their allocation responses to pollen availabi lity.