Reproductive allocation and costs of reproduction in subarctic herbs : A resource-based perspective

Abstract: The influence of internal and external factors on two major plant life history components, i.e., reproductive allocation and costs of reproduction, was examined for nine perennial herbs in subarctic Swedish Lapland. In one study, comparisons were made between Sweden and the French Alps. Reproductive investment and costs were estimated in terms of biomass, nitrogen (N), and phosphorus (P). At high altitudes, reproductive effort (RE) was commonly lower and sexual shoots less frequently produced than at lower altitudes. However, effects of altitude were in some cases absent. This could be due to internal factors, such as meristem formation as in Ranunculus acris and low plasticity of reproductive structures as in Trollius europaeus.Reproductive investments varied between sexes in first-year Silene dioica plants. Female flowers produced more nectar than male flowers. At peak flowering, however, male plants offered 3.5 times mom nectar, due to their higher flower numbers. Pollen dry mass and N content per flower varied over the season, while the pollen P content remained constant. Sexual differences in allocation patterns depended on the resource used for comparison and whether absolute or proportional resource pools were assessed. Females and males had similar RE in terms of biomass and N, while males invested proportionally more P in reproduction. High allocation to flowers in males resulted in lower N content of over wintering parts compared to females.Reproductive investment was carried out at the expense of the somatic resource pool. However, the occurrence of a direct trade-off between reproductive and somatic functions depended on the focused resource. The traits expressing the trade-off between current and future reproduction varied between habitats for R. acris. Five out of nine examined traits expressed reproductive costs. Effects of experimental treatments may be hampered due to internal factors, e.g. meristem formation. It is important to select several resources, traits, and environments in future assessments of reproductive investments and costs of reproduction in plants.