Heating effect by perianth retention on developing achenes and implications for seed production in the alpine herb Ranunculus glacialis

Abstract

Petals of the alpine, arctic perennial herb Ranunculus glacialis are retained also during seed maturation, as opposed to most species where the petals wither after they have contributed to insect attraction during anthesis. To assess the adaptive significance of perianth retention after anthesis for annual reproduction, we experimentally removed perianths of R. glacialis and explored its impact on achene surface temperature, the growth rate of achenes, carbon allocation, and seed production. Perianth removal immediately after anthesis decreased achene surface temperature, decelerated the growth of achenes and reduced seed set, compared to plants with intact perianth. Measurement of mass allocation showed no further perianth growth during seed maturation, and a 13C labelling experiment demonstrated that photosynthate allocation to perianths during seed maturation was much smaller than developing achenes. Thus, annual seed production of R. glacialis might be accelerated by perianth retention during seed maturation, while the cost of perianth retention is small compared to that of seed development. In alpine and arctic environments, cold temperatures limit the growth rate of achenes. Hence, the heating of developing achenes by perianth retention might be an adaptive trait that enhances female reproductive success in this arctic, alpine species.