Costs of reproduction in circumpolar Parnassia palustris L. in light of global warming

Life-history theories predict competition and compromises between different reproductive and somatic (e.g., growth) functions in plants. This study concerns the costs of reproduction in an alpine herb, Parnassia palustris L., in light of global warming. The field experiments involved manipulations of temperature regime using open top chambers, and manipulations of the current level of reproductive investment by supplemental hand-pollination (SP) and bud removal (BR). The study continued for 2 years and costs of reproduction were evaluated in the second year by comparing reproductive outputs and growth between treatment groups. Flower manipulations carried out the first year had no statistically significant effect on reproductive or somatic variables in the second year, which suggests that reproductive costs in P. palustris are limited. Increased temperature, however, had a positive effect on a range of reproductive traits such as seed number, seed mass per fruit, mass per seed, and ratios between reproductive outputs and growth, but had no statistically significant influence on growth. No statistically significant interaction effects between flower manipulation and warming were revealed, which implies that the effects of flower manipulation in the first year does not differ statistically significantly between the two temperature regimes in the next year. We conclude that the lack of reproductive costs found in P. palustris at Finse expresses that resources are not restricted under a level that will induce high costs of reproduction. Furthermore, higher temperatures do not affect the costs, and finally, it appears that the reproductive costs are fine-tune controlled, which implies optimizing rather than maximizing of reproductive and somatic outputs.