Altitudinal variation in size effects on plant reproductive effort and somatic costs of reproduction

Effects of plant size and altitude on reproductive effort (RE) and somatic costs of reproduction were examined for Ranunculus acris L. and Trollius eu ropaeus L. (Ranunculaceae) in subarctic Swedish Lapland. We estimated inves tment and cost during one reproductive season In terms of biomass (indexed B), nitrogen (N), and phosphorus (P). Above the tree line, plants of both s pecies had smaller size, and thus, smaller resource pools than at lower alt itudes. For Ranunculus, reproductive effort did not depend on plant size. I n terms of biomass, RE increased, while REN decreased, with altitude. For T rollius at lower altitudes, REB and REP varied inversely with size and alti tude. However, above the tree line, REB and REP showed no relationship with size. In terms of nitrogen, RE decreased with size for all populations. So matic costs of reproduction generally did dot vary with plant size and/or a ltitude in a similar manner as RE. Only in terms of P for Ranunculus, somat ic costs varied proportionally with reproductive effort. For plants of all sizes, somatic costs were often lower as compared to RE. Different effects of size and altitude on RE may result from varied environmental and morphol ogical constraints along the altitudinal gradient. However, patterns of var iation in RE were not reflected in the variation in somatic costs. We found an overall lack of conformity between reproductive effort and somatic cost s of reproduction.