Contrasting resource allocation patterns in Sedum lanceolatum Torr.: Biomass versus energy estimates.

Biomass determinations and microbomb calorimetry were used to assess resource allocation in Sedum lanceolatum Torr. between 2,257 and 3,726 m above sea level in the Front Range of the Rocky Mountains, Colorado, USA. In general, energy values did not differ within a tissue among sites, but did differ among tissue types. Flowers and leaves had the greatest energy content per gram ashfree dry weight. Total kilojoules per plant were homogeneous along the elevational gradient.Allocation patterns based on kilojoules of energy and grams of biomass were not highly correlated, with the exception of the percent investment in sexual tissues. Allocations to sexual tissues based on dry weight and energy were negatively correlated, revealing opposing trends of sexual investment with the increase in elevation. Due to the greater biomass investment in high energy leaves and flowers by populations of Sedum lanceolatum at higher elevations, allocation to sexual reproduction based on calorimetric analysis increased from 18.3 to 38.3% along the 1,469 m change in elevation. Although biomass can represent energy allocation in some taxa, for those species that change morphologically or physiologically along an environmental gradient, these two methods may not reveal similar trends.