Biomass Allocation in Fireweed Epilobium angustifolium L. (Onagraceae) in Response to Simulated Defoliation

Potted fireweed plants, Epilobium angustifolium L., were grown both from seed and root segments and subjected to early, late, and continuous defoliation and to apical excision during a single growing season. Seed-grown plants and root regenerates compensated completely for the early defoliation treatment and did not differ significantly from controls with respect to the dry weight of any yield component. Late defoliation significantly reduced the weight of flowers and fruit in seed-grown plants and root regenerates, and the annual increment of root weight in root regenerates. Continuous defoliation (early + late) significantly reduced the weight of flowers in seed-grown plants and the weight of both flowers and fruit in root regenerates. Apical excision significantly increased the total weight, shoot weight, and root weight of seed-grown plants but did not significantly affect any yield component in root regenerates. Reproductive allocation, defined as the percentage of total biomass in flowers and fruit, was significantly reduced in both seed-grown plants and root regenerates by the late and continuous defoliation treatments.