The influence of sediment composition and irradiance on the growth and morphology of Myriophyllum spicatum L

Maximum summer biomass and morphology of Myriophyllum spicatum L. were influenced by both sediment composition and irradiance. Plants were grown in Lake Memphremagog, Quebec-Vermont along a natural depth gradient (1.5, 2 and 3 m) in buckets containing 100% fertile marsh sediment, 10% marsh sediment: 90% sand, or 100% sand. Shoot biomass responded to changes in sediment composition regardless of water depth. However, irradiance responses occurred only in the 100% marsh sediments. While sediment composition, irradiance and their interaction explained 91% of the total experimental variation, approximately 75% of the shoot biomass variation was attributable to sediment composition alone. Depth and the interaction term were each responsible for only 8%. These results appear consistent with both the morphology and natural distribution of M. spicatum .