Effects of fragment size and sediment heterogeneity on the colonization and growth of Myriophyllum spicatum

Fragment colonization plays an important role in regulating the growth, reproduction, and expansion of submerged macrophytes. However, the influence of the interaction of fragment length and sediment heterogeneity on fragment colonization and growth is far from clear. Here, we investigated the effect of fragment length and sediment heterogeneity on the colonization and growth of a typical submerged macrophyte, Myriophyllum spicatum L. In an outdoor experiment, we examined two fragment sizes (6cm and 12cm in length) and three sediment types (type I, 0–12cm sand and 12–24cm clay; type II, 0–24cm mixture of sand and clay at a 1:1v/v ratio; and type III, 0–12cm clay and 12–24cm sand) and evaluated seven morphological traits (relative growth rate, relative elongation rate, shoot diameter, branching number, longest root length, average root length, and shoot to root ratio) and two physiological traits (total nitrogen content and total phosphorus content). Neither fragment size nor sediment type had a significant effect on the relative growth rate of M. spicatum. However, increased fragment size caused a significant decrease in relative elongation rate but a significant increase in shoot diameter and branching number. Fragments of the same size showed a higher branching number when grown in type III sediment than the other two sediments; furthermore, these fragments had the longest root lengths and highest average root lengths. However, they showed lower shoot to root ratios when grown in type I sediment than in type II and III sediments. Total phosphorus contents of M. spicatum, but not total nitrogen contents, were significantly higher when grown in type III sediment than in other two sediments. These data indicated that fragment size and sediment heterogeneity had a limited influence on colonization of M. spicatum. This effect might be accounted for by a high acclimation ability to these factors, mainly through adjustment of biomass allocation patterns and root characteristics.