Abstract：In this paper, the effect of plant density, sediment type, and macrophyte fragment size on the fragment colonization ability of Myriophyllum spicatum was evaluated in an outdoor experiment. The relative growth rate (RGR) was higher in the mud and low-density treatments than in the sand and high-density treatments. The relative elongation rate (RER) decreased with increasing density and fragment size, with RER values being much higher in the mud than the sand treatments. Both branching number and shoot diameter increased with decreasing density and increasing fragment size, and were significantly higher in the mud than the sand treatments. The shoot : root ratio was higher in the mud treatments than in the sand treatments. Total N content in both the shoot and root was significantly higher in the mud and low-density treatments than in the sand and highdensity treatments. Shoot P content only decreased with increasing density, while root P content was higher in the mud and low-density treatments than in the sand and high-density treatments. These data indicate that fragment colonization by M. spicatum is improved by large fragments, low density, and nutrient-rich sediments, and that these conditions contribute to the rapid population expansion of this species.
