Floating mat as a habitat of Cicuta virosa, a vulnerable hydrophyte

Abstract

To investigate the function of floating mats in seedling establishment and growth of Cicuta virosa, a vulnerable hydrophyte, we surveyed the seedling distribution in the field and examined the growth increment in mesocosms formed by planting C. virosa on both artificial plant mats and base soil. Seedling density and coverage on floating mats and their edges, with high levels of solar radiation and sufficient water level, were significantly higher than those on soil. In the mesocosm experiment, shoot and root dry weight in soil was twice that for artificial mats, and these significant differences reflected nitrogen availability in the substrates. However, there was no significant difference in the number of flowering stalks, tiller or stem width, despite the difference in the level of nutrients between the substrates. These results show that floating mats provide sufficient water level and light-mitigated competition with nutrient limitation under continuous disturbance. This was advantageous to the establishment of seedlings and to the population sustenance of C. virosa. Also, high reproduction allocation of C. virosa sustained coexistence with prolific macrophytes on floating mats even though the overall growth on floating mats was worse than that on soil. Use of such floating mats could be a method for conservation of vulnerable hydrophytes.