Effects of nutrients and light in aquatic habitat on the growth of Hydrocotyle vulgaris when expanded from terrestrial to aquatic habitat

Many amphibious clonal plants in aquatic-terrestrial ecotones commonly expand from terrestrial to aquatic habitats. Nutrient availability and light intensity are both key factors affecting plant growth in aquatic habitats, but little is known about the role of nutrient availability and light intensity in aquatic habitats during the expansion of amphibious clonal plants from terrestrial to aquatic habitats, when clonal integration is maintained. We conducted a greenhouse experiment to simulate expansion from terrestrial to aquatic habitats of the amphibious clonal plant Hydrocotyle vulgaris. We grew basal portions of clonal fragments in soil and connected the apical portions of the same fragments to water which subjected to three levels of nutrient availability under a low or a high light condition. High nutrient level and light condition increased the growth of the apical portions of H. vulgaris and thus increased the performance of the whole clones. Meanwhile, root-shoot mass ratio of the apical portions and the basal portions were higher at the high light condition and the low nutrient level. Results suggest that the relatively high levels of nutrients and light condition in aquatic habitats can improve the expansion of apical portions from terrestrial to aquatic habitats. Our results also suggest that maintaining clonal integration may benefit the expansion of H. vulgaris via the trade-off of biomass allocation which can optimize the utilization of resources. These results may provide theoretical basis for community dynamics prediction and vegetation restoration in the ecotones such as wetlands.