Effects of fragment size and water depth on performance of stem fragments of the invasive, amphibious, clonal plant Ipomoea aquatica

Many aquatic, clonal plants spread by vegetative fragments consisting of one to several ramets. Fragment size and physiological integration between ramets are likely to affect the establishment and growth of these fragments, and water depth is likely to affect the success of fragments in aquatic species that root in the sediment, but these effects have been little studied. To test the hypotheses that larger fragments perform better, that fragments perform better in shallower water, and that integration produces differences in the growth of ramets within fragments, we grew stem fragments of the cultivated, invasive, amphibious, floating, rooting plant Ipomaea aquatica with 1, 2, 3, or 4 nodes, which function as ramets, in water depths of 5, 20, or 40 cm for 8 weeks in the greenhouse. Final mean mass and leaf area per node were greater in larger fragments (e.g., 0.46 g and 49.3 cm2 in 4-node versus 0.16 g and 18.5 cm2 in 2-node fragments). Fragments accumulated about 3 times more mean biomass and leaf area in 5 cm (1.78 g and 196.7 cm2) than in 20 cm (0. 49 g and 49.9 cm2) or 40 cm (0.36 g and 34.9 cm2) deep water. Within larger fragments, most of the mean final mass was contained in the youngest ramet (66% in 3-node and 67% in 4-node fragments). Results supported all three hypotheses, and suggest that only stem fragments with 2 or more nodes are likely to promote vegetative reproduction in I. aquatica, and that physiological integration may concentrate growth in younger ramets.

► We studied how fragment size and water depth affect performance of clonal fragments.
► Individual ramets grew more within larger fragments.
► Water depth affected growth of floating clonal fragment.
► Physiological integration between ramets affected growth of fragments.