Heterophylly in the yellow waterlily, Nuphar variegata (Nymphaeaceae): effects of [CO2], natural sediment type, and water depth

We transplanted Nuphar variegata with submersed leaves only into natural lake sediments in pH-, CO(2)]-, depth-, and temperature-controlled greenhouse tanks to test the hypotheses that more fertile sediment, lower free CO(2)], and shallower depth would all stimulate the development of floating leaves. Sediment higher in porewater NH(4)(+)] favored floating leaf development. Low CO(2)-grown plants initiated floating leaf development significantly earlier than high CO(2)-grown plants, which produced significantly more submersed leaves and fewer floating leaves. Mean floating leaf biomass was significantly greater than mean submersed leaf biomass but was not influenced by CO(2) enrichment, whereas mean submersed leaf biomass increased 88% at high CO(2)]. At the shallower depth (35 cm), floating leaves required 50% less biomass investment per leaf than at 70 cm, and a significantly greater proportion of plants had floating leaves (70 vs. 23-43% at 35 vs. 70 cm, respectively) for the last three of the eight leaf censuses. Sediment type, water depth, and especially free CO(2)] all can influence leaf morphogenesis in Nuphar variegata, and the development of more and larger submersed leaves with CO(2) enrichment favors the exploitation of high CO(2)] when it is present in the water column.