Initial decomposition of floating leaf blades of Nymphoides peltata (S.G. Gmel.) O. Kuntze (Menyanthaceae): causes, impact and succession.

ABSTRACT

Background: During a study on the outdoor floating leaf blade production of Nymphoides peltata (S.G. Gmel.) O. Kuntze (Fringed Water Lily), initial leaf blade decomposition was studied by simultaneously measuring infected, damaged and lost area of floating leaf blades. Methods: Data on initial decomposition over time were collected for all leaves during one growth season in four plots two in outdoor mesocosms and two in an oxbow lake. Each leaf was tagged uniquely upon appearance in a plot. The vegetation in the mesocosms differed with respect to plant species, one contained a monoculture of N. peltata and the other N. peltata associated with Glyceria fluitans (L.) R. Br. and G. maxima (Hartm.) Holmb. The lake plots were situated within a monospecific N. peltata stand, differing in depth and position within the stand. Leaf length, visually estimated percentages of damaged area for each damage type, and decay of the tagged leaves were recorded bi-weekly. When the leaf blades sunk under the water surface or disappeared completely, they were no longer followed. Under water the leaves decayed and were consumed by snails completely, so contributing to the detritus food chain. Results: The observed causes of damage on floating leaves were consumption and/or damage by waterbirds (Fulica atra), pond snails, caterpillars (Elophila nymphaeata, Cataclysta lemnata), chironomid larvae (Cricotopus trifasciatus), infection by a phytopathogenic fungus (Septoria villarsiae), senescence by autolysis, and microbial decay. Successional changes in causes of leaf decomposition and impacts of different causes are discussed.