Effect of environmental conditions on the populations of Luronium natans [L.] Raf.

The structure (aggregations` distribution, density, age structure) of Luronium natans L. (Raf.) populations has been studied in 21 lakes in the Pomeranian Lakeland (NW Poland), where the highest population density of this species is found in slightly acid (pH 6–7) waters, poor in DOC (<6.0 mg C dm⁻³) and phosphorus (<30.0 µg TP dm⁻³). Luronium natans reproduces mainly vegetatively and prefers shallow (1–2 m), mineral-organic (5.1–10.0% C) substrates. Seedlings represent about 10% of a population. High levels of pH (pH>8.0), concentration of carbon (>6.0 mg C dm⁻³) and phosphorus (>30.0 µg TP dm⁻³) impede the population growth. Under such conditions population density may be lower by as much as 80–90%, aggregation size smaller, and the proportion of generative stems higher. Luronium natans aggregation size depends on the depth: the deeper the location – the larger and denser the aggregation, the shallower the location – the larger the fraction of generative individuals (up to 98% of the population).