Effect of pH, dissolved organic carbon and total phosphorus concentrations on selected life history traits of Luronium natans (L.) RAF.

A hypothesis has been put forward that low pH or high concentration of total phosphorus (TP) and dissolved organic carbon (DOC) in the lake water are the factors responsible for observed extinction of the population of Luronium natans (L.) Raf., protected macrophyte species from the group of isoetids. A study was performed on 525 generative individuals collected from 21 lakes in Pomeranian Lakeland (NW Poland) and a correlation between the biometric characteristics and environmental conditions in the lakes was tested. The following life history traits have been analysed: size of individuals, their fecundity and allocation of biomass. The greatest and most fecund individuals grow in the lake water of pH 6.1-7.0, poor in TP (10.1-20.0 [mi]g dm^-3) and DOC (3.5-6.0 mg C dm^-3). The allocation of biomass of the individuals growing in the optimum conditions is as follows 46-54% in the leaves, 22-31% in the roots and 20-27% in the rhizome. In the lakes with water of pH < 5.0 or of TP3 > 20.1 [mi]g dm^-3 and DOC > 6 mg C dm^3, a statistically significant decrease in the size of the individuals and unfavourable changes in the biomass allocation are found. The main environmental factor responsible for dying out local populations of Luronium natans is a decrease of pH below < 5.0.