Influence of environmental conditions on the regenerative capacity and the survivability of Elodea nuttallii fragments

The presented study was conducted to determine which environmental factors and conditions can affect the regenerative capacity and survivability of Elodea nuttallii [o1] and therefore the efficiency of mechanical management methods like cutting and harvesting. The influence of water temperature, light intensity and nutrient concentration in the sediment on the survivability and regenerative capacity of the invasive species E. nuttallii was determined in three laboratory and one field experiments. E. nuttallii fragments with one to four nodes were stored in aquaria under constant temperature and/or light conditions. To examine the influence of water temperature, four aquaria were kept at a constant water temperature of either 15°C or 20°C. The influence of light intensity was studied by shading the aquaria with different types of mesh. The fragments were stored at constant light intensities of 215, 161, 86 and 31 µmol photons m^–2 s^–1. Fragments in aquaria filled with sediment with 20 µg P₂O₅-P g^–1 soil, 150 µg P₂O₅-P g^–1 soil or without sediment were studied to determine the influence of the sediment. The results of the laboratory experiments showed how the mechanical management methods are most efficient during periods with low water temperatures, high turbidity or low global irradiation and nutrient poor waters. The field experiment was designed to study the influence of the nutrient compositions in the sediment on the growth and regenerative capacity of rooted E. nuttallii. E. nuttallii fragments were planted in compartments treated with PO₄^3-- and/or NH₄⁺-fertiliser and were trimmed after six weeks. The experiment revealed that the growth before a harvest and the growth after a harvest (regenerative capacity) differ significantly, depending on the nutrient composition in the substrate. An increase of the PO₄^3- concentration in the sediment, for example, reduced the growth of E. nuttallii before the harvest, but increased the growth after the harvest. A treatment with PO₄^3-- and NH₄⁺-fertiliser had an opposite effect on growth and regenerative capacity. The study proved that the environmental conditions have a significant influence on the efficiency of mechanical management methods.