P. praelongus is a submerged aquatic plant (submerged hydrophyte) with a perennial rhizome (root stalk). It requires a permanent water column and it does not createfloating leaves. It is a CS strategist, which means that this species is competitively quite proficient and tolerates ecological stress.
P. praelongus occurs in lakes, river floodplains (river oxbows, pools), moderately flowing water, ponds, or reservoirs. It grows especially in unpolluted mesotrophic water on humic or sandy soils, clayish, muddy or peaty beds, in depths of 0.2–2.0 m. The depth in which the species grows depends on the water transparency. In northern countries, it grows in streams and lakes with high water transparency and mainly gravel bottom and thus it grows in depths up to several meters (4 m and more). In the CR, it grows in pools 20–70 cm deep, where it requires a moderate shadow to prevent overheating. In Russia and in Slovenia, the species occurs in overgrowing waters, slowly running waters, even in flooded alluvial, in the depth of 2–3 m.
Potamogeton praelongus is known from several plant communities classified in various phytosociological alliances (Batrachion fluitantis Neuhäusl 1959, Ranunculion fluitantis, Oberdorfer 1977, Potamion Miljan 1933). P. praelongus is always monodominant in these plant communities. According to new classification, the plant communities with P. praelongus belong to the association of Potametum praelongi Hild 1959 in the frame of Potamion Miljan 1933 alliance. A low number of species is a typical feature of this association.
Electrical conductivity and pH are the most important factors for its growth. Electric conductivity of 110–410µS·cm-1and pH values of 7.1–8.4 are considered optimal. In northern localities (Norway, Sweden),pH values rank between 7.0 and 9.4, in Czech localities between 7.1 and 8.2. In all Czech localities there are high values of electrical conductivity (165–342 µS.cm-1), which indicates slightly eutrophic or eutrophic environment. Eutrophication was one of the most important reasons of extinction of this species in most of the Czech localities. In Norwegian and Swedish localities, the values of electrical conductivity are significantly lower (commonly measured values were 59–120 µS.cm-1).
The species has a very efficient photosynthesis and is able to efficiently use HCO3- ions as a source of carbon for the photosynthesis, which gives it advantage when growing in hard water. Therefore, the total alkalinity higher than 1.2 mekv·l-1 is beneficial. In the CR, the total alkalinity values rankinto1.36–1.62 mekv.l-1 in the river Orlice floodplain, 1.64 mekv.l-1 in the Ploučnice river oxbow near Heřmaničky and 3.02–4.09 mekv.l-1 in pools in the PLA Kokořínsko. The total alkalinity (TA) of 1.4 mekv.l-1 is known from the lake near Hamburk. In the Czech localities, the values of calcium concentration are of 50–62 mg.l-1 in the Orlice river floodplain, 46–66 mg.l-1 in the oxbow of the river Ploučnice near Heřmaničky and 39–96 mg.l-1 in pools in the PLA Kokořínsko. In the lake near Hamburk the calcium concentration of 52 mg.l-1 was recorded. In an experimental culture in Býšť, encrustations of CaCO3 were found on young leaves if the calcium concentration was higher than 85 mg.l-1.
The growth period of P. praelongus in central Europe lasts from April to September. It begins when the water temperature stabilizes above 10 °C, which is usually at the turn of March and April or in the first half of April. Apart from overwintering stems, new stems grow from the rhizome. Their base is in turions (vegetative banana-shaped white-yellow buds) growing upright from the rhizome. These vegetative structures are important not only for overwintering, but also for overcoming unfavourable conditions. Turions can also survive in anaerobic environment for a short time. Under good conditions, some stems hibernate and then flower; new stems grow stronger and are freshly green, fragile and shiny. P. praelongus flowers from May to June. The flowers are arranged in green spikes which rise above the water surfacefor a short time. Then they fall into the water, where the achenes mature. Old stems die. Achenes are mature in July or August; spikes with matureachenes rot off and fall to the bottom. Senescence in our conditions begins at the end of September and in October. Some of the stems die and fall to the bottom. Rhizomes with overwinteringturions and sometimes a few young stems survive the cold season.
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