Threshold concentrations of cations in the external environment required for maintenance of the ionic balance between the organism of the invader Elodea canadensis Michaux and fresh water

Abstract

The content of sodium, potassium, calcium, and magnesium in the invader pondweed Elodea canadensis in field conditions is 14.5 ± 0.7, 56.2 ± 0.9, 241.5 ± 15.2, and 26.4 ± 0.2 mmol/kg wet mass, respec� tively; the content of various fractions of water is as follows: general 80.3 ± 0.7%, free 77.5 ± 0.8%, connected 2.73 ± 0.14%. The threshold concentrations of sodium, potassium, calcium, and magnesium in the water necessary to maintain the ionic balance between the plant organism and the medium are 0.0014-0.0021, 0.00013-0.00024, 0.12-0.16, and 0.0056-0.0075 mmol/L, respectively. Reduction of water mineralization is accompanied by a significant drop in the levels of sodium, calcium, and magnesium in plants, as well as by augmentation of concentration gradients of cations between the organism and the medium, thereby enhanc� ing the load on systems for maintenance of the water-salt exchange. Along with that, the amount of dry sub� stance in plants decreases, while that of water increases. Under such intense conditions, the power expenses to maintain the vital activity of the organism dominate the processes of accumulation of organic substances. On the basis of data on threshold cation concentrations in the medium, a comparative analysis for the ability of various species of aquatic organisms to master lowmineralized freshwater reservoirs is presented.