Temporal changes in macro- and trace element concentrations in the rhizosphere soil of two plant species

The aim of the research was to assess the impact of root exudates of two widely distributed plant species, monocot (couch grass) and dicot (dandelion) on the concentrations of 27 macro- and trace elements in the rhizosphere soil of the plants. A field trial was carried out to study short-term variations in the concentrations of the elements when the plants grew separately or in close proximity to each other in non-contaminated soil and in soil contaminated by RbCl. During daytime, total amount of C and N in the rhizosphere soil of both plant species was found to be constantly decreasing. Similar variations were also found for Mg, Al, V, Ga, and As. The concentrations of some other elements (Na, Se, La, and Ce) showed a maximum value in the middle of day. These variations might be due to changes in the soil temperature. Contamination of soil by RbCl negatively affected the concentrations of several elements in the rhizosphere soil of couch grass and dandelion. The impact was more marked when the plants grew far from each other. Soil contamination by RbCl led to a decrease in number of natural isolates in bulk soil. In the soils taken from roots, of the plants grown in the Rb-contaminated soil, number of the same isolates increased compared with that in bulk soil, but level of the increase was different in the rhizosphere soil of couch grass and dandelion. The variations depended on whether these plants grew close to each other or separately.