Mineral Nutrition of Plants After Application of Growth-Promoting Rhizosphere Bacteria into Copper-Contaminated Soil

The effect of introduction of plant growth-promoting rhizosphere bacteria from the genus Pseudomonas on the mineral nutrition of spring wheat plants grown on agricultural gray soil artificially contaminated with high concentrations of copper has been studied in pot experiments. The plants were grown up to the booting stage on the soil contaminated with copper nitrate at a dose of 300 mg Cu/kg of soil against the background of PK fertilizer application. The content of copper and biophilic elements (N, P, K, Ca, Mg, Fe, Mn, and Zn) in the vegetative mass and roots after combustion in a mixture of HNO3 : HClO4 (2 : 1) was determined using inductively coupled plasma optical emission spectrometry (ICP-OES). The content of potassium was determined by the flame photometry. The nitrogen content was determined by the phenol method after the burning of a plant material in diluted sulfuric acid in the presence of a catalyst. The introduction of bacteria increased plant resistance to elevated copper concentrations and promoted an increased plant biomass, thereby reducing the phytotoxicity of the heavy metal. The positive effect of the bacteria was attributed to improved mineral nutrition of the plants and enhanced uptake of biophilic elements from the contaminated soil. At the same time, bacteria generally did not affect the content of almost all elements in the vegetative mass of the plants and increased the uptake of elements due to the plant growth stimulation likely caused by the bacterial production of physiologically active compounds. The stimulation of the growth of plants contaminated with the heavy metal and the increase in its uptake when using bacteria occurred without changes in the soil reaction. An improvement in the plant mineral nutrition, along with the enhanced barrier capacity of the root system to increase the uptake of the heavy metal by roots when using bacterial treatments, serves as the primary mechanism for stimulating the growth of contaminated plants.