Clover nodule bacteria as bioindicators of soils contaminated with heavy metals

Abstract

The article presents the results of a study of vital activity of nodule bacteria of Trifolium praténse, Trifolium hibridum, Trifolium alexandrinum and Trifolium incarnatum as environmentally friendly bioindicators in soil toxicity assessment. The study focused on the number of nodules and their stain with leghemoglobin. The materials were taken from the plots artificially contaminated with heavy metals (lead (Pb), arsenic (As), mercury (Hg), fluorine (F), zinc (Zn) and cobalt (Co)). The results of the experiments showed that environmental distress occurs when the nitrogen-fixing nodules are stained pink or red in the range of 8-15%, which indicates that the lead content in the soil exceeds the threshold limit value (TLV) by 1.2-1.5 times. A significant decrease in nodule activity and weak or no stain were observed with an increase in mercury concentration by 1.1 times. It was found that the mass of rhizobium or the supply of organic nitrogen obtained by plants from fixation from the air is directly dependent on the grass density. At high concentrations of heavy metals in the soil, the nodule bacteria lose the amount of leghemoglobin, therefore the stain of bacteria is disrupted, so this indicator can be used as a bioindicator in soil toxicity assessment.

Bio-Mercury Remediation Suitability Index: A Novel Proposal That Compiles the PGPR Features of Bacterial Strains and Its Potential Use in Phytoremediation

“…In the case of Hg, several authors have demonstrated the existence of bacterial populations in the rhizosphere of various plants that have the capacity to tolerate and/or eliminate this heavy metal from the edaphic environment [ 38 ]. Other studies, such as those conducted by Nonnoi et al [ 39 ] and Bekuzarova et al [ 40 ], have isolated bacteria from root nodules of different plant species ( Medicago spp. and Trifolium spp.…”

Enhancing of nitrogen fixation by legumes

“…It is known that the rhizobium-legume symbiosis is a consequence of the evolutionary activity of leguminous plants and nodule bacteria, the result of conjugate natural selection in the process of its historical development. The high degree of heritability of symbiotic characters and the direct relationship between nitrogen-fixing ability and plant productivity testify in favor of the effectiveness of symbiotic selection [5,6,7].…”

“…Having knowledge in the field of increasing nitrogen fixation of legumes, scientists have proved that there are a number of biological products that can increase the leghemoglobin in nodules and their amount in accumulation of biological nitrogen on leached chernozems of the North Caucasus region [6].…”