The growth and nutrient balance of legumes can be disrupted in soils with increased nickel (Ni) concentrations. The inoculation of legumes with rhizobia, symbiotic nitrogen-fixing bacteria, can be used for the alleviation of trace metal stress in plants. This study evaluated the Ni tolerance of alfalfa rhizobia isolates and some plant growth-promoting traits in the presence of Ni: indole-3-acetic acid (IAA) production, Ni biosorption potential, and the effect of rhizobia on alfalfa (Medicago sativa L.) growth. The strains were characterized as Shinorhizobium meliloti, Sinorhizobium medicae, and Rhizobium tibeticum. In total, 70% of the tested strains tolerate up to 0.8 mM Ni, while 15% of the strains tolerate 1.2 mM Ni. The production of IAA was maintained in the presence of Ni until bacterial growth was stopped by raising the Ni concentration. Alfalfa seed germination is significantly reduced in the presence of 0.5 mM Ni, while a significant reduction in 10-day-old seedling length already occurs at a Ni concentration of 0.03 mM. In the plant experiment, when alfalfa was inoculated with rhizobial strains, nodulation was maintained up to 0.05 mM Ni, but a significant reduction in nodule number was detected at 0.01 mM Ni. At the concentration of 0.005 mM Ni, inoculation with 12 particular rhizobial strains significantly improved the number of nodules per plant, plant height, and root length, as well as plant shoot dry weight, compared to non-inoculated plants with Ni addition. However, higher concentrations caused a reduction in all of these plant growth parameters compared to the plants without Ni. The selected rhizobia strains showed a Ni biosorption capacity of 20% in the in vitro assay. The inoculation of alfalfa with effective rhizobial strains improves growth parameters compared to non-inoculated plants in the presence of certain concentrations of Ni.

The use of bioenergy crops such as Miscanthus x giganteus in phytoremediation could have both environmental and economic benefits, such as biomass production and soil conservation for crops. In our previous work, we showed that rhizobacteria from the rhizosphere of M. x giganteus stimulated metal extraction and uptake and enhanced the phytoremediation ability of treated M. x giganteus. In the present study, we conducted transcriptome analysis and qPCR to elucidate the molecular mechanisms underlying these interactions in response to bacterial treatment by identifying the candidate genes involved in growth and development processes and metal uptake. Using high-throughput RNA sequencing of root samples, we found that 5134 and 4758 genes were up- and downregulated in plants treated with the rhizobacteria consortium. Gene ontology analysis showed that the upregulated DEGs were significantly enriched in 32 terms, while the downregulated genes were significantly enriched in 63 terms. Our results confirmed the increased expression of two genes: the multidrug and toxic compound extrusion, also known as multi-antimicrobial extrusion (MATE) 40, known for its role in plant response to biotic and abiotic stress, and COBRA-like protein 1 belonging to the COBRA-like (COBL) gene family, which encodes a putative glycosylphosphatidylinositol (GPI)-anchored protein involved in cell wall thickening, cell elongation, and biomass increase when compared to untreated plants. We present the first insight into a mechanism whereby the interaction between the rhizobacterial consortium and M. x giganteus fosters plant growth and enhances its capacity for phytoremediation.

The pollution of soil by potentially toxic trace elements (PTE) is increasing every year and has become a serious problem worldwide. Plant growth is influenced by numerous interactions with the environmental factors and organisms from the surrounding soil, including high concentration of PTE. The aim of this research was to evaluate the possibility of growing orchardgrass in soils with an increased Ni concentration and improvement of the plant quality in these stressful conditions using Bacillus inoculums. In addition, the plant growth promoting traits and the germination of inoculated Dactylis glomerata seeds with Bacillus inoculants was examined. The main goal was to examine the effects of inoculums on plant yield, nutrient composition, and trace elements concentration in orchardgrass biomass. The ability of bacterial isolates to tolerate high concentration of Ni as well as the potential of these bacteria to enhance the germination of orchardgrass seeds was tested in vitro on Petri dishes. A pot experiment was conducted in soil with elevated Ni concentration, and plant dry mass, as well as the content of micro and macro elements in plant material was determined. The results of the pot experiment showed the positive effect of bacterial inoculation on shoot dry weight of orchardgrass, while the nitrogen content in orchardgrass shoots was slightly increased under the influence of bacterial inoculation. Furthermore, the content of microelements in plant material was reduced in inoculated plants.

Red clover (Trifolium pratense L.) is widely cultivated as forage crop. Due to the ability to accumulate potentially toxic elements from the soil, red clov

Introduction: The rhizosphere is a very active region containing a large number of microorganisms involved in complex biological and ecological processes. The microorganisms can improve the soil conditions, promote plant growth, and alleviate stress in plants under heavy metal contamination. Rhizobial bacterium ( Ensifer meliloti ) forms endosymbiosis with alfalfa ( Medicago sativa L.), providing nitrogen to the plant, and can mitigate the effects of different stress factors. Methods: This study aimed to evaluate the effects of rhizobial inoculation on alfalfa growth and rhizosphere microbiological properties in soils with increased nickel (Ni) concentrations during 2 years and across seasons. Two locations with different heavy metal concentrations, lower and higher, mainly Ni concentrations, but also lead (Pb) and chromium (Cr); six different rhizobial inoculants; and three different sampling time points were tested. The abundance of different groups of culturable bacteria (total number of microorganisms, fungi, actinomycetes, oligonitrophiles, Azotobacter , and ammonifiers), as well as microbial activity, that is, basal soil respiration rates, was evaluated in the rhizosphere soil of each treatment, location, and season. Results and discussion: The inoculation in some treatments significantly increased alfalfa yield in particular cuts, depending on the location ( p < 0.05) and treatment ( p < 0.05), with up to 38% increase compared to the control non-inoculated plants. Inoculations also influenced the abundance of specific microbial groups and soil respiration rates. Multivariate analysis of variance revealed a significant interaction between the tested factors [rhizobial inoculation ( p < 0.05), heavy metal concentrations ( p < 0.05), and seasons ( p < 0.05)] on all evaluated soil microbiological properties. Generally, the total number of microorganisms was positively influenced by inoculation and varied among different rhizobial treatments within the same field and season. The increased number of rhizosphere bacteria was positively correlated with yield in some cuts. Conclusion: The results show the potential of inoculation with particular rhizobia in the improvement of alfalfa yield in Ni-contaminated soils and overall microbiological properties and indicate the complexity of the interactions of multiple factors in the environment.

Acid soils are often a limiting factor in the production of most cultivated plants. In practice, the application of inadequate, physiologically acidic fertilizers, urea and NPK, is often encountered, which further worsens the already poor physicochemical properties of such soils. In this study, the influence of different amounts of NPK and urea fertilizers and methods of their application on the chemical properties of a very acidic soil and the accumulation of essential biogenic elements (N, P, K, Ca, Mg, and Al) in raspberry plants (leaves and fruits) was evaluated. The field trial with the raspberry plants was set up on a very acidic soil (pH in KCl 3.6), type Dystric Cambisol, and was monitored for 2 years. The application of NPK and urea mainly increased soil acidity in the second year in all treatments (for 0.10–0.18 pH unit) (except for urea applied in rows). The application of higher amounts of NPK increased the content of available forms of P (for 9.3–30.8 mg/kg) and K (for 57–95 mg/kg) in soil in both years, as well as exchangeable Ca (for 200–510 mg/kg) and Mg in the first year (15–165 mg/kg). The introduction of fertilizers in rows, compared to fertilization of the entire surface, influenced the reduction in mobile Al (especially when applying NPK, from 5.89 to 7.13 mg/100 g), the increase in mineral N and K content in the soil, and the increase in Ca and Mg only when applying urea, i.e., P when applying NPK in rows. In the leaves, the application of fertilizers in rows increased the content of Ca and Mg in the first year and P and K in the second year. In the fruits, the content of all estimated elements was not in correlation with their content in leaves and the fertilizer application, which indicates the influence of other ecological and biological factors on plant nutrition.