Biological nitrogen fixation by legume-rhizobacterial symbiosis in temperate grasslands is an important source of soil nitrogen. The aim of the present study was to characterize the dependence of different accessions of T. fragiferum, a rare crop wild relative legume species, from their native rhizobia as well as additional nitrogen fertilization in controlled conditions. Asymbiotically cultivated, mineral-fertilized T. fragiferum plants gradually showed signs of nitrogen deficiency, appearing as a decrease in leaf chlorophyll concentration, leaf senescence, and a decrease in growth rate. The addition of nitrogen, and the inoculation with native rhizobia, or both treatments significantly prevented the onset of these symptoms, leading to both increase in plant shoot biomass as well as an increase in tissue concentration of N. The actual degree of each type of response was genotype-specific. Accessions showed a relatively similar degree of dependence on nitrogen (70–95% increase in shoot dry mass) but the increase in shoot dry mass by inoculation with native rhizobia ranged from 27 to 85%. In general, there was no correlation between growth stimulation and an increase in tissue N concentration by the treatments. The addition of N or rhizobial inoculant affected mineral nutrition at the level of both macronutrient and micronutrient concentration in different plant parts. In conclusion, native rhizobial strains associated with geographically isolated accessions of T. fragiferum at the northern range of distribution of the species represent a valuable resource for further studies aimed at the identification of salinity-tolerant N₂-fixing bacteria for the needs of sustainable agriculture, as well as in a view of understanding ecosystem functioning at the level of plant-microorganism interactions.

The aim of the present study was to assess heavy metal tolerance and its accumulation potential in coastal nitrophilic species Rumex maritimus, and to study the possible effects of nitrogen fertilizer and salinity on the characteristics of metal-treated plants. Two experiments were performed in partially controlled greenhouse conditions: (1) gradual treatment with increasing concentrations of Cd, Pb, Cu, Mn, and Zn; and (2) acute treatment with Cd, Pb, and Cu on the background of different nitrogen fertilizer amendment rates (0.15 and 0.30 g L⁻¹ N) and salinity (50 and 100 mM). R. maritimus plants were extremely tolerant to treatment with all metals, with no negative effect on total leaf biomass both in the case of gradual or acute treatment. However, the number and biomass of dry leaves increased under high doses of heavy metals, and the effect was more pronounced in the case of acute treatment. All studied metals were excluded from the roots and young leaves, predominantly accumulating in the dry leaves, reaching 250 mg kg⁻¹ for Cd, 2000 mg kg⁻¹ for Pb, and 500 mg kg⁻¹ for Cu. In the second experiment, the presence of increased nitrogen in the substrate positively affected the growth of R. maritimus plants and their morphological response to heavy metals, but salinity affected metal accumulation. Photosynthesis-related parameters, leaf chlorophyll concentration, and the chlorophyll a fluorescence parameter Performance Index Total confirmed that heavy metals had no negative effect on the physiological state of photosynthetically active leaves. It is concluded that R. maritimus plants have exceptional potential for practical phytoremediation needs due to the high tolerance and accumulation potential for heavy metals.