Manganese (Mn) is crucial as a trace element for plant metabolism, but high concentrations in soil can induce symptoms of toxicity. This study aimed to evaluate the metabolism of nitrogen compounds and biomass production in Canavalia ensiformis and Cajanus cajan, clarifying the effects of this metal on nitrogen metabolism. The soil was treated with Mn concentrations of 80, 100, 120, 140, and 160 mg kg⁻¹. Differential responses were observed in the metabolism of nitrogenous compounds between species. C. cajan affected nitrogen metabolism in shoots, roots, and nodules, with significant variations in amino acids, total soluble proteins, ureides, and root biomass concentration. In contrast, C. ensiformis showed stability in the concentrations of compounds, mainly ureides, and proteins, even with increasing doses of Mn in the soil. These findings highlight the importance of nitrogen metabolism in legumes studied as a key aspect for understanding their Mn tolerance mechanisms in soil.

The use of nickel (Ni) as a fertilizer remains a topic of debate, particularly in non-legume species, as Ni is required only in trace amounts for optimal plant function. Urea application in plants, whether foliar or root-based, relies on the urease enzyme to convert urea into NH_4⁺ and CO₂, with Ni serving as an essential cofactor. In this study, we conducted an experiment using a 2 × 2 factorial design, combining two urea concentrations [4% and 8% (w/v)] with the absence or presence of Ni (0.3 g L⁻¹ supplied as NiSO₄·6H₂O). Gas exchange parameters were measured two days after fertilization. We quantified urease enzyme activity, urea content, photosynthetic pigments, carbohydrates, and other nitrogenous metabolites. The presence of Ni during foliar urea fertilization significantly increased the photosynthetic rate and photosynthetic pigments, which we attributed to improved urea assimilation. The combination of urea and Ni enhanced urease activity, leading to higher levels of various nitrogenous metabolites. Ni positively influenced foliar urea assimilation, promoting its conversion into organic compounds, such as proteins, while mitigating the toxic effects associated with urea accumulation.

1. Trace elements (TEs) are described in the literature as trace metals, minor elements, or potentially toxic elements (Hossain et al. 2021). Some TEs, including boron (B), copper (Cu), iron (Fe), ...

The use of high biomass production plants in studies of metal phytoremediation is an established practice. This strategy aims to identify plants that tolerate unusual amounts of metals such as nickel (Ni). When comparing the biomass production capacity of a Ni hyperaccumulator, such as plants from the Alyssum genus, a production ranging from 0.5 to 4 t ha⁻¹ per crop cycle is observed ; on the other hand, species with a high biomass production capacity, for example Canavalia ensiformis, can produce 20 t ha⁻¹ to 25 t ha⁻¹ of green phytomass, 5 t ha⁻¹ to 8 t ha⁻¹ of dry phytomass and 1000 kg ha⁻¹ to 1800 kg ha⁻¹ of seeds. In this context, we planned an experiment to verify the tolerance and Ni accumulation capacity in Canavalia ensiformis. Our hypothesis was that increasing Ni concentration in the soil would not hinder the plant’s biomass production. We conducted a completely randomized experiment with five concentrations of Ni added to the soil and five replicates in a greenhouse during the vegetative stage. We evaluated the plant’s development, biomass production, and Ni accumulation in its organs. Our results demonstrated high tolerance to the metal, maintaining a biomass accumulation capacity of 68% of the dry mass in the soil with 277.8 mg kg⁻¹ of Ni at the highest concentration tested, compared to plants in the control soil. Considering that under these conditions the plants obtained a biomass of 10 g of leaves and 15 g of roots, and a nickel accumulation capacity of 75.05 mg kg⁻¹ in leaves and 102 mg kg⁻¹ in roots, the total Ni accumulation in the plants reached 2.37 mg Ni/plant in the soil with 277.8 mg kg⁻¹ of Ni. This soil Ni concentration would be lethal for most plants, and the metal concentration in the tissue exceeds the established limits for non-tolerant crops. With these results, this study aims to provide a foundation for improving the use of Canavalia ensiformis in phytoremediation.

The Neotropical freshwater stingrays of Potamotrygon genus present a unique and complex natural history and biogeographical pattern that can be traced to a marine origin and the colonization of the continental environment during the Miocene. During the evolution of potamotrygonids, several species of the parasitic fauna coevolved and co-opted concomitantly to their hosts during the colonization of the new environments. One striking example can be observed during the colonization of the upper Parana River region. However, few studies explored the ecological and taxonomic aspects of potamotrygonid parasites. In this work, we investigate aspects of the ecology and taxonomy of the species of Monogenea and Cestoda that are parasites the species of freshwater stingrays of the genus Potamotrygon in the upper Parana River. Our results indicate that at least six species of parasites are present in potamotrygonids in the region. Two of the observed parasites are putative new species and three of the parasitic species were identified for the first time in the region, hence expanding their geographic distributions. We quantified ecological aspects at different levels of communities for the collected parasite species. We compared the diversity in different locations and hosts and performed an exploratory analysis to investigate the differences in parasite abundance. Additionally, an identification key for the Monogenea and Cestoda species of the sampled region is provided.