Inoculation with Azospirillum brasilense has promisingly increased plant yield and nutrient acquisition. The study aimed to estimate the dose of A. brasilense that increases yield, gas exchange, nutrition, and foliar nitrate reduction. The research was carried out in a greenhouse at Ilha Solteira, in a hydroponic system in randomized blocks with four replicates. The treatments consisted of doses of inoculation with A. brasilense strains AbV5 and AbV6 via nutrient solution (0, 8, 16, 32, and 64 mL 100 L⁻¹). Inoculation with A. brasilense at calculated doses between 20 and 44 mL provided the highest fresh and dry mass of shoots and roots, number of leaves, and leaf yield. In addition, the calculated doses of inoculation with A. brasilense increased the accumulation of N, P, K, Ca, Mg, S, B, Fe, Mn, and Zn in shoots and roots, except the accumulation of Ca in roots. It also increased cell membrane integrity index (15%), relative water content (13%), net photosynthesis rate (85%), intracellular CO₂ concentration (15%), total chlorophyll (46%), stomatal conductance (56%), transpiration (15%), and water use efficiency (59%). Hence, inoculation with A. brasilense at doses between 20 and 44 mL 100 L⁻¹ is considered the best approach for increasing the growth, yield, accumulation of nutrients, and gas exchange of hydroponically grown iceberg lettuce.

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.

When present in excess in the environment, nickel (Ni) can bioaccumulate along the food chain, and become toxic to plants and animals. Phytoremediation represents a sustainable alternative, using plants for soil decontamination. This study aimed to evaluate the growth and phytoremediation potential of four Crotalaria species, cultivated in Ni-contaminated soil. The study was conducted in a greenhouse, under a randomized block design, and a 4 × 5 factorial scheme, containing four species (C. juncea, C. spectabilis, C. breviflora, and C. ochroleuca) and five Ni treatments (0, 35, 70, 140, and 280 mg kg⁻¹). When Ni concentration reached 70 mg kg⁻¹, shoot dry mass decreased by approximately 52% in C. juncea, 53% in C. ochroleuca, 81% in C. breviflora, and 46% in C. spectabilis, compared to the control. C. juncea, C. ochroleuca, and C. breviflora maintained satisfactory growth at 35 mg kg⁻¹ and, for C. breviflora, this concentration increased root dry mass. All species showed high Ni translocation to the shoot, indicating potential for phytoextraction. The concentrations observed did not reach the threshold commonly used to define hyperaccumulator plants (>1000 mg kg⁻¹ dry mass). However, in C. spectabilis, the highest Ni dose led to an increase in root translocation and reduced shoot translocation. Therefore, Crotalaria species demonstrate potential for Ni phytoremediation, although they differ in strategies regarding growth, accumulation, and Ni mobilization.