Nitrogen is a major plant macronutrient and its supply affects the entire metabolism of plants. This study evaluated the effect of different nitrogen concentrations in the nutrient solution: 0, 4.2, 8.4, and 12.6 mg L⁻¹ Mexican marigold (Tagetes erecta L.) var. Inca plants in an open soilless culture system under greenhouse conditions on the concentration of chlorophylls, carotenoids, phenolics, and flavonoids derived from the secondary metabolism, as well as on the antioxidant activity in different tissues. With the 12.6 mg N L⁻¹ dose, chlorophylls a, b, and total chlorophyll concentrations increased by 98.8, 11.9, and 56.6%, respectively. The highest concentrations of total carotenoids in flowers, 28–30%, were recorded in plants with doses of 8.4 mg N L⁻¹. With doses of 12.6 mg N L⁻¹, phenolic compounds and total flavonoids increased in leaves, but decreased in flowers. The low and medium N concentrations increased the antioxidant activity with respect to the control without N by 53% and 50.2%, respectively. We conclude that the applications of N in Tagetes erecta differentially affected the concentrations of photosynthetic pigments and biomolecules with antioxidant capacity, and that such effects were dependent on the doses of N tested and the plant organ evaluated.

Negative effects of salt stress may be counteracted by adequate management of sulfated nutrition. Herein, we applied 3.50, 4.25, and 5.00 mM SO₄²⁻ in a nutrient solution to counteract salt stress induced by 75 and 150 mM NaCl in cabbage cv. Royal. The increase in NaCl concentration from 75 to 150 mM reduced the contents of macronutrients and micronutrients in the shoot. When increasing from 3.50 to 4.25 mM SO₄²⁻, the contents of nitrogen (N), phosphorous (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S) in shoots were enhanced, at both concentrations of NaCl. Increasing from 3.50 to 4.25 mM SO₄²⁻ enhanced iron (Fe), zinc (Zn), manganese (Mn), and sodium (Na) concentrations with 75 mM NaCl. With 150 mM NaCl, the increase from 3.50 to 4.25 mM SO₄²⁻ enhanced the contents of Cu and Mn, but also those of Na. Chlorophylls a, b, and total decreased as the concentration of SO₄²⁻ increased in plants treated with 150 mM NaCl. With 75 mM NaCl, carotenoid concentration had a positive relationship with SO₄²⁻. Hence, the 4.25 mM SO₄²⁻ concentration increased the contents of macronutrients and micronutrients in the presence of 75 mM NaCl, while, with 150 mM NaCl, it improved the contents of macronutrients except K. The chlorophyll a/chlorophyll b ratio remained close to 3 when the plants were treated with 5.00 mM SO₄²⁻, regardless of NaCl. Similarly, this level of SO₄²⁻ increased the concentration of carotenoids, which translated into reductions in the total chlorophyll/carotenoid ratios, indicating a protective effect of the photosynthetic apparatus. It is concluded that higher doses of sulfur favor the accumulation of nutrients and increase the concentration of carotenoids under salt stress.

We evaluated the effects of neodymium (0.000, 2.885, 5.770 and 8.655 mg · L ⁻¹ ) and zinc (0.1, 0.2 and 0.3 mg · L ⁻¹ ), as well as their interaction on lettuce plants in hydroponics. Applications of 2.885 mg Nd · L ⁻¹ and 5.770 mg Nd · L ⁻¹ increased plant height, number of leaves and leaf area, as well as fresh and dry stem, root and total biomasses. Root volume was greater in plants treated with 2.885 mg Nd · L ⁻¹ . With 0.1 mg Zn · L ⁻¹ , plant height, leaf area and fresh stem, root and total biomass were greater, while applying 0.3 mg Zn · L ⁻¹ increased the ratio of dry biomass of stems and roots. Plants exposed to 5.770 mg Nd · L ⁻¹ + 0.3 mg Zn · L ⁻¹ exhibited greater leaf length. The ratios of fresh and dry biomass of stems and roots increased in plants treated with 8.655 mg · L ⁻¹ Nd + 0.3 mg Zn · L ⁻¹ . Dry biomass weights of stems, roots and total were the highest in plants treated with 20 mg Nd · L ⁻¹ + 0.1 mg Zn · L ⁻¹ . Nd significantly increased foliar concentration of N, P and K. Hence, Nd and Zn improve growth and nutrition.

The use of plant growth-promoting bacteria (PGPB) tolerant to abiotic stress factors can enhance plant performance when applied under both optimal and stress conditions in crops. In this study, bacterial strains associated with the rhizosphere of the halophyte Distichlis spicata were isolated and characterized for their ability to produce siderophores, solubilize phosphate, synthesize indole-3-acetic acid (IAA) and exopolysaccharides (EPS), and tolerate salinity. IAA production and antioxidant capacity were further assessed under saline stress. As expected, salinity negatively impacted bacterial growth, IAA biosynthesis, and antioxidant activity—even in strains from a salt-tolerant plant. Nevertheless, all strains except RD2 maintained growth and IAA production in LB broth supplemented with up to 1 M NaCl. Five halotolerant strains (RD2, RD4, RD17, RD26, and RD27) were selected for greenhouse inoculation assays in tomato (Solanum lycopersicum) seedlings. Inoculation with RD26 significantly enhanced seedling performance, promoting tomato growth, increasing leaf area by 22%, stem diameter by 17%, shoot dry biomass by 30%, and root biomass by 27% as compared to the uninoculated control. RD27 and RD4 also improved shoot biomass by 25 and 23%, respectively. Based on 16S rRNA gene sequencing, RD26 was identified as Pseudomonas sp. and RD27 as Zhihengliuella halotolerans. These findings demonstrate that salt stress impairs plant growth-promoting traits in rhizospheric bacteria, yet selected strains such as RD26 and RD27 can significantly promote plant growth. Their use as bioinoculants represents a promising strategy for improving crop performance in saline environments.

We tested the effect of varying percentages (v/v) of peatmoss and compost (60/40, T1; 40/60, T2; and 20/80, T3) on growth and macronutrient concentration of lulo (Solanum quitoense Lam.) seedlings in a completely randomized experiment with ten replicates under greenhouse conditions. Lulo seedlings displayed higher plant height and stem diameter when grown in T1 and T2, as compared to T3. In root tissues, N concentration was higher in plants grown in T1, and the same trend was observed in leaves, though differences were not significant in the latter. All other nutrient concentrations analyzed in root tissues were higher in plants under T3. These results are directly related to a higher biomass production in roots as compared to shoots (52.5% higher) found in T3. In leaf tissues, however, significant increases in plants exposed to T3 were only evident for Ca and S concentrations (i.e., 10.6 and 2.6 g kg⁻¹ DBW). Considering dry biomass weight (DBW), lulo plants exhibited a significant and positive correlation between shoot (ShDBW) and total dry biomass (TDBW), whereas low and negative correlations were observed between root DBW and ShDBW. Therefore, a peatmoss/compost ratio of 0.66 (40/60, T2) results in a better plant growth performance, ensuring a good plant nutrient status for lulo seedlings.

The effects of three fertilization methods (FM) using the Peters Professional® 30N-10P-10K water soluble fertilizer were analyzed: fertilization in irrigation water (FIW), foliar fertilization (FF), and their combination (FIW + FF), as well as two substrate particle sizes (SuPS): larger particle size (LPS) and smaller particle size (SPS), on the growth and macronutrient status of Laelia anceps subsp. anceps (Orchidaceae). A 3 × 2 factorial experiment was established. Aerial and root growth, dry weight and concentration of macronutrients N, P, K, Ca, and Mg in leaves, pseudobulbs, and roots were all evaluated. The interaction of the study factors resulted in a greater number of leaves, while by simple effects, greater leaf area, number of pseudobulbs, root volume, and dry matter of leaves and roots were obtained, when FIW and LPS were used. With FF, greater growth in root volume was observed. There were no differences in the concentration of N in the growth organs analyzed, but due to the interaction of factors, a higher concentration of P, K, Mg, and S was observed in roots, mainly with FIW + FF and SPS; although for P, there was a higher concentration in FIW and LPS. In the case of SPS, the concentrations of K and S were higher in leaves, and in pseudobulbs P, K, Ca, Mg, and S were higher. The results showed that there are positive effects on plant growth when FIW and LPS are used, while higher concentrations of nutrients in leaves, pseudobulbs and mainly in roots are observed when using SPS.