With the growth of the world population, cadmium (Cd) concentration in the environment has increased considerably as a result of human activities such as foundry, battery disposal, mining, application of fertilizers containing toxic elements as impurities, and disposal of metal-containing waste. Higher plants uptake N as ammonium (NH), nitrate (NO ), and many other water-soluble compounds such as urea and amino acids, and nourishing plants with N, providing part of it as NH, is an interesting alternative to the supply of this nutrient in the exclusive form of NO under Cd toxicity. The objective was to evaluate the influence of NO /NH proportions on the development and tolerance of tomato plants grown under the presence of Cd in the culture medium. The experiment was conducted in a completely randomized block design in a 3 × 3 factorial arrangement consisting of three Cd rates (0, 50, and 100 μmol L) and three NO/NH proportions (100/0, 70/30, and 50/50) in the nutrient solution. To this end, we quantified the responses of the antioxidant enzymatic system and productive and functional changes in Solanum lycopersicum var. esculentum (Calabash Rouge). Shoot biomass production decreased with the maximum Cd rate (100 μmol L) tested in the growth medium, whereas the NO /NH proportions and other Cd rates did not significantly influence this variable. The lowest SPAD values were observed at the 100/0 NO /NH proportion and in plants exposed to Cd. The largest accumulation of the metal occurred in the shoots at the NO /NH proportion of 70/30 and at 100 μmol L Cd and in the roots at 100/0 NO/NH and with 50 and 100 μmol L Cd. The concentration and accumulation of NO were highest at the NO/NH proportion of 100/0 in the shoots and at 50/50 NO/NH in the roots, whereas for NH, values were higher as the proportion of N supplied in the form of NH was increased. The nitrate reductase enzyme activity decreased with the Cd supply in the nutrient solution. The antioxidant system enzymes were activated as we increased the NO/NH proportion and/or Cd rates added to the nutrient solution in both shoots and roots of the tomato plant, except for ascorbate peroxidase. Based on the results obtained, if the plant is to be used as a food source as is the case of tomato, the 100/0 NO/NH proportion is the better alternative because it resulted in higher Cd accumulation in the root system over the translocation to the shoots and consequently to the fruit.
Nitrogen (N) can alleviate metal toxicity. However, as of yet, there have been no studies showing the efficacy of NO/NH in mitigating Cu toxicity. The objective of this study was to evaluate the Cu toxicity on the nutritional and productive attributes of Panicum maximum cv. Tanzania as well as the role of NO and NH ratios in nutritional homeostasis. The experiment was conducted using 3 × 4 factorial treatments arranged in a randomized complete block design with three replicates. The treatments were three NO/NH ratios (100/0, 70/30, and 50/50) and four Cu rates (0.3, 250, 500, and 1000 μmol L) in nutrient solution. Copper concentrations in the diagnostic leaves (DL) were highest in plants grown under 70/30 NO/NH ratios and a Cu rate of 1000 μmol L. In this combination, it was observed that DL had higher concentrations of NH, greater glutamine synthetase activity, lower chlorophyll concentration (SPAD value), and lower shoot dry mass, suggesting high disorders of nutritional homeostasis. Plants receiving N in the form of NO and 1000 Cu μmol L showed that DL had lower concentrations of Cu, higher concentration of chlorophyll, higher NO concentration, higher nitrate reductase activity, and higher NO accumulation in the roots, suggesting a reduction in disorders of nutritional homeostasis. The disorders on mineral uptake, N assimilation, and biomass production caused by Cu toxicity are shown to be affected by NO/NH ratios, and N supply via NO allowed for better homeostasis of the forage grass.
The interaction of natural reactive phosphate with poultry litter may increase the production of forage grasses as a result of phosphorus (P) uptake. This study's goal was to analyze growth, production and P concentration of diagnostic leaves of forage grasses fertilized by an Arad reactive phosphate + poultry litter association. The experiment employed a 2 3 factorial, with the following factors: forage grasses (Urochloa brizantha and Panicum maximum), Arad rates (0 and 50 mg dm-3 P 2 O 5), and poultry litter (0 and 7.5 g dm-3). At the first harvest, the highest dry-matter production of leaves, sheaths + stems and shoots occurred in the interaction P. maximum × Arad × poultry litter. P concentrations in diagnostic leaves as well as number of leaves were similar between forage grasses, but higher in the interaction between Arad + poultry litter when compared to isolated fertilizers. At the second harvest, dry-matter production of shoots and sheaths + stems was higher in the U. brizantha + poultry litter interaction than in other interactions. Compared to the other fertilizers, P concentration in the diagnostic leaves at second harvest was higher in grasses fertilized with poultry litter. At second harvest, the number of leaves and tillers was highest in the U. brizantha + Arad + poultry litter interaction, followed by the Arad + poultry litter interaction. The association of Arad and poultry litter promotes adequate P nutrition and biomass production of forage grasses, and can therefore be considered an important instrument for the establishment of these grasses.
Nitrogen (N) is the most important nutrient in crop productivity and silicon (Si) increases the uptake of nutrients and affect the uptake of N. The objective of this study was to evaluate the effect of Si combined with rates of N on the growth, root development, uptake of N and Si, assimilation of N, and photosynthesis of the tomato plants (Solanum lycopersicum). A factorial 3 × 3 was used, with rates of Si 0 (control treatment), 1, and 3 mmol L–1, and rates of N 5 (control treatment), 15, and 25 mmol L–1 in the nutrient solution. The rates of N did not affect the dry mass production and uptake of Si. However, the application of Si improved the plant growth and accumulation of Si and N. Relating to control treatment, the rate of Si 1 mmol L–1 increases the dry mass production and accumulation of Si and N in order of 52, 37, and 54 %, respectively. Although the rate of N did not increase the plant growth, it was verified that the N 15 mmol L–1 improves the concentration and accumulation of N in the shoots, and the relative concentration of chlorophyll with values of 43.5, 67, and 14 %, respectively, compared to the control. The supply of Si under low and high availability of N improved the glutamine synthetase, but at the rate of N 25 mmol L–1, a decrease in the transpiration rate and stomatal conductance was verified. Under the high availability of N, the glutamine synthetase raised 78 % as an effect of Si 3 mmol L–1 compared to control treatment (Si 0 mmol L–1). Nevertheless, the transpiration rate and stomatal conductance decreased 49 and 52 % under that condition. The excess of N 25 mmol L–1 negatively affected the root development, but under that condition, the application of Si increased the root length, root surface, and root hood in order of 70, 40, and 77 % compared to the control treatment. Application of Si is recommended for tomato growth, especially when cultivated with high N availability. The application of silicon enhances the plant growth, root development, nutrient uptake, nitrogen assimilation, and photosynthesis of the tomato plants cultivated under rates of N. We recommend the use of Si 3 mmol L–1 and N 15 mmol L–1 for the tomato plants under the nutrient solution
The nitrate (NO 3-) reduction process is complex and has a high energy cost for plants when N is provided exclusively as NO 3
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