Biomass production and uptake of sulfur, chromium and micronutrients by Tanzania guinea grass grown with sulfur and chromium.

Soil contamination caused by improper waste disposal can affect plant growth. Tropical forage plants have rapid growth, high biomass production and vigorous regrowth. Chromium (Cr) is one of the most common contaminants in the environment. Sulfur (S) is a nutrient involved in various cell detoxification processes. The objective was to assess the effects of excess Cr on biomass production and concentrations of this metal, S and cationic micronutrients, under conditions of varying supply of S for Tanzania guinea grass. The experiment was conducted in randomized complete blocks in a 3 × 4 factorial scheme, corresponding to three levels of S (0.1, 1.9 and 3.7 mmol L-1) and four levels of Cr (0.0, 0.5, 1.0 and 2.0 mmol L-1) in three replicates. Root surface area, shoot and root biomass production, concentrations of total S, sulfate-S, Cr and cationic micronutrients, and Cr transport factor were determined. S level of 1.9 mmol L-1 reduced the toxicity by Cr in Tanzania guinea grass, expressed by the higher shoot and root dry weight production, greater stability in the cellular concentration of sulfate-S and higher concentrations of micronutrients. It was concluded that the high availability of S reduced the toxicity by Cr(VI) in Tanzania guinea grass, expressed by the higher shoot and root dry weight production, greater stability in the cellular concentration of sulfate-S and higher concentration of micronutrients in the grass shoots.

Sulfur supply reduces barium toxicity in Tanzania guinea grass (Panicum maximum) by inducing antioxidant enzymes and proline metabolism.

Sulfur (S) can play essential roles in protecting plants against abiotic stress, including heavy metal toxicity. However, the effect of this nutrient on plants exposed to barium (Ba) is still unknown. This study was designed to evaluate the S supply on oxidative stress and the antioxidant system of Tanzania guinea grass under exposure to Ba, grown in a nutrient solution under greenhouse conditions. It was studied the influence of S/Ba combinations in nutrient solution on oxidative stress indicators (hydrogen peroxide, malondialdehyde, and proline) and antioxidant enzyme activities (superoxide dismutase, catalase, ascorbate peroxidase, guaiacol peroxidase, and glutathione reductase). The treatments consisted in thirteen S/Ba combinations in the nutrient solution (0.1/0.0; 0.1/5.0; 0.1/20.0; 1.0/2.5; 1.0/10.0; 1.9/0.0 - control; 1.9/5.0; 1.9/20.0; 2.8/2.5; 2.8/10.0; 3.7/0.0; 3.7/5.0 and 3.7/20.0 mM of S and Ba, respectively). The plants were grown for two growth periods, which consisted of fourteen days of S supply and the eight days of Ba exposure each one. The severe S deficiency decreased the superoxide dismutase activity, regardless of Ba exposure in recently expanded leaves and culms plus sheaths. However, supplemental S supply (above 1.9 mM S, which corresponds to S supply adequate to plant growth) it improved the superoxide dismutase activity in these tissues under high Ba concentrations. Conversely, the severe S deficiency increased the activities of catalase, ascorbate peroxidase, and glutathione reductase in grass leaves slightly, without Ba exposure influence. It was observed that the supplemental S supply also induced the guaiacol peroxidase activity and proline production in culms plus sheaths under high Ba rates, showing values until 2.5 and 3.1 folds higher than the control treatment, respectively. In plants under exposure to 20.0 mM Ba, the supplemental S supply decreased the malondialdehyde content in culms plus sheaths in 17% compared to 1.9 mM S. These results indicate that supplemental S supply can mitigate Ba toxicity in Tanzania guinea grass, mainly by improving superoxide dismutase and guaiacol peroxidase activities, and proline metabolism.

Partial replacement of nitrate by ammonium increases photosynthesis and reduces oxidative stress in tanzania guinea grass exposed to cadmium.

In order to grow and effectively uptake and accumulate cadmium (Cd), plants used for phytoextraction have to cope with toxicity, which may be influenced by the supply of nitrate (NO3-) and ammonium (NH4+). Thus, we evaluated the effect of these nitrogen forms on the photosynthetic and antioxidant enzyme activities of Panicum maximum cv. Tanzania (tanzania guinea grass) under Cd stress. Plants were grown in nutrient solution under greenhouse conditions and subjected to a 3 × 3 factorial experiment. They were supplied with three NO3-/NH4+ ratios (100/0, 70/30 and 50/50) and exposed to three Cd rates (0.0, 0.5 and 1.0 mmol L-1), being arranged in a randomized complete block design with three replications. Gas exchange parameters, oxidative stress indicators, proline concentration and antioxidant enzyme activities were studied. Exposure to Cd reduced photosynthesis by causing stomatal closure and impairing electron transport. However, the simultaneous supply of NO3- and NH4+, particularly at a 50/50 ratio, restored gas exchange and improved the function of photosystem II, increasing the photosynthetic capacity of the grass. Plants grown with 50/50 showed reduced lipid peroxidation along with increased proline synthesis. Moreover, this NO3-/NH4+ ratio increased the tolerance of tanzania guinea grass to Cd by inducing high superoxide dismutase and glutathione reductase activities in shoots and roots, respectively, maintaining cellular homeostasis and reducing oxidative stress. The negative effects of Cd on photosynthesis and on the balance between oxidants and antioxidants are attenuated by the partial replacement of NO3- by NH4+ in the nutrient solution.

Nitrate and ammonium proportion plays a key role in copper phytoextraction, improving the antioxidant defense in Tanzania guinea grass.

Various nitrate and ammonium proportions (NO3-/NH4+) in the growth media can increase metal phytoextraction compared to supplying solely NO3-. However, there are no studies showing these effects in plants under copper (Cu) contamination as well as their consequences in plant stress tolerance. The objective was to evaluate the effect of NO3-/NH4+ proportions in Cu phytoextraction by Panicum maximum cv. Tanzania and its consequence in the oxidative stress, photosynthesis, and antioxidant system under Cu stress. The experiment was carried out in a randomized complete block design, by using a 3 × 4 factorial with six replications. Three NO3-/NH4+ proportions (100/0, 70/30, and 50/50) were combined with four Cu rates (0.3, 250, 500, and 1000 µmol L-1) in the nutrient solution. It was found that the largest Cu accumulation in the shoots occurred at the first harvest of the plants supplied with 70/30 NO3-/NH4+ and Cu 1000 µmol L-1. Such plants also displayed high concentrations of proline in the shoots as well as high superoxide dismutase activity in the roots. Malondialdehyde concentration was high in the plant parts at the Cu rate of 1000 µmol L-1. Hence, transpiration rates, stomatal conductance, quantum efficiency of photosystem II, electron transport rate, and net photosynthesis were all low at the Cu rate of 1000 µmol L-1. Catalase, guaiacol peroxidase, ascorbate peroxidase, and glutathione reductase activities in the roots were high when plants were exposed to Cu 1000 µmol L-1. In conclusion, the combination of NO3- with NH4+ increases copper phytoextraction that causes oxidative stress, but also favors the antioxidant system of Tanzania guinea grass in attempt to tolerate such stress.

Tropical soils cultivated with tomato: fractionation and speciation of Al.

Soil acidity and the associated problems of aluminum (Al) toxicity and scarce exchangeable bases are typically the most important limiting factors of agricultural yield in wet tropical regions. The goals of this study were to test how soil lime rates affect the forms and distribution of Al in the soil fractions and how different levels of bioavailable Al affect two tomato genotypes grown in wet tropical soils. The tomato genotypes CNPH 0082 and Calabash Rouge were grown in two wet tropical soils in a greenhouse. Soil lime rates of 0, 560, and 2240 mg kg(-1) soil (clay soil) and 0, 280, and 1120 mg kg(-1) soil (sandy soil) were applied to modify Al concentrations. Dry mass production and Al concentrations were determined in shoots and roots. Al was fractionated in the soil, and the soil solution was speciated after cultivation. The Calabash Rouge genotype possesses mechanisms to tolerate Al3+, absorbed less Al, exhibited smaller reduction in growth, and lower Al concentrations in plant parts than the CNPH 0082. Increased soil pH reduced the exchangeable Al fraction and increased the fraction mainly linked to organic matter. Al in the soil in the form of complexes with organic compounds and Al(SO4)+ (at the highest lime rate) did not affect plant development. Soil acidity can be easily neutralized by liming the soil, which transforms toxic Al3+ in the soil into forms that do not harm tomato plants, thereby avoiding oxidative stress in the plants. Al-induced stress in tomatoes varies with genotypes and soil type.

Tropical soils with high aluminum concentrations cause oxidative stress in two tomato genotypes.

Tropical and subtropical soils are usually acidic and have high concentrations of aluminum (Al). Aluminum toxicity in plants is caused by the high affinity of the Al cation for cell walls, membranes, and metabolites. In this study, the response of the antioxidant-enzymatic system to Al was examined in two tomato genotypes: Solanum lycopersicum var. esculentum (Calabash Rouge) and Solanum lycopersicum var. cerasiforme (CNPH 0082) grown in tropical soils with varying levels of Al. Plant growth; activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPOX), and glutathione reductase (GR) enzymes; stress-indicating compounds (malondialdehyde (MDA) and hydrogen peroxide); and morphology (root length and surface area) were analyzed. Increased levels of Al in soils were correlated with reduced shoot and root biomass and with reduced root length and surface area. Calabash Rouge exhibited low Al concentrations and increased growth in soils with the highest levels of Al. Plants grown in soils with high availability of Al exhibited higher levels of stress indicators (MDA and hydrogen peroxide) and higher enzyme activity (CAT, APX, GPOX, and GR). Calabash Rouge absorbed less Al from soils than CNPH 0082, which suggests that the genotype may possess mechanisms for Al tolerance.

Nitrate fertilization enhances manganese phytoextraction in Tanzania guinea grass: a novel hyperaccumulator plant?

Manganese (Mn) is essential for plants but very toxic at high rates. However, hyperaccumulators can tolerate high Mn concentrations in plant tissue, especially when properly fertilized with N. Tanzania guinea grass (Megathyrsus maximus Jacq.) has been indicated as metal tolerant and a good candidate for Mn phytoextraction due to its fast growth and high biomass. The objective was to evaluate the Mn hyperaccumulator potential of Tanzania guinea grass grown as affected by proportions of nitrate/ammonium (NO3-/NH4+). An experiment in a growth chamber with nutrient solution, combining NO3-/NH4+ proportions (100/0 and 70/30) and Mn rates (10, 500, 1500, and 3000 µmol L-1), was carried out. The highest Mn concentration was verified in plants grown with 100/0 NO3-/NH4+ and Mn at 3000 µmol L-1, reaching up to 5500 and 21,187 mg kg-1 in shoots and roots, respectively, an overall concentration of 13,345 mg kg-1. These numbers are typically seen in hyperaccumulators. At that combination, Mn accumulation in shoots was also the highest, reaching up to 76.2 mg per pot, a phytoextraction rate of 23.1%. Excess Mn increased both H2O2 concentration in roots and non-photochemical quenching and therefore decreased net photosynthesis, stomatal conductance, electron transport rate, and photochemical quenching. Nevertheless, proline concentration in roots affected by excess Mn was high and indicates its important role for mitigating stress since Mn rates did not even affect the dry biomass. Tanzania guinea grass is highly tolerant to excess Mn as much as a hyperaccumulator. However, to show all its potential, the grass needs to be supplied with N as NO3-. We indicate Tanzania guinea grass as a Mn hyperaccumulator plant.

Potassium reduces oxidative stress in tanzania guinea grass under cadmium toxicity.

Plants used for phytoextraction of metals need to tolerate toxicity conditions. Potassium (K) participates in physiological and biochemical processes that can alleviate toxicity by heavy metals, including cadmium (Cd). This study aimed to evaluate the effect of K on photosynthesis and on the changes in the antioxidant system of tanzania guinea grass [Panicum maximum Jacq. cv. Tanzania (syn. Megathyrsus maximus (Jacq,) B.K. Simon & S.W.L. Jacobs)] under Cd toxicity. Plants were grown in a greenhouse, in nutrient solution, in a randomized complete block design, arranged in a 3 × 4 factorial, with three replications. Plants were supplied with three K levels (0.4 [K deficiency], 6.0, and 11.6 mmol L-1) and exposed to four Cd levels (0.0, 0.5, 1.0, and 1.5 mmol L-1). Two plant growth periods were evaluated. High Cd level (1.5 mmol L-1) led to a reduction in net photosynthesis (76%) by causing low stomatal conductance and losses in quantum efficiency of photosystem II. However, high K supply (11.6 mmol L-1) increased the net photosynthesis by 15% in plants exposed to 1.0 mmol L-1 Cd, due to upregulation of proline synthesis. Cd toxicity resulted in increases in lipid peroxidation and hydrogen peroxide concentration (35 and 50%; 25 and 30%, at first and second harvest, respectively) and reduction by 80-100% in activity of the antioxidant enzymes: superoxide dismutase, catalase, ascorbate peroxidase, guaiacol peroxidase, and glutathione reductase in the shoots of the grass. However, the high K supply (11.6 mmol L-1) increased the activity of these enzymes (about 50-75%) and reduced lipid peroxidation (36%), restoring cellular homeostasis. Moreover, high K supply promoted a 25% increase in spermidine and spermine concentrations in the shoots. Therefore, K reduced the Cd-induced oxidative stress and increased the net photosynthesis in tanzania guinea grass by increasing the activity of antioxidant enzymes and proline and polyamines synthesis, which enhances the tolerance of this grass to Cd.

Silicon modulates copper absorption and increases yield of Tanzania guinea grass under copper toxicity.

Silicon (Si) is a beneficial element which was proven to enhance the tolerance of plants to excess metal in a given growth medium. However, the efficacy of Si in mitigating Cu toxicity in plants can vary between plant species and with the amount of copper (Cu) present in the soil/medium. An experiment was performed to investigate the role of Si in alleviating Cu toxicity in Tanzania guinea grass (Panicum maximum cv. Tanzania). The experimental design consisted on complete random blocks with tree replicates containing three Si rates (0, 1, and 3 mmol L-1) and four Cu rates (0.3, 250, 500, and 750 µmol L-1). The grass was grown for 62 days in a greenhouse under hydroponic conditions, with a total of 36 pots. Thirteen days after sowing, seedlings were transplanted to pots and grown for further 25 days, and then exposed to the set Cu rates for 7 days. The plants were also evaluated more for 30 days after the first harvesting. The results confirmed that the Si supply to Tanzania guinea grass can alleviate the effects of excessive Cu. Plant yield increased with Si supply and decreased with the increment of Cu rates in both growth periods. Copper concentration in diagnostic leaves (DL) and in roots, and Cu content in shoots and roots were higher in plants exposed to Cu of 750 µmol L-1 with no Si application than in other combinations. Besides reducing Cu concentration in plant tissues, the most important Si role was reducing the transport of Cu from roots to shoots, which allowed successive harvesting. Graphical abstract.

Nitrogen form regulates cadmium uptake and accumulation in Tanzania guinea grass used for phytoextraction.

Plants benefit from the simultaneous uptake of nitrate (NO3-) and ammonium (NH4+), which can influence the bioaccumulation of heavy metals. Nevertheless, there are no studies on the effect of nitrogen forms on grasses used for cadmium (Cd) phytoextraction. The objective was to evaluate the response of Panicum maximum cv. Tanzania to NO3-/NH4+ ratios and Cd levels. A 3 × 3 factorial experiment was conducted under greenhouse conditions, in a randomized complete block design replicated three times, with three NO3-/NH4+ ratios (100/0, 70/30 and 50/50) and three Cd levels (0.0, 0.5 and 1.0 mM). Although it increased plant total nitrogen concentration, Cd exposure reduced shoot and root growth. Moreover, it altered nitrogen metabolism and induced the accumulation of NO3- and NH4+ mainly in shoots. The supply of 50/50 disturbed glutamine synthetase activity and changed root morphology under Cd toxicity. However, while the exclusive use of NO3- mitigated toxicity symptoms, by favoring Cd accumulation in roots and maintaining normal nitrogen metabolism, plants grown with 50/50 showed increased uptake, transport and accumulation of this metal. Thus, Cd uptake and accumulation are strongly related to the form of nitrogen available, and the supply of 50/50 increases the phytoextraction of this metal.

Potassium affects the phytoextraction potential of Tanzania guinea grass under cadmium stress.

The supply of potassium (K) is a strategy to increase the tolerance of plants exposed to Cd toxicity. The aim of this study was to verify the influence of K on the growth and potential of Tanzania guinea grass (Panicum maximum Jacq. cv. Tanzania (syn. Megathyrsus maximus (Jacq.) B.K. Simon & S.W.L. Jacobs)) for Cd phytoextraction as well as to evaluate nutritional attributes of this grass under conditions of Cd stress. The experiment was conducted in a randomized complete block design, using a 3 × 4 factorial arrangement, with three replications. Three rates of K (0.4, 6.0, and 11.6 mmol L-1) were combined with four rates of Cd (0.0, 0.5, 1.0, and 1.5 mmol L-1) in nutrient solution. Two plant growth periods were evaluated. The increase in K supply to plants exposed to Cd rates of up to 1.0 mmol L-1 caused increase in morphogenic and production attributes, as well as reduction in tiller mortality rate, in the second growth period. K concentrations (in both harvests) increased, while calcium and magnesium concentrations in the second harvest decreased with increasing Cd rates. The high availability of Cd (1.5 mmol L-1) in the nutrient solution caused decrease in relative chlorophyll index (RCI) in both harvests. The high supply of K to plants exposed to Cd resulted in high shoot dry mass production, reducing Cd concentration in the photosynthetic tissues (which means great tolerance of the plant) and increasing the accumulation of this metal in the shoots that can be harvested. Therefore, K increases the Cd phytoextraction capacity of Tanzania guinea grass.

NO3-/NH4+ ratios affect nutritional homeostasis and production of Tanzania guinea grass under Cu toxicity.

Nitrogen (N) can alleviate metal toxicity. However, as of yet, there have been no studies showing the efficacy of NO3-/NH4+ 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 NO3- and NH4+ 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 NO3-/NH4+ ratios (100/0, 70/30, and 50/50) and four Cu rates (0.3, 250, 500, and 1000 µmol L-1) in nutrient solution. Copper concentrations in the diagnostic leaves (DL) were highest in plants grown under 70/30 NO3-/NH4+ ratios and a Cu rate of 1000 µmol L-1. In this combination, it was observed that DL had higher concentrations of NH4+, 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 NO3- and 1000 Cu µmol L-1 showed that DL had lower concentrations of Cu, higher concentration of chlorophyll, higher NO3- concentration, higher nitrate reductase activity, and higher NO3- 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 NO3-/NH4+ ratios, and N supply via NO3- allowed for better homeostasis of the forage grass.

NO3-/NH4+ proportions affect cadmium bioaccumulation and tolerance of tomato.

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 (NH4+), nitrate (NO3- ), and many other water-soluble compounds such as urea and amino acids, and nourishing plants with N, providing part of it as NH4+, is an interesting alternative to the supply of this nutrient in the exclusive form of NO3- under Cd toxicity. The objective was to evaluate the influence of NO3- /NH4+ 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-1) and three NO3-/NH4+ 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-1) tested in the growth medium, whereas the NO3- /NH4+ proportions and other Cd rates did not significantly influence this variable. The lowest SPAD values were observed at the 100/0 NO3- /NH4+ proportion and in plants exposed to Cd. The largest accumulation of the metal occurred in the shoots at the NO3- /NH4+ proportion of 70/30 and at 100 µmol L-1 Cd and in the roots at 100/0 NO3-/NH4+ and with 50 and 100 µmol L-1 Cd. The concentration and accumulation of NO3- were highest at the NO3-/NH4+ proportion of 100/0 in the shoots and at 50/50 NO3-/NH4+ in the roots, whereas for NH4+, values were higher as the proportion of N supplied in the form of NH4+ 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 NO3-/NH4+ 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 NO3-/NH4+ 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.