Vermicompost improves maize, millet and sorghum growth in iron mine tailings.

The Fundão dam was designed to store iron mine tailings in the region of Mariana, MG, Brazil. When it ruptured, the tailings overflowed. These tailings affected the soil due to the formation of a thick crust as a result of drying (compaction) and hindered the natural revegetation process. In this context, the use of organic fertilizers, including vermicompost, is method of reducing the physical limitations on root growth caused by soil properties and changing soil-metal interactions. For this reason, vermicompost was added to iron mine tailings, and its morphological and physiological effects on maize, millet and sorghum plants were studied. The experiment was conducted in a greenhouse using 6 dm3 pots. The plants were subjected to three treatments: mine tailings, mine tailings + vermicompost, and a reference soil. From the V3 stage onwards, biweekly growth, leaf gas exchange and chlorophyll fluorescence evaluations were performed. At the end of the experiment, dry biomass and metal, macro- and micronutrient contents were quantified, and the root morphology was evaluated. The tailings created physical limitations on root growth and had low nutrient content as well as high concentrations of chromium, iron and manganese. The addition of vermicompost favored increases in shoot and root dry biomass, increases in root length, volume, surface area and diameter, and the absorption of macro- and micronutrients, which was reflected in the growth of the studied species. In addition, vermicompost led to greater investment in thick and very thick roots, and in general, the plants showed no symptoms of metal toxicity. Considering the characteristics of the studied tailings, it can be concluded that vermicompost favors the growth of plant species and may be a viable method for beginning the recovery process in areas containing iron mine tailings.

Applications of chitosan to the roots and shoots change the accumulation pattern of cadmium in Talinum patens (Talinaceae) cuttings.

Chitosan induces tolerance to abiotic stress agents in plants. However, studies on the different application forms of this biopolymer are limited. This study evaluated the effect of two forms of chitosan application on the morphophysiology of and metal accumulation by Talinum patens cuttings subjected to Cd to develop new cadmium (Cd) decontamination technologies. Cuttings from 75-day-old plants were transferred to a hydroponic system. For 30 days, three Cd concentrations (0, 7, and 14 mg L-1) and three forms of chitosan application (without application, root, and foliar) were applied. The cuttings were tolerant to Cd because the metal did not influence biomass production or photosynthetic efficiency. Neither chitosan application nor Cd increased the modified chlorophyll content and fluorescence parameters. However, foliar chitosan reduced the transpiration rate. At the highest concentration of Cd, the application of chitosan in the root reduced the Mg content of the root system and shoots. The root application of chitosan increased the surface area and volume of thicker roots at the expense of finer ones. The foliar application resulted in greater total root length and surface area, mainly those finer. Furthermore, chitosan applied to the leaves activated catalase in the roots and leaves. In contrast to the root application, foliar application increased the accumulation of Cd in the roots. The action of catalase and the increase of fine roots may have favored a greater absorption of the nutrient solution and Cd in the chitosan foliar application treatment. It is concluded that chitosan foliar spraying can improve Cd rhizofiltration with T. patens.

Do tailings from the Mariana, MG (Brazil), disaster affect the initial development of millet, maize, and sorghum?

The collapse of the Fundão dam in Mariana, MG, in 2015 resulted in the overflow of more than 50 million m3 of mud containing mine tailings, leaving a path of destruction and immeasurable social and environmental consequences. Tailings' chemical and physical assessments revealed the presence of some elements at levels higher than those allowed by Brazilian guidelines. The tailings also showed high density, which restricts vegetation recovery. Therefore, this study aimed to analyze the effects of mud containing mine tailings from the Fundão dam on the germination and initial growth and development of three plant species: millet, maize, and sorghum. These species were cultivated on substrates with five tailings proportions: 0 T (100% sand), 25 T (25% tailings + 75% sand); 50 T (50% tailings + 50% sand); 75 T (75% tailings + 25% sand); and 100 T (100% tailings). In experiment I, the germination and initial growth of seedlings (plants with 1 or none fully expanded leaf) in these substrates were evaluated. In experiment II, growth parameters, photosynthetic efficiency (gas exchange and chlorophyll a fluorescence), metal accumulation, and plant root morphology of the same species were evaluated at the three fully expanded leaves vegetative stage (V3). Overall, the germination of seedlings and the initial growth of the three species analyzed were not affected by the presence of tailings. However, in plants at the V3 stage, morphophysiology variations differed among species, given that their growth, biomass accumulation, and root dynamics were altered. Proportions of tailings in the substrate did not influence the absorption of iron or manganese by the studied plants. At the V3 stage, maize was the most tolerant, with a more robust root system, and showed fewer morphological changes and greater water use efficiency than the other studied species.

Allelochemical Activity of Eugenol-Derived Coumarins on Lactuca sativa L.

Coumarins are widely distributed substances in plant species that promote phytotoxic effects, allowing them to be exploited as herbicides less harmful to the environment, since many invasive species have demonstrated resistance to commercially available products. The derived coumarins used in this study had not been tested in plant models and their effect on plants was unknown. The objective of this study was to evaluate the phytotoxic action of these coumarins in bioassays with Lactuca sativa L., in order to select the most responsive substance whose toxicity was best elucidated by chromosomal complement and enzymatic antioxidant metabolism studies. From the phytotoxicity assays, coumarin 8-methoxy-2-oxo-6-(prop-2-en-1-yl)-2H-chromene-3-carboxylic acid (A1), reported here for the first time, was selected as the most responsive and caused a reduction in the following parameters: number of normal seedlings, fresh biomass, root length and shoot length. Subsequent studies demonstrated that this coumarin is cytogenotoxic due to damage caused to the cell cycle and the occurrence of chromosomal abnormalities. However, it did not interfere with antioxidant enzyme activity and did not cause lipid peroxidation. The changes caused by coumarin A1 described herein can contribute to better understanding the allelochemical actions of coumarins and the potential use of these substances in the production of natural herbicides.

Isolation and evaluation of the antioxidant activity of phenolic constituents of the Garcinia brasiliensis epicarp.

A new glycosylated biflavonone, morelloflavone-4'″-O-ß-d-glycosyl, and the known compounds 1,3,6,7-tetrahydroxyxanthone, morelloflavone (fukugetin) and morelloflavone-7″-O-ß-d-glycosyl (fukugeside) were isolated from the epicarp of Garcinia brasiliensis collected in Brazil. The structures of these compounds were established using 1H and 13C NMR, COSY, gHMQC and gHMBC spectroscopy. The compounds exhibited antioxidant activity. The greatest potency was displayed by morelloflavone (2), with IC50=49.5mM against DPPH and absorbance of 0.583 at 400µg/mL for the reduction of Fe3+. The weakest potency was displayed by 1,3,6,7-tetrahydroxyxanthone (1), with IC50=148mM against DPPH and absorbance of 0.194 at 400µg/mL for the reduction of Fe3+.