Interploidy hybridization in sympatric zones: the formation of Epidendrum fulgens x E. puniceoluteum hybrids (Epidendroideae, Orchidaceae)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Mating system variation and assortative mating of sympatric bromeliads (Pitcairnia spp.) endemic to neotropical inselbergs

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Soil Solution as Affected by Plant Residues and Nitrogen Rates

Cation mobility in acidic soils with low organic-matter contents depends not only on sorption intensity but also on the solubility of the species present in soil solution. In general, the following leaching gradient is observed: potassium (K+) magnesium (Mg2+) calcium (Ca2+) aluminum (Al3+). To minimize nutrient losses and ameliorate the subsoil, soil solution must be changed, favoring higher mobility of M2+ (metal ions) forms. This would be theoretically possible if plant residues were kept on the soil surface. An experiment was conducted in pots containing a Distroferric Red Latosol, with soil solution extractors installed at two depths. Pearl millet, black oat, and oilseed radish residues were laid on the soil surface, and nitrogen (as ammonium nitrate) was applied at rates ranging from 0 to 150mgkg-1. Corn was grown for 52 days. Except for K+ and ammonium (NH4 +), nitrogen rates and plant residues had little effect upon the concentrations and forms of the elements in the soil solution. Presence of cover crop residues on soil surface decreased the effect of nitrogen fertilizer on Ca leaching. More than 90% of the Ca2+, Mg2+, and K+ were found as free ions. The Al3+ was almost totally complexed as Al(OH3)0. Nitrogen application increased the concentrations of almost all the ions in soil solution, including Al3+, although there was no modification in the leaching gradient.

Evaluation of sample preparation procedures and krypton as an interference standard probe for arsenic speciation by HPLC-ICP-QMS

Different conditions of extraction using water, a methanol-water mixture and nitric acid solutions were evaluated for speciation of As(iii), As(v), DMA and MMA in plant samples that previously received As(v) after being sown and emergence was investigated. Microwave-assisted extraction (MAE) using diluted nitric acid solutions was also performed for arsenic extraction from chicken feed samples. The separation and determination of arsenic species were performed using HPLC-ICP-MS. The interference standard method (IFS) using 83Kr+ as the IFS probe was employed to minimize spectral interferences caused by polyatomic species, such as 40Ar 35Cl+. The extraction procedures tested presented adequate extraction efficiencies (90%), and the four arsenic species evaluated were found in plant samples. Extractions with diluted nitric acid solution at 90 °C were the most efficient strategy, with quantitative recoveries for all four As species in plant tissues. On the other hand, the methanol-water mixture was the solvent with the lowest extraction efficiency (50-60%). For chicken feed samples, MAE at 100 °C for 30 min resulted in an extraction efficiency of 97% and only As(v) was found, without any species interconversion. The IFS method contributed to improving precision and limits of detection and quantification for all tested extraction procedures. Significant improvements on accuracy were obtained by applying the IFS method and recoveries between 77 and 94%, and 82 and 93% were obtained for plant extracts and chicken feed samples, respectively. This journal is © 2013 The Royal Society of Chemistry.