3 research outputs found
Study of mineralization, degradation, sorption-desorption and leaching of the herbicide aminocyclopyrachlor in Brazilian soils
O aminociclopiraclor é o primeiro herbicida sintetizado do grupo químico ácido pirimidinocarboxílico, pertence à classe das auxinas sintéticas, atua em um amplo espectro de plantas daninhas, e está em fase de registro junto a ANVISA. A literatura sobre o aminociclopiraclor ainda é limitada, mas sabe-se que suas principais vantagens são o amplo espectro de controle de plantas daninhas, elevada eficácia em baixas doses de aplicação, e baixa toxicidade a organismos não alvo. Estudos como degradação, sorção - dessorção e lixiviação de herbicidas em diferentes tipos de solos são indispensáveis para revelar a dinâmica do seu comportamento no solo promovendo subsídios para evitar efeitos prejudiciais ao ambiente e as culturas subsequentes. O presente trabalho teve como objetivo a avaliação da dinâmica do herbicida aminociclopiraclor através de ensaios de degradação e mineralização, sorção-dessorção e lixiviação em três solos brasileiros: Latossolo Vermelho distrófico (LVd - textura arenosa), Plintossolo Pétrico concrecionário (FFc - textura argilosa) e Latossolo Vermelho eutrófico (LVe - textura muito argilosa). Os estudos foram realizados no Laboratório de Ecotoxicologia do CENA/USP seguindo as normas da \"Organisation For Economic Co-operation and Development\" (OECD). As taxas de mineralização do aminociclopiraclor nos solos avaliados foram inferiores a 10%, e seguem a seguinte ordem: FFc < LVd < LVe. A concentração extraível do aminociclopiraclor foi reduzida em 37% após 126 dias, indicando a tendência à formação de resíduos ligados. O sistema de eluição utilizado na técnica de cromatografia em camada delgada não foi adequado para separar e qualificar a presença de metabólitos extraíveis. O modelo de Freundlich apresentou ajuste adequado para a sorção e dessorção do aminociclopiraclor, com coeficientes de correlação superiores a 0,99 para os três solos avaliados. Os coeficientes de sorção variaram entre 0,37 e 1,34 enquanto os de dessorção variaram entre 3,62 a 5,36. Os coeficientes de sorção apresentam correlação positiva significativa com os teores de argila, o mesmo comportamento não foi verificado em relação ao pH. Nos solos de textura argilosa (FFc e LVe), o aminociclopiraclor apresentou médias de lixiviação inferiores a 1%, e no solo de textura arenosa (LVd) superior a 3%. As concentrações do herbicida na primeira camada do solo (0-5 cm) apresentaram correlação positiva significativa com os teores de argila e capacidade de troca catiônica, o mesmo não foi observado em relação a matéria orgânicaThe aminocyclopyrachlor is the first herbicide of the chemical group pyrimidinecarboxylic acid, belongs to the class of synthetic auxin, acts in a broad spectrum of weeds and is under registration at ANVISA. The literature on the aminocyclopyrachlor is still limited, but it is known that its main advantages are the broad spectrum of weed control, high efficacy at low application rates, and low toxicity to non-target organisms. Studies such as degradation, sorption-desorption and leaching of herbicides in different types of soils are essential to reveal the dynamics of its behavior in the soil promoting subsidies to avoid adverse environmental effects and the subsequent cultures. This study aimed to evaluate the dynamics of herbicide aminociclopiraclor by testing degradation and mineralization, sorption-desorption and leaching in three Brazilian soils: Latossolo Vermelho distrofico (LVd - sandy texture), Plintossolo Petrico concrecionãrio (FFc - clay texture) and Latossolo Vermelho eutrofico (LVe - clay texture). The studies were conducted at the Laboratory of Ecotoxicology CENA/USP, following the rules of the Organisation For Economic Co-operation and Development (OECD). Mineralization rates in the aminocyclopyrachlor evaluated soils were lower than 10%, and follow the following order: FFc <LVd <LVe. The concentration of extractable aminocyclopyrachlor was reduced by 37% after 126 days, indicating the tendency to formation of bound residues. The system elution technique used in thin layer chromatography was inadequate to separate and qualify the presence of extractable metabolites. The Freundlich model showed an adequate fit for the sorption and desorption of aminocyclopyrachlor, with correlation coefficients higher than 0.99 for the three test soils. The sorption coefficients ranged from 0.37 to 1.34 while the desorption ranged from 3.62 to 5.36. The sorption coefficients showed a significant positive correlation with the clay, the same behavior was not observed in relation to pH. In clay soils (FFc and LVe), the aminocyclopyrachlor presented averages less than 1% leaching, and sandy soil (LVd) exceeding 3%. The concentrations of the herbicide in the topsoil (0-5 cm) showed significant positive correlation with clay content and cation exchange capacity, the same was not observed for organic matte
Changes in γ-aminobutyric acid concentration, gas exchange, and leaf anatomy in Eucalyptus clones under drought stress and rewatering
Drought stress promotes biochemical and physiological alterations in plant metabolism that limit growth and yield. This study investigated the accumulation of γ-aminobutyric acid (GABA) in plant tissue, the stomatal conductance (gs) and changes in leaf anatomy in Eucalyptus following drought stress situation. In this study, eight Eucalyptus clones were evaluated under normal water supply (control) and drought stress conditions (stress). For the control treatment, plants were irrigated every day with an automated system until the soil was saturated, and for the stress treatment, drought stress was imposed by non-irrigation of plants, and pots were covered using plastic sheeting to avoid rainfall and humidity. This study has shown that: (1) all clones decreased gs with increasing vapor pressure deficit (D) in both treatments. All plastics and drought-tolerant clones (except GG) presented lower stomatal sensitivity to D under stress conditions than drought-sensitive clones; (2) GABA concentrations increased fast after drought stress, but we could not find correlation with these changes and resistance to water stress; and (3) all clones increased the number of stomata and reduced leaf thickness after water stress. The finding is that GABA is a fast stress-signaling molecule in Eucalyptus, but the response of gs to D is a best physiological variable to differentiate drought-tolerant and drought-sensitive Eucalyptus clones