Efeito da sazonalidade sobre a atividade enzimática em solos do cerrado goiano

Abstract

Monitoring of seasonal enzyme activity may constitute a mechanism to assess the fertility of soil, or the state of their biological activity throughout the year. The enzyme β-glucosidase (EC 3.2.1.21) is found in most soils and is involved in the degradation of cellulose derivatives. For their abundance, this enzyme is considered as an indicator of the quality of the soil. Phosphatases (EC 3.1.3) are fundamental in phosphorus mineralization and hence the cycling of this nutrient in the environment. They are widely distributed in the soil, and have been widely studied because they catalyze the hydrolysis of organic phosphorus to inorganic phosphorus, thus making it available to plants. The enzymes phenol oxidase (EC 1.14.18.1) and peroxidase (EC 1.11.1.7) play key roles in the ecosystem, such as lignin degradation, humification, mineralization of carbon and degradation of organic pollutants. The objective of this study was to understand the influence of seasonality and different land use class on activity of hydrolases and oxidoreductases present in soils of Cerrado in Goiás. The study was conducted in the Interpretative Trail of Environmental Education "Trilha do Tatu" located at The Academic Unit of Exact and Technological Sciences (UnUCET) at the State University of Goiás (UEG) in Anápolis-GO. Soil samples were collected at different times of the year, during the period of November 2012 to July 2013, in the layers of 0-15 cm, in the following environments: Cerrado "ss", mesophytic forest and pasture. The map of land cover and land use and the values of rainfall and vegetation index were obtained from the databases of the National Aeronautics and Space Administration, USA (NASA) and the State System of Statistical and Geographical Information of Goiás, Brazil (SIEG). There were held the following physicochemical properties: pH, texture, color, organic matter and chemistry composition. The enzymatic activity of the hydrolase was determined using methods based on colorimetric determination of p-nitrophenol formed after the addition of specific colorless substrate. The enzymatic activity of the oxidoreductases was determined by monitoring 3-dihydroindole-5,6-quinone-2-carboxylate Methyl (DIQC) formed after adding the specific substrate, with and without the addition of H2O2. The analysis of variance (ANOVA Three- way) was performed to test the effect of variables, followed by Tukey test for comparison of means (P < 0.05). The rainfall data of the study area show the presence of two well defined periods in the Cerrado: dry and rainy, which have a direct influence on the vegetation index. Significant differences were observed in the activity of the enzyme α and β-glucosidase during the year between the classes of land use analyzed. The soils collected in the rainy season showed greater activity of the two enzymes. It was observed that the higher the carbon content in the soil, the higher are the values of α and β-glucosidase activity. Divalent ions, such as calcium and magnesium, probably play important roles in enzymatic catalysis, acting as co-factors or activators. The activity of acid phosphatase in soils of Cerrado "ss" remained constant, however, presented significant difference between the dry and rainy seasons in regions of mesophytic forest and pasture. Acid phosphatase was rigorously controlled by the biological demand, with lower activity when phosphate was abundant. The enzyme phenoloxidase showed no significant correlation with any of the factors analyzed, however, its activity varied significantly throughout the year in Cerrado "ss" soils. The activity of the enzyme peroxidase was statistically higher in areas of Cerrado “ss” throughout the year. The physico-chemical composition of the soil, the presence of inducers of gene expression and enzyme activators exerted great influence on the activity of this enzyme.