Atividade e modelagem de fosfatase do solo como indicadores em agroecossistemas no cerrado

Abstract

Soil phosphatase is a primary indicator of soil quality and its activity plays a key role on productivity of terrestrial ecosystems. Modelling the kinetic parameters of soil phosphatase is central to integrate ecological processes in tropical soils under different land use ecosystems. The goal of this study was to determine kinetic parameters of acid soil phosphatase in surface layers (depth at the 0-5cm and 5-10 cm) from an Oxisol under the Cerradão, pine, soya and sugarcane ecosystems. Acid soil phosphatase activity was performed with different substrate concentrations (0, 0.5, 1, 2, 4, 8 and 16 µmol of p-nitrophenol phosphate) at 37oC, pH 6.5 and acetate buffer. The kinetic parameters (Km and Vmax) were estimated using Michaelis-Menten and Eadie-Hofstee equations. Soil organic carbon (SOC), total nitrogen (TN), soil microbial respiration (SMR), microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN), and dehydrogenase activity were also measured. In both models, the highest Vmax and Km values were found in native Cerrado soil, following the pine soil in two surface layers. Soya and sugarcane soils presented low Km values, showing a great substrate affinity of soil phosphatase in theses ecosystems. Michaelis-Menten model estimated higher Vmax and Km values than Eadie-Hofstee model. Michaelis-Menten model did not show no difference of Km between two layers of ecosystems, but Eadie-Hofstee model reveled significant differences between layers as the least Km values at the 5-10 cm. Results reveled that Km has a significant correlation with SOC (r > 0.71), TN (r > 0.72), MBC (r > 0.75) and MBN (r > 0.75). Results also showed a greater correlation between Km of Eadie-Hofstee model and soil quality indicators than Michalis-Menten model, suggesting that Eadie-Hofstee model may improve the relationship between soil ecological processes. Our study shows the importance of modelling the acid soil phosphatase in the Brazilian Cerrado in relation to land use ecosystems, depths and model applied.