Kinetic modeling indicates changes in the soil quality of agroecosystems in the Brazilian Cerrado

Abstract

Enzyme kinetic parameters provide precise soil quality information about the entire catalytic process caused by land-use change. This study aimed to determine a mathematical model capable of estimating kinetic parameters of hydrolases and oxidoreductases related to soil quality indicators in crop-livestock-forest system (CLF), old pasture, and a native ecosystem of the Brazilian savannah (Cerrado). Soil samples were collected at 0.10 m soil depth and the activity of β-glucosidase, acid phosphatase and phenoloxidase were determined. Kinetic parameters (Vmax and Km) were calculated using four different mathematical equations, and the substrate affinity and specificity (Ka) were estimated. The Hanes-Woolf equation exhibited a greater adjustment (R 2 > 0.9) for β-glucosidase, acid phosphatase, and phenoloxidase. The Vmax of β-glucosidase, arylsulfatase and phenoloxidase was higher in CLF, and the Vmax of phosphatase was higher in the old pasture (p < 0.05). The Km values of β-glucosidase and acid phosphatase were lower in the old pasture, and the Km of arylsulfatase, and phenoloxidase were lower in CLF. Higher Vmax values reflect the complexity and abundance of organic matter found in native Cerrado, followed by CLF. The apparent better performance of phosphatase kinetics on old pasture soils demonstrate the competition of soil microorganisms in a low resource environment. The higher the content of soil organic matter, the greater the specificity constant for β-glucosidase and arylsulfatase in the Cerrado. We concluded that the HW equation was more appropriate to estimate enzyme kinetics, as linear model. Additionally, data on this work showed that hydrolases and oxidoreductases are influenced by land-use change.