Effects of fluazinam on soil sucrase activitiy and respiration

Despite beneficial impacts such as improving and sterilizing agricultural products via pest and disease control, pesticide pollution of soils continues to be a huge and growing environmental problem. Repeated and extensive application of pesticides ultimately percolates into the soil, which in turn interact with soil organisms and affect their metabolic activities. Biological activities under continuous pesticide inputs constitute an important aspect of agro-ecological research. To better understand the potential environmental risks of pesticide fluazinam on soil microbial activity and soil quality, the residues and degradation dynamics of fluazinam in soils were determined in a laboratory simulation method. The effects of fluazinam pollution on soil basal respiration, and kinetic and thermodynamic parameters of sucrase were analyzed. Significant fluazinam degradation rates were noted under higher application rates of fluazinam. The half-life of soil fluazinam degradation was 0.38~0.59 d. With increasing concentrations of fluazinam (50 mg·kg^-1, 100 mg·kg^-1 and 1 000 mg·kg^-1), the degrees of inhibition effect on sucrase activity increased. However, inhibition-activation-inhibition curves were fitted at lower concentration (1 mg·kg^-1, 5 mg·kg^-1) treatments with large ranges of fluctuating. 10 mg·kg^-1 of fluazinam initially inhibited and later enhanced soil sucrase activity with a great fluctuation. The maximum rate of enzymatic reaction (V_max) of sucrase was noted along with different Michaelis constant (K_m) under different fluazinam concentrations. The activation energy (E_a) of sucrose was higher under 1 mg·kg^-1 fluazinam than that under the control (CK), but lower under other fluazinam concentrations than under CK. Activation enthalpy change (ΔH) decreased with increasing fluazinam concentrations (from 5 mg·kg^-1 to 1 000 mg·kg^-1). Sucrase activation entropy change (ΔS) under fluazinam concentration of 1 mg·kg^-1 was lower than under CK for the same temperature conditions, though insignificant changes in free energy of activation (ΔG). The maximum velocity constant (Q₁₀) was in the thermodynamic temperature range of 320~330 K, and minimum in 290~300 K. Soil microbial basal respiration initially decreased, followed by a increase under lower fluazinam concentration treatments. However, inhibition effects were noted in higher concentration treatments all through incubation period. The findings had useful applications in future research on enzymatic mechanisms in relation to pesticides pollution and soil integrity.