Influence of short-time imidacloprid and acetamiprid application on soil microbial metabolic activity and enzymatic activity
2014
Wang, Fei | Yao, Jun | Chen, Huilun | Yi, Zhengji | Choi, Martin M. F.
The influence of two neonicotinoids, i.e., imidacloprid (IMI) and acetamiprid (ACE), on soil microbial activities was investigated in a short period of time using a combination of the microcalorimetric approach and enzyme tests. Thermodynamic parameters such as QT(J g⁻¹soil), ∆Hₘₑₜ(kJ mol⁻¹), JQ/S(J g⁻¹ h⁻¹), k (h⁻¹), and soil enzymatic activities, dehydrogenase, phosphomonoesterase, arginine deaminase, and urease, were used to evaluate whole metabolic activity changes and acute toxicity following IMI and ACE treatment. Various profiles of thermogenic curves reflect different soil microbial activities. The microbial growth rate constant k, total heat evolution QT(expect for IMI), and inhibitory ratio I show linear relationship with the doses of IMI and ACE. QTfor IMI increases at 0.0–20 μg g⁻¹and then decreases at 20–80 μg g⁻¹, possibly attributing to the presence of tolerant microorganisms. The 50 % inhibitory ratios (IC₅₀) of IMI and ACE are 95.7 and 77.2 μg g⁻¹, respectively. ACE displays slightly higher toxicity than IMI. Plots of k and QTagainst microbial biomass-C indicate that the k and QTare growth yield-dependent. IMI and ACE show 29.6; 40.4 and 23.0; and 23.3, 21.7, and 30.5 % inhibition of dehydrogenase, phosphomonoesterase, and urease activity, respectively. By contrast, the arginine deaminase activity is enhanced by 15.2 and 13.2 % with IMI and ACE, respectively. The parametric indices selected give a quantitative dose-response relationship of both insecticides and indicate that ACE is more toxic than IMI due to their difference in molecular structures.
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