氟啶胺对土壤中蔗糖酶活性及呼吸作用的影响

Effects of fluazinam on soil sucrase activitiy and respiration

使用农药控制作物害虫和疾病可提高农业生产力,然而农药的使用对土壤造成的污染已成为巨大且日益严重的问题。重复、广泛使用的农药进入土壤影响土壤生物、生物代谢及其生物活性,已成为农业生态环境重要的研究内容。为了更好地了解氟啶胺对土壤微生物活性和土壤质量等潜在环境危险,采用实验室模拟的方法研究了氟啶胺农药残留动态,以及氟啶胺对土壤呼吸强度、蔗糖酶活性及其动力学和热力学特征参数的影响。结果表明:高剂量(100 mg.kg-1)氟啶胺在土壤的降解速率常数最大,氟啶胺在土壤中的半衰期范围为0.38～0.59 d。高剂量(50 mg.kg-1、100 mg.kg-1和1 000 mg.kg-1)氟啶胺对土壤蔗糖酶表现出不同程度的抑制作用;低剂量(1 mg.kg-1、5 mg.kg-1)处理表现为抑制-激活-抑制作用,且波动范围较大;10 mg.kg-1氟啶胺对土壤蔗糖酶前期表现为抑制、后期表现为激活作用,波动范围较大。不同浓度氟啶胺胁迫下蔗糖酶促反应的Michaelis常数(Km)和最大反应速率(Vmax)发生改变,但变化不大。土壤中氟啶胺浓度为1 mg.kg-1时蔗糖酶所需的活化能(Ea)比CK高,其他浓度都低于CK;5 mg.kg-1、10 mg.kg-1、50 mg.kg-1、100 mg.kg-1和1 000 mg.kg-1所需的活化焓变(ΔH)随氟啶胺的浓度降低而变小;在相同温度下蔗糖酶的活化熵变(ΔS)表现为:1 mg.kg-1<CK;活化自由能(ΔG)变化差异较小;320～330 K(开氏温度)时最大速度常数(Q10)最大,而290～300 K时Q10较小。低剂量氟啶胺对土壤微生物呼吸作用的影响表现为随时间变化呈现抑制-激活趋势,高低剂量表现为抑制作用。土壤微生物的呼吸活性因氟啶胺的加入而产生波动。本研究结果有助于进一步分析研究受农药污染土壤的质量和酶活之间的相关性。

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 activi-ties 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 maxi-mum rate of enzymatic reaction（Vmax） of sucrase was noted along with different Michaelis constant（Km） under different fluazinam concentrations.The activation energy（Ea） 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.