不同环境因子对多效唑在海南芒果园土壤中降解的影响

多效唑是一种三唑类植物生长调节剂,在海南芒果园使用量大,环境风险高。然而,多效唑在海南芒果园土壤中的降解行为尚不明确。为此,采集海南芒果典型种植区（乐东、东方、昌江）土壤为研究对象,考察了多效唑的本底降解特征,分析了土著微生物、外源铁还原菌、土壤持水量等环境因子对多效唑降解的影响。结果显示：多效唑在海南芒果园土壤中的降解半衰期（t_1/2）为51~114 d,属中等降解或较难降解农药。其中,乐东土壤中的t_1/2最大,残留风险最高。在海南芒果园土壤中,环境因子对多效唑降解的影响与土壤类型密切相关。在乐东土壤中灭杀土著微生物和添加外源铁还原菌对多效唑降解的影响微弱,而在东方土壤和昌江土壤中,灭杀土著微生物可使多效唑的降解速率下降67.47%~69.12%,t_1/2延长2.4~3.0倍,表明多效唑在这2种土壤中的降解主要是微生物参与的生物化学过程。同样,添加外源铁还原菌也抑制了多效唑在这2种土壤中的降解,使t_1/2延长2~4倍,表明胞外电子传递不但未能氧化还原降解多效唑,甚至可能影响土著微生物对多效唑的降解活性。不同土壤持水量的多效唑t_1/2表现为：60%持水量>30%持水量>100%持水量,表明适度的持水量可加速多效唑在土壤中的降解。主成分分析表明,在海南芒果园土壤中,土壤理化性质对多效唑降解的影响大于外部环境因子,其中,pH和阳离子交换量（CEC）是2个关键土壤因子,较低的土壤pH或较高的CEC更有利于多效唑的降解。研究结果可为海南芒果园土壤中多效唑残留的风险预防和管控提供基础数据。

Effects of Different Environmental Factors on Degradation of Paclobutrazol in Mango Plantation Soil in Hainan

Paclobutrazol, as a triazole plant growth regulator, is largely used in mango plantation soil in Hainan province and has high environmental risk in soil. However, the degradation of paclobutrazol in Hainan mango plantation soil is still unclear. This becomes the barriers to predict the bioavailability, toxicity and environmental risk of paclobutrazol in soil. Therefore, three typical soils were chosen in Hainan mango orchard, including Ledong soil, Dongfang soil, and Changjiang soil. Moreover, the degradation characteristics of patrabutrazol in the background soil and the effects of environmental factor were investigated by a microcosm experiment combined with chemometrics modeling. Three environmental factors were explored in this study, including indigenous soil microorganisms, the addition of iron-reducing bacteria, and soil humidity. Results showed that the degradation half-life (t_1/2) of paclobutrazol in the soil of Hainan mango plantation ranged from 51 d to 114 d, which indicated that paclobutrazol was a refractory or moderately refractory pesticide in Hainan mango plantation soil. In which, the t_1/2 value was largest in Ledong soil, implying the highest residual risk. The effects of environmental factors on paclobutrazol degradation in Hainan Mango plantation soil were closely related to the soil types. The effects of extermination of indigenous microorganisms and the addition of exogenous iron-reducing bacteria on paclobutrazol degradation in Ledong soil were negligible. However, for the Dongfang soil and Changjiang soil, the degradation rate of paclobutrazol decreased by 67.47% and 69.12% respectively, without autochthonous bacteria, and its t_1/2 values were extended by 2.4 and 3.0 times, respectively. These results indicated that the degradation of paclobutrazol in two soils was mainly through a biochemical process by microorganisms. Similarly, the addition of iron-reducing bacteria inhibited the degradation of paclobutrazol in both two soils, and prolonged the t_1/2 by 2 and 4 times, respectively. This result suggested that the extracellular electron transport not only could not degrade paclobutrazol through oxidoreduction in soil, but also affected the activity of indigenous soil microorganism. The t_1/2 values of paclobutrazol under different soil humidity were in the order of 60% > 30% > 100%. This indicated that soil with moderate humidity was beneficial for the degradation of paclobutrazol in Hainan mango plantation soil. Principal component analysis showed that the effects of soil properties on paclobutrazole degradation were greater than that of external environmental factors. In which, cation exchange capacity (CEC) and pH were the two key factors. The soil with high pH value and large CEC were more conducive to the degradation of paclobutrazol in Hainan mango plantation soil. The findings will provide a scientific basis for the prevention and control of the residual risk of paclobutrazol in mango orchard soil in Hainan.