摘要:草甘膦农药的大量喷施，使其在环境特别是土壤中的残留-累积风险日益突出，从团聚体粒径角度研究红壤不同粒径团聚体中草甘膦的降解动力学及其相互作用特征仍鲜有报道。基于此，本研究通过干筛筛分、室内控制培养、液质联用定量分析相结合等探究草甘膦降解残留，并进一步分析团聚体理化性质与草甘膦降解的关系。结果表明：1）不同粒径团聚体中，草甘膦残留量随降解时间不断减小，且粒径之间降解动力学差异不显著。降解半衰期为15.8~20.6 d，粒径最小的团聚体（< 0.25 mm）中草甘膦的降解半衰期最长，为20.6 d。草甘膦在土壤中的主要降解产物氨甲基磷酸（AMPA）的含量随着降解时间的增加而增加，且在第5 d达到峰值，而后不断减小；不同粒径团聚体间AMPA含量差异显著（P < 0.05）。2）相关分析及主成分分析发现，草甘膦残留量与红壤团聚体中速效磷含量呈显著正相关（P < 0.05），而其降解产物AMPA含量与团聚体中酸性磷酸酶活性及N-乙酰氨基-β-葡萄糖苷酶活性呈显著正相关（P < 0.05）。团聚体粒径与草甘膦残留量间没有显著相关性，但与AMPA含量显著正相关（P < 0.05）。此外，草甘膦降解过程中，团聚体中有机质含量及β-葡萄糖苷酶、N-乙酰氨基-β-葡萄糖苷酶、酸性磷酸酶活性与团聚体粒径为显著负相关关系（P < 0.05）。由此表明：红壤不同粒径团聚体影响草甘膦降解速率，粒径最小的团聚体（< 0.25 mm）中草甘膦农药的降解速率最慢，但试验结束时，各粒径红壤团聚体中的草甘膦和AMPA含量均较高，可能会影响土壤健康及生态环境安全；此外，草甘膦降解与土壤磷素密切相关，后续研究需探讨磷亏缺或丰盈条件下，草甘膦农药的土壤环境特征，为后续农田草甘膦环境风险评估提供依据。
关键词:土壤团聚体/
草甘膦/
降解动力学/
土壤磷/
红壤
Abstract:With intensive glyphosate application, its residues and consequent risks of soil health and ecological environment safety have received greater attention. The degradation kinetics of glyphosate in red soil aggregates with different sizes, as well as the interaction between physical and chemical properties of soil aggregates and the degradation of glyphosate, have rarely been studied. Thus, in this study, the degradation characteristics of glyphosate in red soil aggregates with different sizes were observed under laboratory conditions by particle pre-sieving, incubation in a controlled climatic chamber, and residue analysis via liquid chromatography-tandem mass spectrometry. The physical and chemical properties of the soil aggregates, such as contents of organic matter, total phosphorus, and available phosphorus, were tested according to the national approved methods and standards. The relationships between the physical and chemical properties of the aggregates and the degradation of glyphosate were further analyzed and compared in the same observation day. The results showed that 1) the glyphosate content decreased in the different aggregate particles during the observation period, following the single first-order kinetic degradation model. However, no significant differences were observed among different aggregate sizes. The half-life time of glyphosate in the different red soil aggregates ranged from 15.8 to 20.6 d, with a longer half-life time in the smallest aggregates (< 0.25 mm, 20.6 d). The aminomethylphosphonic acid (AMPA) content, the main metabolite of glyphosate, increased immediately and peaked on the 5th day after glyphosate application, but no differences were found among different aggregates. However, the AMPA content changed and declined significantly in different aggregates after the 5th observation day (P < 0.05). The contents of organic matter, total nitrogen, total phosphorus, and available phosphorus in different aggregates varied greatly, especially the available phosphorus content, which decreased with glyphosate degradation. 2) Correlation analysis and principal component analysis of glyphosate, aggregate size, and their properties showed that the residual glyphosate was significantly positively correlated with the content of available phosphorus (P < 0.05), and the AMPA content was significantly positively correlated with the activities of acid phosphatase and N-acetylamino-β-glucosidase (P < 0.05). There were no significant relationships between the aggregate size and the residuals of glyphosate, but a significant positive correlation was observed between the aggregate size and the AMPA content (P < 0.05). Furthermore, during the whole period of glyphosate degradation, the organic matter content, acid phosphatase, N-acetylamino-β-glucosidase, and β-glucosidase showed a significant negative relationship with the soil aggregate size (P < 0.05). In conclusion, the characteristics of the red soil aggregates affect the degradation kinetics of glyphosate, as well as the persistence of AMPA, especially the residuals in the smallest aggregates (< 0.25 mm). The contents of glyphosate and AMPA in the red soil aggregates were still high after 30 days, which may affect soil health. Glyphosate degradation was also closely related to phosphorus in the soil. Therefore, the fate of glyphosate under conditions of phosphorus deficiency or abundant soil should be explored to provide detailed information on glyphosate risk assessment in red soil.
Key words:Soil aggregates/
Glyphosate/
Degradation kinetics/
Soil phosphorus/
Red soil
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