兽用抗生素磺胺二甲嘧啶对稻田N2O排放的影响及其微生物机制

为研究磺胺类兽用抗生素对稻田N_2O排放的影响及其微生物机制,采用田间原位观测试验,对比分析不同浓度磺胺二甲嘧啶(sulfamethazine,SMZ)对稻田N_2O排放及硝化反硝化过程底物和相关功能基因丰度的影响.本试验共设5个处理,分别为:无肥料无抗生素(CK);猪粪为基肥,尿素为追肥,分别添加0、5、15和30 mg·kg~(-1)的SMZ处理(SMZ0、SMZ5、SMZ15和SMZ30),在整个水稻生长季定期采集和分析土壤和气体样品.结果表明,不同浓度SMZ均未改变稻田N_2O排放的季节性规律,整个观测期N_2O排放通量,与SMZ0处理相比,SMZ15有显著差异(P 0. 05),SMZ30和SMZ5无显著差异(P 0. 05).中、高浓度处理SMZ15和SMZ30在均值水平上增加了N_2O累积排放量,分别是SMZ0处理的3. 47和4. 67倍,且增加了土壤NO_3~--N含量.与SMZ0处理相比,中、高浓度处理对土壤总细菌16S rRNA基因丰度、硝化过程中氨氧化古菌AOA amoA和氨氧化细菌AOB amoA基因丰度以及反硝化过程中的nirK、nirS和nosZ基因丰度均有明显的激活作用(P 0. 05),低浓度处理SMZ5对各基因丰度则有轻微抑制作用.具体表现为SMZ30、SMZ15与SMZ0处理的16S rRNA、AOA amoA、AOB amoA以及nirK、nirS、nosZ基因丰度比值的平均值分别为:1. 58、1. 77、2. 15、1. 38、1. 33、1. 42和1. 24、1. 37、1. 08、1. 65、1. 11、1. 64,而SMZ5与SMZ0处理的6个上述基因丰度比值均小于1,仅分别为0. 80、0. 99、0. 92、0. 76、0. 76和0. 77. N_2O排放通量与nir K基因丰度呈极显著正相关(P 0. 01),表明SMZ通过影响反硝化菌活性进而对N_2O排放产生作用.因此,兽用抗生素对农田的污染不可忽视,应从源头上合理控制使用,以减少其环境生态风险.

Effects of the Veterinary Antibiotic Sulfamethazine on N2O Emissions and the Associated Microbiological Mechanism in a Rice Field

Veterinary antibiotics can enter into croplands with animal excrement and can have effects on nitrification and denitrification processes in the agricultural soils. A field experiment was conducted to evaluate the effect of sulfamethazine (SMZ) on N₂O emissions, nitrification, denitrification, and related functional gene abundances within a paddy field. Five treatments were used in the experiment, namely, no fertilizer and no antibiotics applied (CK), and pig manure used as basal fertilizer plus urea applied as topdressing with the addition of 0, 5, 15, and 30 mg·kg^-1 SMZ (SMZ0, SMZ5, SMZ15, and SMZ30, respectively). Soil and gas samples were collected and analyzed periodically throughout the rice growing season. The results showed that the SMZ did not change the seasonal pattern of N₂O emissions. During the entire observation period, there was a significant difference in N₂O fluxes between the SMZ15 and SMZ0 treatment (P<0.05), but there was no significant differences in N₂O fluxes between the SMZ30, SMZ5, and SMZ0 treatment (P>0.05). Medium and high concentrations (SMZ15, SMZ30) increased the cumulative emissions of N₂O at the average level, and these values were 3.47 and 4.67 times higher than that of the SMZ0 treatment, respectively; the soil NO₃^--N content also increased. Medium and high concentrations had a significant activation effect on the gene abundances of total soil bacteria 16S rRNA, ammonia-oxidizing archaea (AOA) amoA, and ammonia-oxidizing bacteria (AOB) amoA during the nitrification process and the gene abundances of nirK, nirS, and nosZ during the denitrification process (P<0.05), while the SMZ treatment with a low concentration had a slight inhibitory effect on the abundance of each gene. The ratios of abundance copies of 16S rRNA, AOA amoA, AOB amoA, and the genes of nirK, nirS, and nosZ treated by SMZ30, SMZ15, and SMZ0 were 1.58, 1.77, 2.15, 1.38, 1.33, 1.42, and 1.24, 1.37, 1.08, 1.65, 1.11, 1.64, respectively, at the average level. The abundance ratios of the six above genes treated by SMZ5 and SMZ0 were less than one and only 0.80, 0.99, 0.92, 0.76, 0.76, and 0.77, respectively. The N₂O fluxes were significantly and positively correlated with the abundances of the nirK gene (P<0.01), thus indicating that SMZ had an effect on N₂O emissions by influencing the activity of denitrifying bacteria. Therefore, the pollution of farmland by veterinary antibiotics should not be ignored, and the use of antibiotics should be controlled reasonably at the source, so as to reduce the environmental and ecological risks.