Purpose

The excessive use of nitrogen (N) fertilizer in intensive agriculture has increased nitrate leaching into groundwater, but its impacts on N transformation processes and the associated microbial communities in the deep vadose zone remain unclear.

Materials and methods

Soil samples from 0–1050 cm depth were collected from a 20-year field experiment with two N fertilization treatments: 0 (N0) and 600 kg N ha⁻¹ year⁻¹ (N600). Amplicon sequencing and quantitative PCR analyses were performed to profile the vertical distribution of soil microbial communities and denitrification genes.

Results and discussion

The soil microbial community structure and diversity were strongly influenced by soil depth and N fertilization. The 250 cm depth was identified as a threshold depth, as dramatically different microbial communities were found below and above this depth. Quantitative PCR results showed that the absolute abundance of denitrification genes decreased with increasing soil depth.

Conclusion

This study elucidated the profound effects of long-term N input on the composition and diversity of the microbial communities and the abundance of denitrifiers in the deep vadose zone. Our results provide basic information for use in mitigating nitrate leaching by enhancing microbial denitrification in deep vadose zones in intensive agricultural areas.

中文翻译：

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长期氮肥改变了深层渗流带的微生物群落结构和反硝化能力

目的

在集约化农业中过量使用氮肥增加了硝酸盐向地下水中的淋失，但其对深层渗流区氮素转化过程及相关微生物群落的影响尚不清楚。

材料和方法

从20年的田间试验中收集了0-1050 cm深度的土壤样品，并进行了两种氮肥处理：0（N0）和600 kg N ha ^-1 year ^-1（N600）。进行了扩增子测序和定量PCR分析，以分析土壤微生物群落和反硝化基因的垂直分布。

结果与讨论

土壤深度和氮肥对土壤微生物群落结构和多样性影响很大。250 cm深度被确定为阈值深度，因为在该深度以下和之上都发现了截然不同的微生物群落。定量PCR结果表明，反硝化基因的绝对丰度随着土壤深度的增加而降低。

结论

这项研究阐明了长期氮输入对深层渗流区微生物群落组成和多样性以及反硝化剂的丰富性的深远影响。我们的研究结果为加强集约化农业地区深层渗流带中微生物的反硝化作用提供了基础信息，可用于缓解硝酸盐的淋失。