Long-term nitrogen fertilization alters microbial community structure and denitrifier abundance in the deep vadose zone

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.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.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.

本研究从一项为期20年的田间定位试验中采集了0~1050厘米深度的土壤样品，该试验设置两种氮肥施用处理：施氮量为0 kg N ha⁻¹·a⁻¹（记为N0）与600 kg N ha⁻¹·a⁻¹（记为N600）。采用扩增子测序（Amplicon sequencing）与定量PCR（quantitative PCR）分析手段，解析了土壤微生物群落与反硝化基因（denitrification genes）的垂直分布特征。土壤微生物群落结构与多样性显著受土壤深度与氮肥施用的调控。研究确定250厘米为临界深度，该深度上下方的土壤微生物群落结构存在显著差异。定量PCR结果显示，反硝化基因的绝对丰度随土壤深度增加而逐渐降低。本研究阐明了长期氮素输入对深层包气带（deep vadose zone）微生物群落组成与多样性，以及反硝化微生物丰度的深远影响。本研究结果可为集约化农业区通过强化深层包气带中的微生物反硝化作用以缓解硝酸盐淋失提供基础参考依据。