Data_Sheet_1_Nitrogen fertilization promoted microbial growth and N2O emissions by increasing the abundance of nirS and nosZ denitrifiers in semiarid maize field.docx

Nitrous oxide (N2O) emissions are a major source of gaseous nitrogen loss, causing environmental pollution. The low organic content in the Loess Plateau region, coupled with the high fertilizer demand of maize, further exacerbates these N losses. N fertilizers play a primary role in N2O emissions by influencing soil denitrifying bacteria, however, the underlying microbial mechanisms that contribute to N2O emissions have not been fully explored. Therefore, the research aimed to gain insights into the intricate relationships between N fertilization, soil denitrification, N2O emissions, potential denitrification activity (PDA), and maize nitrogen use efficiency (NUE) in semi-arid regions. Four nitrogen (N) fertilizer rates, namely N0, N1, N2, and N3 (representing 0, 100, 200, and 300 kg ha−1 yr.−1, respectively) were applied to maize field. The cumulative N2O emissions were 32 and 33% higher under N2 and 37 and 39% higher under N3 in the 2020 and 2021, respectively, than the N0 treatment. N fertilization rates impacted the abundance, composition, and network of soil denitrifying communities (nirS and nosZ) in the bulk and rhizosphere soil. Additionally, within the nirS community, the genera Cupriavidus and Rhodanobacter were associated with N2O emissions. Conversely, in the nosZ denitrifier, the genera Azospirillum, Mesorhizobium, and Microvirga in the bulk and rhizosphere soil reduced N2O emissions. Further analysis using both random forest and structural equation model (SEM) revealed that specific soil properties (pH, NO3−-N, SOC, SWC, and DON), and the presence of nirS-harboring denitrification, were positively associated with PDA activities, respectively, and exhibited a significant association to N2O emissions and PDA activities but expressed a negative effect on maize NUE. However, nosZ-harboring denitrification showed an opposite trend, suggesting different effects on these variables. Our findings suggest that N fertilization promoted microbial growth and N2O emissions by increasing the abundance of nirS and nosZ denitrifiers and altering the composition of their communities. This study provides new insights into the relationships among soil microbiome, maize productivity, NUE, and soil N2O emissions in semi-arid regions.

氧化亚氮（N₂O）排放是气态氮流失的主要来源，会引发环境污染。黄土高原地区土壤有机质含量偏低，加之玉米对肥料的需求量大，进一步加剧了氮素流失。氮肥通过影响土壤反硝化细菌成为N₂O排放的主要驱动因子，但目前学界尚未完全阐明N₂O排放背后的潜在微生物机制。因此，本研究旨在阐明半干旱地区氮肥施用、土壤反硝化作用、N₂O排放、潜在反硝化活性（Potential Denitrification Activity, PDA）与玉米氮肥利用效率（Nitrogen Use Efficiency, NUE）之间的复杂关联。本试验在玉米田设置4个氮肥施用量梯度：N0、N1、N2、N3，分别对应0、100、200、300 kg·ha⁻¹·yr⁻¹。2020年和2021年，N2处理下的累积N₂O排放量分别较N0处理高32%和33%，N3处理则分别较N0处理高37%和39%。氮肥施用量会影响根际土与非根际土中土壤反硝化微生物群落（nirS与nosZ功能型）的丰度、组成及群落网络结构。此外，在nirS型群落中，贪铜菌属（Cupriavidus）和红杆菌属（Rhodanobacter）与N₂O排放存在显著关联。与之相反，在nosZ型反硝化微生物中，根际土与非根际土中的固氮螺菌属（Azospirillum）、中慢生根瘤菌属（Mesorhizobium）和微枝形杆菌属（Microvirga）可降低N₂O排放。进一步通过随机森林与结构方程模型（Structural Equation Model, SEM）分析发现：特定土壤理化性质（pH、硝态氮NO₃⁻-N、土壤有机碳SOC、土壤含水量SWC与可溶性有机氮DON）以及携带nirS基因的反硝化微生物，分别与潜在反硝化活性（PDA）呈正相关；上述因子与N₂O排放及PDA均存在显著关联，但对玉米氮肥利用效率（NUE）产生负向影响。而携带nosZ基因的反硝化微生物则表现出相反的趋势，表明其对上述变量的作用效应存在差异。本研究结果表明，氮肥施用通过提高nirS型与nosZ型反硝化微生物的丰度并改变其群落组成，促进了微生物生长与N₂O排放。本研究为半干旱地区土壤微生物组、玉米生产力、氮肥利用效率与土壤N₂O排放之间的关联提供了新的研究视角。