Abstract：
Nutrient losses from agricultural ecosystems are increasingly threatening global environmental and human health. Although arbuscular mycorrhizal (AM) fungi have the potential to regulate soil nitrogen (N) loss by enhancing plant uptake and soil particle immobilization, the microbial mechanism behind such mycorrhizal effect is unknown. Herein, by conducting a simulated erosion experiment, we compared the effects of exogenous AM fungal inoculation (Funneliformis mosseae) on the gene abundances and enzyme activities of N-cycling processes, and associated such effect to N uptake and loss. The experiment was composed of combinations of two AM fungal treatments (control vs. AM fungal inoculation), two crops (maize vs. soybean) and two slopes of the plots (6° vs. 20°). The experimental plots subjected to natural rainfalls to simulate the erosion events. We showed that the effects of AM fungi were greater in the maize soils than in the soybean soils. In the maize soils, AM fungi increased the abundances of N-fixing (+81.1 %) and nitrifying genes (+200.7 %) and N cycling enzyme activity (+22.3 %). In the soybean soils, AM fungi increased the N-fixing gene abundance (+36.9 %) but decreased the abundance of nitrifying genes (-18.9 %). The abundance of N-fixing gene was positively correlated with N uptake but negatively correlated with N loss. Additionally, AM fungi enhanced the effects of mycorrhizal colonization and moisture but decreased the effects of nutrients on soil microbial metrics related to N-cycling processes. Therefore, AM fungal inoculation enhanced N uptake and reduced N loss by increasing N-fixing gene abundance, and that AM fungi should be preferably used for the low N environments or for the ecosystems highly limited by or competing for N.
摘要：
农业生态系统的养分流失正日益威胁着全球环境和人类健康。尽管丛枝菌根（AM）真菌具有通过增强植物吸收和土壤颗粒固定来调节土壤氮（N）损失的潜力，这种菌根效应背后的微生物机制是未知的。在这里，通过进行模拟侵蚀实验，我们比较了外源AM真菌接种（真菌）对N循环过程的基因丰度和酶活性的影响，并将这种效应与氮的吸收和损失相关联。实验由两种AM真菌处理的组合组成(对照与AM真菌接种)，两种作物(玉米与大豆)和地块的两个斜坡(6°与20°)。实验地块经受自然降雨来模拟侵蚀事件。我们表明，玉米土壤中AM真菌的影响大于大豆土壤中AM真菌的影响。在玉米土壤中，AM真菌增加了固氮（81.1％）和硝化基因（200.7％）和氮循环酶活性（22.3％）的丰度。在大豆土壤中，AM真菌增加了N固定基因的丰度（36.9％），但降低了硝化基因的丰度（-18.9％）。N固定基因的丰度与N吸收呈正相关，而与N损失呈负相关。此外,AM真菌增强了菌根定植和水分的影响，但降低了养分对与氮循环过程相关的土壤微生物指标的影响。因此,AM真菌接种通过增加N固定基因丰度来增强N吸收并减少N损失，并且AM真菌应优选用于低氮环境或高度受N限制或竞争N的生态系统
