Nitrogen (N) deposition is projected to increase over the coming decades, with consequences on soil N transformation. Soil N mineralization is an important process regulating soil N availability. However, it is unclear how the responses of soil N mineralization to increasing N deposition are controlled by biotic and abiotic factors. Here, we examined the effects of increasing N addition rates on soil net N mineralization, net nitrification, and N-cycling functional gene abundance in a temperate meadow steppe after six years treatments. We found that N addition significantly increased the rates of soil net N mineralization and nitrification. Nitrogen addition rates were positively correlated with the abundance of ammonia-oxidizing bacteria amoA gene, but negatively correlated with that of other N-related functional genes. The N-induced enhancement of net N transformations were predominantly driven by the enhanced quantity and quality of soil substrates, but not by N-related functional genes. Decreased soil pH also contributed to the enhancement of net N transformations. Our findings highlight the importance of soil substrate availability and soil pH in driving grassland soil N transformation processes under the scenario of increasing N deposition.

预计未来几十年氮 (N) 沉积量将增加，对土壤 N 转化产生影响。土壤氮矿化是调控土壤氮素有效性的重要过程。然而，目前尚不清楚土壤氮矿化对氮沉积增加的响应是如何受生物和非生物因素控制的。在这里，我们研究了在经过 6 年处理的温带草甸草原中，增加 N 添加率对土壤净 N 矿化、净硝化和 N 循环功能基因丰度的影响。我们发现 N 添加显着增加了土壤净 N 矿化和硝化的速率。除氮率呈正同丰氨氧化菌的相关AMO一个基因，但与其他 N 相关功能基因负相关。N 诱导的净 N 转化增强主要是由土壤基质的数量和质量的增加驱动的，而不是由 N 相关的功能基因驱动的。土壤 pH 值的降低也促进了净氮转化。我们的研究结果强调了在氮沉积增加的情况下土壤基质可用性和土壤 pH 值在驱动草地土壤氮转化过程中的重要性。