Nitrogen (N) from anthropogenic sources has dramatically increased in terrestrial ecosystems globally. Although belowground microbial processes and events that release N into the atmosphere, such as fire, could support ecosystem resilience to eutrophication, little is known about how these factors might affect N loss following chronic fertilization, thus promoting ecosystem recovery. We studied how N pools, N-cycling potential rates and their affiliated microbial populations, and microbial community composition responded to the factorial effects of cessation of 30 years of chronic N fertilization and annual burning at a tallgrass prairie. Soil N availability in previously fertilized plots recovered by 86% (using never-fertilized control plots as a 100% recovery reference), while plant and microbial biomass did not change. Nitrification potential recovered (80%), and denitrification potential partially recovered (50%), in previously fertilized plots. There were differential responses among key groups of nitrifiers (archaea vs. bacteria) and denitrifiers (nosZ clade I vs. clade II from Anaeromyxobacter dehalogenans) to long-term N fertilization and cessation despite the whole microbial community composition not shifting significantly after fertilization ceased. Also, N-cycling potentials were consistently higher in unburned prairie. Together, results suggest that fire is a prominent mechanism for ecosystem N removal in annually burned prairie, while N-cycling microbes will have an important role in the absence of fire; however, the recovery to pre-fertilized condition, with or without fire, will take longer than 1 year. Overall, differential resilience of biotic populations and processes can potentially shape different outcomes of soil N loss and tallgrass prairie ecosystem recovery from long-term N fertilization.

在全球陆地生态系统中，来自人为来源的氮（N）急剧增加。尽管地下微生物过程和事件将氮释放到大气中，例如火，可以支持生态系统对富营养化的恢复力，但对于这些因素如何影响长期施肥后氮素的损失并由此促进生态系统的恢复知之甚少。我们研究了氮池，氮循环潜力率及其相关的微生物种群以及微生物群落组成如何响应高草草原上停止长期施氮30年和每年燃烧的因子效应。以前施肥的地块土壤氮素利用率恢复了86％（使用从未施肥的对照地块作为100％回收率参考），而植物和微生物的生物量没有变化。在以前施肥的地块中，硝化作用的潜力得以恢复（80％），部分反硝化作用的潜力得以恢复（50％）。在硝化器（古细菌与细菌）和反硝化器（nosZ进化枝I与从脱氧厌氧杆菌获得的进化枝II ）到长期N的受精和停止，尽管在停止受精后整个微生物群落组成没有明显变化。同样，在未燃烧的草原上，N循环的潜力始终较高。总之，结果表明，火是每年燃烧大草原中去除生态系统氮的重要机制，而在没有火的情况下，氮循环微生物将发挥重要作用。但是，无论是否着火，要恢复到受精前的状态都将花费超过1年的时间。总体而言，生物种群和过程的不同复原力可能会影响长期氮肥施用后土壤氮素损失和草丛草原生态系统恢复的不同结果。