Although nitrogen (N) enrichment enhances both soil N availability and soil acidification, it is difficult to isolate their effects on microbial taxa that drive the soil carbon (C) dynamics under different microbial C limitation conditions in natural ecosystems. Based on long-term field N addition, field acid addition, and laboratory incubation experiments in the Inner Mongolian grassland, we disentangled the effects of increased N availability and soil acidification on relative abundance of bacterial and fungal taxa under the mild (soil incubation for 28 days) and strong microbial C limitations (soil incubation for 191 days). Bacterial and fungal taxa are grouped into four ecological categories (N sensitive, acid sensitive, N and acid sensitive, N and acid insensitive) with multiple levels of N addition. In the context of the mild microbial C limitation, increased N availability promoted the relative abundance of the fungal class Eurotiomycetes (N positive sensitivity) under the low–medium levels of N addition, with an associated decrease in soil labile carbonyl C content. Conversely, increased N availability reduced the relative abundance of fungal class Sordariomycetes (N negative sensitivity) and bacterial gene copies (N and acid negative sensitivity) under the high levels of N addition, with associated increases in labile O-alkyl C and di-O-alkyl C content, making soil C more labile. In the context of the strong microbial C limitation, increased soil acidification promoted the abundance of acidophilous fungal classes Sordariomycetes and Eurotiomycetes under the low–medium levels of N addition, with an associated decrease in soil labile carbonyl C content. However, increased N availability promoted the relative abundance of the bacterial phylum Thaumarchaeota (N positive sensitivity equal to acid negative sensitivity), with associated low labile O-alkyl C and di-O-alkyl C content, leaving C chemistry more resistant. By applying the ecological category concept to soil microbes, our findings highlight that the N enrichment-induced shifts in abundance of N- and/or acid-sensitive categories are tightly associated with the changes in soil organic carbon (SOC) chemical composition, and the relationship between microbial function groups and SOC chemistry varied substantially under the mild versus strong microbial C limitations.

尽管氮 (N) 富集增强了土壤 N 可用性和土壤酸化，但很难分离它们对在自然生态系统中不同微生物 C 限制条件下驱动土壤碳 (C) 动态的微生物分类群的影响。基于在内蒙古草原的长期田间施氮、田间酸添加和实验室孵化实验，我们分离了在温和条件下（土壤孵化 28天）和强烈的微生物 C 限制（土壤孵化 191 天）。细菌和真菌类群分为四个生态类别（N敏感、酸敏感、N和酸敏感、N 和酸不敏感) 具有多个 N 添加水平。在温和的微生物 C 限制的背景下，增加的 N 可用性促进了在低-中等 N 添加水平下真菌类 Eurotiomycetes（N 阳性敏感性）的相对丰度，伴随着土壤不稳定羰基 C 含量的降低。相反，增加的 N 可用性降低了真菌类 Sordariomycetes（N 负敏感性）和细菌基因拷贝（N 和酸负敏感性）的相对丰度) 在高水平的 N 添加下，伴随着不稳定的 O-烷基 C 和二-O-烷基 C 含量的增加，使土壤 C 更不稳定。在强微生物 C 限制的背景下，增加的土壤酸化促进了嗜酸真菌类 Sordariomycetes 和 Eurotiomycetes 在中低氮添加量下的丰度，伴随着土壤不稳定羰基 C 含量的降低。然而，增加的 N 可用性促进了细菌门 Thaumarchaeota 的相对丰度（N 正敏感性等于酸负敏感性)，具有相关的低不稳定 O-烷基 C 和二-O-烷基 C 含量，使 C 化学更具抵抗力。通过将生态类别概念应用于土壤微生物，我们的研究结果强调，N 富集引起的 N 和/或酸敏感类别丰度的变化与土壤有机碳 (SOC) 化学成分的变化密切相关，并且微生物功能组和 SOC 化学之间的关系在轻度和强微生物 C 限制下有很大差异。