The impact of human-induced nitrogen (N) enrichment on microbial diversity has been extensively studied, with two main hypotheses proposed: soil N availability and soil acidification. However, the specific roles of these two hypotheses and their environmental preferences on soil bacterial and fungal communities are not fully understood. By conducting two independent experiments (a 16-year N and a 6-year acid addition) in a temperate semi-arid grassland, we tested the responses of soil microbial attributes (e.g., richness and relative abundance) at various levels (community, phylum/class, and phylotype) to N and acid addition. At the community level, our results showed that both N and acid addition had a negative effect on the richness of the whole, dominant, and rare bacterial communities; N enrichment only decreased the richness of the dominant fungal community, while acid addition decreased the richness of the whole, dominant, and rare fungal communities. By categorizing the microbial attributes into nine environmental preferences based on their responses to N and acid addition, we found that most bacterial phyla were associated with low N availability and high pH preferences, while most fungal classes had other environmental preferences. Most dominant bacterial phylotypes were linked to low N availability and high pH preferences, while most dominant fungal phylotypes were associated with other environmental preferences and high pH preferences. Conversely, most rare bacterial and fungal phylotypes were linked to other environmental preferences. Our experiments revealed that the decline in bacterial richness caused by N enrichment was predominantly due to their sensitivity to soil acidification, while fungal richness remained largely unaltered. By pinpointing distinct microbial attributes at different levels in response to N and acid addition, our findings could potentially forecast how soil microorganisms will react to future global N deposition.

中文翻译：

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土壤微生物属性对长期氮和酸添加的环境偏好：从系统发育型到群落


人类引起的氮（N）富集对微生物多样性的影响已被广泛研究，提出了两个主要假设：土壤氮有效性和土壤酸化。然而，这两种假设的具体作用及其对土壤细菌和真菌群落的环境偏好尚不完全清楚。通过在温带半干旱草原上进行两次独立实验（16年施氮和6年施酸），我们测试了土壤微生物属性（例如丰富度和相对丰度）在不同层面（群落、门）的响应。 /类和系统型）到N和酸的添加。在群落水平上，我们的结果表明，氮和酸的添加对整个、优势和稀有细菌群落的丰富度产生负面影响；氮富集仅降低了优势真菌群落的丰富度，而添加酸则降低了整个、优势和稀有真菌群落的丰富度。通过根据微生物对氮和酸添加的反应将微生物属性分为九种环境偏好，我们发现大多数细菌门与低氮可用性和高pH偏好相关，而大多数真菌类具有其他环境偏好。大多数主要细菌系统发育型与低氮利用率和高 pH 偏好相关，而大多数主要真菌系统发育型与其他环境偏好和高 pH 偏好相关。相反，大多数罕见的细菌和真菌系统型与其他环境偏好相关。我们的实验表明，氮富集引起的细菌丰富度下降主要是由于它们对土壤酸化的敏感性，而真菌丰富度基本保持不变。 通过精确定位不同水平的微生物对氮和酸添加的响应，我们的研究结果有可能预测土壤微生物对未来全球氮沉降的反应。