Soil bacterial α and β diversity patterns under nitrogen (N) addition have been intensively examined, but γ diversity patterns remain largely unknown, especially, the mechanisms that concurrently control changes in α, β and γ diversity remain elusive. Therefore, we formulated a conceptual framework that simultaneously considers candidate drivers including ubiquitous species, rare species, and community assembly processes to elucidate the driving mechanisms of α, β and γ diversity under N addition. The conceptual framework was tested by compiling the sequence data of seven studies published from January 1997 to May 2022 and following the same analysis as our own two long-term multilevel N addition experiments. We demonstrate that subtractive heterogenization based on environment selection simultaneously predicts the changes in α, β and γ diversity under long-term N addition. That is, long-term N addition led to the decline of ubiquitous species (subtractive processes) through low soil pH, and promoted the strength of heterogeneous selection (heterogeneous processes) via enhancing environmental heterogeneity, subsequently causing lower α diversity and γ diversity but higher β diversity. These results mean that N addition may lead to a significant loss of soil bacterial diversity around the world. Together, these findings offer a way to simultaneously predict soil bacterial α, β and γ diversity responses to the ongoing atmospheric nitrogen deposition.

中文翻译：

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长期氮添加下土壤细菌α和β多样性的驱动机制：基于环境选择的减法异质化

氮（N）添加下土壤细菌的α和β多样性模式已被深入研究，但γ多样性模式仍然很大程度上未知，特别是同时控制α、β和γ多样性变化的机制仍然难以捉摸。因此，我们制定了一个概念框架，同时考虑了普遍存在的物种、稀有物种和群落组装过程等候选驱动因素，以阐明氮添加下α、β和γ多样性的驱动机制。通过编译 1997 年 1 月至 2022 年 5 月发表的七项研究的序列数据，并遵循与我们自己的两项长期多水平 N 添加实验相同的分析，对概念框架进行了测试。我们证明，基于环境选择的消减异质化同时预测了长期氮添加下α、β和γ多样性的变化。也就是说，长期施氮通过降低土壤pH值导致普遍存在物种的减少（消减过程），并通过增强环境异质性增强异质选择（异质过程）的强度，从而导致α多样性和γ多样性降低，但更高β多样性。这些结果意味着氮的添加可能会导致世界各地土壤细菌多样性的显着丧失。总之，这些发现提供了一种同时预测土壤细菌 α、β 和 γ 多样性对持续大气氮沉降反应的方法。