Abstract Ammonia-oxidizing archaea (AOA) and bacteria (AOB) drive nitrification and therefore critically modulate plant nitrogen (N) utilization, ecosystem N retention and environmental effects of reactive N. Previous studies have shown that abiotic factors (e.g., soil ammonium concentration, pH) can largely control the abundance and composition of ammonia oxidizers. However, whether the biotic factors, such as heterotrophic microbes play a role in impacting AOA and AOB remain unknown. Here, we conducted two experiments to assess the impacts of heterotrophs on AOA and AOB. First, a microcosm experiment was designed to create environments with different competition intensities between heterotrophic microbes and ammonia oxidizers through adding different amounts and ratios of organic C (cellulose) and mineral N [(NH4)2SO4] into two agriculture soils with long-term distinct fertilization histories. Along with the carbon to nitrogen (C/N) ratio gradient, rapid decreases in AOA and AOB abundances occurred accompanied with increased total microbial biomass and activities (respiration), suggesting intense competition between heterotrophic microbes and ammonia oxidizers. Pyrosequencing data revealed that different C/N ratios of substrate had significant impacts on the composition of the AOB but not on AOA communities. Second, to test whether there were inhibitive interactions through metabolic compounds, we examined the effect of water extracts of soils amended with high ratios of cellulose and ammonium sulfate on AOA /AOB abundances. The results showed that the extracts from substrates with C/N ratio of 50 and 100 reduced AOA and AOB abundance significantly, although this negative effect abated over time. Together, our findings indicate that both direct competition and inhibition by microbial metabolites critically affect AOA and AOB communities, providing new insights into the mechanisms that underlie ammonia oxidizer dynamics in agricultural ecosystems.

中文翻译：

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两种农业土壤不同碳氮添加量下氨氧化古菌和细菌对异养生物的响应

摘要 氨氧化古菌 (AOA) 和细菌 (AOB) 驱动硝化作用，因此对植物氮 (N) 的利用、生态系统氮的保留和活性氮的环境影响进行了关键调节。先前的研究表明，非生物因素（例如土壤铵浓度、 pH）可以在很大程度上控制氨氧化剂的丰度和组成。然而，异养微生物等生物因素是否在影响 AOA 和 AOB 方面发挥作用仍然未知。在这里，我们进行了两个实验来评估异养生物对 AOA 和 AOB 的影响。第一的，通过向两种具有长期不同施肥历史的农业土壤中添加不同数量和比例的有机碳（纤维素）和矿物质氮 [(NH4)2SO4]，设计了一个微观实验，以创造异养微生物和氨氧化剂之间具有不同竞争强度的环境. 随着碳氮 (C/N) 比梯度的增加，AOA 和 AOB 丰度迅速下降，同时微生物总生物量和活动（呼吸）增加，表明异养微生物和氨氧化剂之间存在激烈竞争。焦磷酸测序数据显示，底物的不同 C/N 比对 AOB 的组成有显着影响，但对 AOA 群落没有影响。其次，通过代谢化合物测试是否存在抑制性相互作用，我们检查了用高比例纤维素和硫酸铵改良的土壤水提取物对 AOA/AOB 丰度的影响。结果表明，C/N 比为 50 和 100 的底物提取物显着降低了 AOA 和 AOB 丰度，尽管这种负面影响会随着时间的推移而减弱。总之，我们的研究结果表明，微生物代谢物的直接竞争和抑制都会严重影响 AOA 和 AOB 群落，为农业生态系统中氨氧化动力学的基础机制提供了新的见解。