Nitrification is a fundamental process in terrestrial nitrogen cycling. However, detailed information on how climate change affects the structure of nitrifier communities is lacking, specifically from experiments in which multiple climate change factors are manipulated simultaneously. Consequently, our ability to predict how soil nitrogen (N) cycling will change in a future climate is limited. We conducted a field experiment in a managed grassland and simultaneously tested the effects of elevated atmospheric CO₂, temperature, and drought on the abundance of active ammonia-oxidizing bacteria (AOB) and archaea (AOA), comammox (CMX) Nitrospira, and nitrite-oxidizing bacteria (NOB), and on gross mineralization and nitrification rates. We found that N transformation processes, as well as gene and transcript abundances, and nitrifier community composition were remarkably resistant to individual and interactive effects of elevated CO₂ and temperature. During drought however, process rates were increased or at least maintained. At the same time, the abundance of active AOB increased probably due to higher NH₄⁺ availability. Both, AOA and comammox Nitrospira decreased in response to drought and the active community composition of AOA and NOB was also significantly affected. In summary, our findings suggest that warming and elevated CO₂ have only minor effects on nitrifier communities and soil biogeochemical variables in managed grasslands, whereas drought favors AOB and increases nitrification rates. This highlights the overriding importance of drought as a global change driver impacting on soil microbial community structure and its consequences for N cycling.

硝化是陆地氮循环的基本过程。然而，缺乏关于气候变化如何影响硝化菌群落结构的详细信息，特别是来自同时操纵多个气候变化因素的实验的信息。因此，我们预测土壤氮 (N) 循环在未来气候中将如何变化的能力是有限的。我们在管理草地上进行了现场实验，同时测试了大气中 CO ₂升高、温度和干旱对活性氨氧化细菌 (AOB) 和古细菌 (AOA)、comammox (CMX) Nitrospira和亚硝酸盐丰度的影响-氧化细菌（NOB），以及总矿化和硝化速率。我们发现氮转化过程、基因和转录本丰度以及硝化菌群落组成对 CO 2 升高和温度升高的个体和交互影响具有显着的_抵抗力。然而，在干旱期间，加工率增加或至少保持不变。同时，活性 AOB 的丰度增加可能是由于 NH ₄ ⁺可用性较高。AOA 和comammox Nitrospira均因干旱而减少，AOA 和NOB 的活性群落组成也受到显着影响。总之，我们的研究结果表明，变暖和CO ₂升高对管理草地的硝化菌群落和土壤生物地球化学变量影响较小，而干旱则有利于AOB并提高硝化率。这凸显了干旱作为影响土壤微生物群落结构及其对氮循环影响的全球变化驱动因素的压倒性重要性。