Plant diversity reshapes drought resistance across soil nitrifier guilds

Drought is a major climate stressor threatening global terrestrial ecosystems. Within the biodiversity–ecosystem function framework, plant diversity is thought to stabilise ecological processes and enhance ecosystem resistance to climate change. However, its role in shaping the drought resistance of soil nitrogen (N) cycling remains unclear. We combined a field survey with a pot experiment (914 soil samples) to examine how distinct nitrifier groups, including ammonia‐oxidising archaea (AOA), ammonia‐oxidising bacteria (AOB) and complete ammonia oxidisers (comammox), respond to drought across plant diversity levels. We found that drought reduced AOB and comammox activity but not AOA activity. Increasing plant richness enhanced AOA resistance, reduced AOB resistance, and had no effect on comammox resistance. Notably, AOA and AOB resistance exhibited contrasting temporal patterns during drought progression, with AOA resistance increasing and AOB resistance declining across successive drought progression stages. In contrast, comammox resistance showed little temporal variation during drought progression and was influenced indirectly by plant diversity through changes in soil NH 4 + availability. Synthesis . These findings suggest that plant diversity reshapes, rather than uniformly enhances, drought resistance across nitrifier guilds in a temporally dynamic and resource‐mediated manner, emphasising the need to incorporate microbial functional types and drought temporal dynamics into predictions of global N cycling under climate change.