Environmental factors militating against the activities of ammonia oxidizing archaea and ammonia oxidizing bacteria in soil

This review aims to scrutinize the effect of ammonia concentration, temperature, pH, drought and inhibitors on activity of AOA and AOB in soil. Ammonia concentration in soil increases during drought due to the reduced soil water content and, with desiccation stress or a combination of both factors result in greater inhibition of AOA than AOB during drought. AOA were more susceptible to increased desiccation stress than AOB, irrespective of initial soil ammonium concentration and AOA cultures were more sensitive than AOB to osmotic stress which represent an additional niche differentiating factor between AOA and AOB in soil. Activity and growth of AOA and AOB observed in soil amended with high ammonium concentration at different temperature, suggesting that AOA can contribute to nitrification in highly fertilized soil. The selective inhibition of AOA by simvastatin in culture and in soil provides evidence for oxidation of ammonia by AOB at low ammonium concentration. The findings advance our understanding of the influence of ammonium supply, temperature and osmotic stress on soil nitrification and its role in controlling the availability of ammonium-based fertilizers for plant uptake.