Nitrification and ammonia-oxidizing bacteria shift in response to soil moisture and plant litter quality in arid soils from the Patagonian Monte

• We studied the effect of soil moisture and plant litter quality on nitrification.
• We analyzed microcosms constructed with soils from an arid ecosystem.
• Low soil moisture and plant litter quality negatively influenced nitrification.
• amoA genes from AOB increased with both high soil moisture and litter quality.
• Bacterial amoA genes were up to3170 times more abundant than archaeal amoA genes.

We aimed to evaluate the effects of both plant litter quality, characteristic of sites with different histories of grazing disturbance, and soil water content on nitrification in soils from an arid ecosystem of Patagonia. To reach this goal, soil microcosms covered by plant litter of different quality and subjected to different soil water conditions were sampled at different times to analyze: (i) the nitrifying enzyme activity; (ii) the concentration of inorganic forms of nitrogen; and (iii) the abundance of bacterial (AOB) and archaeal (AOA) amoA genes. Soil water enhanced nitrifying activity in average 16% during the period of highest nitrification rates, and nitrate concentration in average 733% after 70 days of incubation. Microcosms amended with high litter quality showed the highest ammonium and the lowest phenolics concentrations, and higher or equal nitrification rates than microcosms amended with poor litter quality. After one week of incubation, the combination of both high litter quality and soil water significantly enhanced amoA gene abundance from AOB (p < 0.05). The AOB:AOA amoA genes ratio ranged from 12 to 3170. Altogether, our results suggest that high soil water and litter quality exerted positive effects over the nitrifying activity and the abundance of AOB but not AOA in these arid soils.