Abstract
Both bacterial and archaeal ammonia oxidizers (AOB and AOA) are abundant in most soils, but their relative contributions to soil nitrification under different conditions are still debated. This study investigates the influence of long-term zinc (Zn) stress on the ammonia oxidizer community and determines the role of AOB and AOA in Zn tolerant nitrification. This was assessed by artificially spiking a grassland soil with 1300 and 2400 mg Zn kg−1 (final concentration). Both treatments increased Zn tolerance after incubation for 12 months and increased the AOB/AOA amoA gene abundance ratio from 0.1 to 30. Soil samples were subsequently subjected to stable isotope probing (SIP) of DNA by incubation under 13CO2 atmosphere. 13CO2 was assimilated by AOB in the uncontaminated soil. In contrast, this assimilation was not observed for the AOA. Similarly, AOB and not AOA assimilated 13CO2 after Zn exposure for 12 months. These results show that recovery of nitrification and development of Zn tolerance after long-term Zn exposure in this soil is due to the initial activity of AOB, rather than AOA.
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