Bacterial and archaealamoAgene distribution covaries with soil nitrification properties across a range of land uses

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Ammonia-oxidizing bacteria and ammonia-oxidizing archaea are commonly found together in soils, yet the factors influencing their relative distribution and activity remain unclear. We examined archaeal and bacterialamoAgene distribution, and used a novel bioassay to assess archaeal and bacterial contributions to nitrification potentials in soils spanning a range of land uses (forest, pasture, cultivated and long-term fallowed cropland) along a 10 km transect. The assay, which quantifies the extent to which acetylene-inactivated soil nitrification potential recovers (RNP) in the presence of bacterial protein synthesis inhibitors, indicated a significant archaeal contribution to the nitrification potentials of the pasture and long-term fallowed soils. ArchaealamoAgene abundance did not vary significantly among the soils, but bacterialamoAgene abundance did, resulting in archaeal : bacterialamoAabundance ratios ranging from 1.1 ± 0.8 in cultivated soils to 396 ± 176 in pasture soils. Both archaeal and bacterialamoAgene compositions were heterogeneous across the landscape, but differed in their patterns of variability. ArchaealamoAgene distributions were distinct among each of the three main land-use types: forest, pasture and cropland soils. In contrast, bacterialamoAgene composition was distinct in forest and in cultivated cropland, while pasture and long-term fallowed cropland soils were similar. In both pasture and long-term fallowed cropland soils, one phylotype ofNitrosospiracluster 3a was highly abundant. This distinct bacterialamoAgene fingerprint correlated with significant contributions of archaea to RNP of both soils, despite differences in archaealamoAgene composition between the pasture and fallowed soils. This observation suggests that the factors driving the development of ammonia-oxidizing bacteria community composition might influence the extent of archaeal contribution to soil nitrification.

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