Distribution Of Aerobic Ammonia Oxidizers And Their Response To The Environments In The Chinese Critical Zone

The critical zone (CZ) is the most heterogeneous near-surface environments where complex interaction happen betweem rock, soil, water, air, and living organisms.The microbes play the foundmental roles in the energy and elements fluxes exchanged between these environments in the CZ. Here we studied two key microbial functional groups in soils, water and hot springs. One group is the ammonia oxidizing microorganisms including bacterial (AOB) and archaeal (AOA) oxidizers that intermediate the first and also the rate-limiting step of nitrification to oxidize ammonia into nitrite.Investigation of AOB and AOA in soils across China (7 provinces) showed that the abundance of AOA amoAgenes thatencodes the alpha subunit of ammonia monooxygenase were higher than AOB amoA genes. Soil locations and soil types were the most important driver sturcturing both AOB and AOA community compositions. Soil physicochemical properties such as pH, contents of TOC, ammonia and water were also important factors determing the AOB and AOA community strctures.Investigation of ammonia oxidizing communities in agricultural soils collectedfrom eastern China (over a 17° latitude gradient)showed that the Nitrosospira and Nitrososphaera were the dominant clusters of AOB and AOA, respectively;but the subc luster-level composition of Nitrosospira-related AOB and Nitrososphaera-related AOA varied across the latitudinalgradient. Variance partitioning analysis showed that geography and climatic conditions (e.g., mean annual temperature and precipitation),as well as carbon-/nitrogen-related soil nutrients, contributed more to the AOB and AOA community variations(～50% in total) than soil pH (～10% in total). Soil type has the most important impacts on the composition of AOB and AOA in paddy soils and cold soils collected from different provinces that undergo different climate condition and soil pysicochemistry.We also investigated water physicochemical gradients and community structures of ammonia oxidizing bacteria (AOB) and archaea (AOA) over 100 km in the Three GorgesReservoir (TGR) from the dam. Water environmental gradients was elongated by the constrcution of the Three Gorges Dam (TGD). the water quality was relatively stable in the upstream reservoir (>50km away from the dam) but significantly deteriorated in the lowersegment0-25km near the dam. The increased environmental gradients had remarkable impacts on the abundance but not the composition of AOB and AOA.Nutrient accumulation favored the growth of AOB but inhibited AOAin the lower segment near the dam and reversed the predominant role of particle-attached fractions to free-living counterparts. Nitrosospira-and Nitrosopumilus-affiliated clusters were dominant particle-attached and free-living AOB and AOA, respectively. Majority of both AOB and AOA were dispersed from upstream mainstream water and kept rather constant along the reservoir. Our results indicated that the environmental gradients formed by construction of the TGD did not change the major compositions of aerobic ammonia oxidizers but did influence the abundance of this functional group.