Temperature-dependent changes in active nitrifying communities in response to field fertilization legacy

Using DNA-based stable isotope probing (SIP) in microcosms, we demonstrate the shifts in active nitrifying communities in soil from field plots imposed by 8 years of mineral fertilizer N (NPK) or manure (M) applications compared with an unfertilized control (CK), and associated shifts in their temperature sensitivity. DNA-SIP indicates that ammonia-oxidizing archaea (AOA) were labeled to a much greater extent in the CK soil (74.6%) than in the NPK-amended (19.8%) or M-amended (27.1%) soils at 28 °C. In contrast, NPK soil showed the highest labeling of ammonia-oxidizing bacteria (AOB) (23.3%) relative to M (4.03%) and CK (2.42%) soils. This is further supported by significant decreases in the ¹³C-amoA gene ratios of AOA/AOB in the NPK (4.14) and M (8.63) compared with CK (46.4) soils at 28 °C, while little difference was observed at 35 °C. The relative abundance of active AOA or AOB in the manure was between that in the CK and NPK soils. This may be attributable to the slower release of ammonium mineralized from manure than from urea. The active AOA in soil microcosms were dominated by Nitrososphaera viennensis-like groups regardless of fertilization history or temperature. Nitrosomonas communis-like AOB may be more adapted to the higher temperature than Nitrosospira cluster 3-like AOB. The labeling of nitrite oxidizers (nitrite-oxidizing bacteria) was lowest in NPK soil and was higher at 28 °C than 35 °C regardless of fertilization treatment. The finding indicates that intensified anthropogenic N inputs in the field may select for distinct active nitrifying communities that exhibited different temperature sensitivities.