Differential impacts of lime and nitrogen amendment on nitrification, ammonia oxidizers, nitrite oxidizers, and bacterial communities in two acidic soils

Nitrification plays a vital role in shaping nitrogen (N) availability and soil acidification. However, effects of lime and N fertilizer amendment on nitrification and microbial communities in acidic soils remain poorly understood. Here, we carried out a short-term microcosm experiment on two acidic soils with distinct land-use types (tea plantation versus vegetable cultivation) to study the impacts of lime and/or ammonium sulfate (NH₄⁺) on net nitrification rates (NNR), the abundances of ammonia-oxidizing archaea (AOA) and bacteria (AOB), complete ammonia-oxidizing bacteria (Comammox), and nitrite-oxidizing bacteria (NOB), and bacterial communities. We observed that lime-only did not immediately impact NNR in both soils in the beginning of incubation period, but it increased significantly towards the end of the experiment, and combining lime with NH₄⁺ enhanced this effect. Particularly, the NH₄⁺-only increased NNR in vegetable soil, but decreased it in tea plantation soil. In vegetable soil, the abundance of AOB, Comammox, Nitrobacter-like NOB, and Nitrospira-like NOB increased to a greater extent under lime + NH₄⁺ treatment relative to the NH₄⁺ treatment after a 45-day incubation. However, this pattern was only observed for Comammox and Nitrobacter-like NOB in tea plantation soil. AOB, Comammox, and Nitrobacter-like NOB were correlated with NNR in tea plantation soil, while all nitrifiers jointly shaped it in vegetable soil. In addition, lime and/or NH₄⁺ substantially decreased bacterial α-diversity in tea plantation soil, while only lime with or without NH₄⁺ increased it in vegetable soil. Both lime and/or NH₄⁺ altered bacterial community structure at the phylum level. Overall, above findings highlight the ecological importance of lime- and ammonium-induced impacts on soil N cycling and microbial communities across different types of acidic soils.