Responses of nitrification and associated microbial communities to lime and/or ammonium sulfate addition in two acidic soils

Here, we carried out a 45 day microcosm experiment to explore the interactions of lime (Lime) and ammonium sulfate (AS) amendment on net nitrification rate (NNR), ammonia-oxidizers (ammonia-oxidizing archaea (AOA) and bacteria (AOB), completing ammonia-oxidizing bacteria (Comammox)), nitrite-oxidizing bacteria (NOB), and bacterial communities in two acid soils with distinct land-use types (tea plantation soil vs vegetable soil). Lime treatment did not had immediate effect on NNR of both soils on day 7, while significantly increased it on day 45. AS amendment suppressed NNR in the tea plantation soil, but increased it in the vegetable soil, and this stimulation was enlarged with lime addition. AS treatment increased AOA abundance on day 7 in the tea plantation soil, but reduced it in the vegetable soil. However, Lime + AS treatment reduced it in the tea plantation soil, but increased it on day 45 in the vegetable soil. AS treatment decreased AOB and Comammox abundances in the tea plantation soil, while stimulated them in the vegetable soil. AS treatment only increased Nitrobacter and Nitrospira abundances on day 7 in the tea plantation soil, while had no effect on them on day 45 in both soils. Lime enhanced Nitrobacter abundance, but had minor impact on Nitrospira abundance in the tea plantation soil, while remarkably enhanced their abundances on day 45 in the vegetable soil. Lime + AS treatment stimulated Nitrobacter and Nitrospira abundances in both soils. Spearman's correlation analysis and random forest model indicated that AOB, Comammox, and Nitrobacter abundances were positively correlated with NO3--N and NNR in the tea plantation soil, whereas AOA, AOB, Comammox, Nitrobacter and Nitrospira abundances were positively correlated with them in the vegetable soil. Moreover, Lime, AS, and Lime + AS treatments substantially decreased bacterial Chao 1 and Shannon indexes in the tea plantation soil, but Lime and Lime + AS treatments increased them in the vegetable soil. Besides, lime and/or AS amendment shaped bacterial community structure, with major taxa at phyla level and functional groups related to nutrient cycling showing distinct response to different treatments in both soils. These results suggest that AOB, Comammox, and Nitrobacter play crucial roles in lime-increased nitrification of the tea plantation soil amended with or without AS, while AOA, AOB, Comammox, Nitrobacter and Nitrospira contributed mainly to it in the vegetable soil.