Differential adaptability of active ammonia-oxidizing bacteria and archaea to nitrogen amendment and fusarium in monocropped banana soils

This study examines how intensive agricultural management influences ammonia-oxidizing microbial communities (AOB and AOA) in banana monoculture systems, with implications for nitrogen cycling and soil acidification dynamics. While previous research has documented the impact of synthetic fertilizers and pathogens on microbial populations in agroecosystems, the responses of active AOB/AOA taxa under combined nitrogen and disease stressors remain largely uncharacterized. We employed soil microcosms established from a native forest (Y0), a two-year-old (Y2), and a twelve-year-old (Y12) banana plantation. Treatments included urea amendment, Fusarium oxysporum f. sp. cubense (Foc) inoculation, and their combination. AOB/AOA activity was quantified via ¹³CO₂ DNA stable isotope probing, while community composition was analyzed through high-throughput 16 S rRNA gene sequencing. Our results revealed distinct microbial community patterns across land-use types and treatments. AOB dominated in banana plantation soils, with their abundance significantly increasing (p < 0.05) in the Y12 system compared to Y0. Conversely, AOA were predominant in the forest soil. Urea amendment and Foc co-application synergistically enhanced AOB activity in banana soils, withariant community shifts observed across all microcosms. Specifically, urea addition in Y0 soil promoted Nitrosotaleales 1.1-AOA (20.16%) and Nitrosospira cluster 2AOB (88.23%), whereas co-treatment induced a dominance shift to Nitrosospira cluster 3a (72.12%). In Y2 soils, urea alone supported Nitrosospira cluster 2-AOB (84.53%) and Nitrososphaerales Group 1.1b-AOA (72.4%), while combined amendments further increased Nitrosospira cluster 3a-AOB abundance compared to urea-only treatment. These findings establish that AOB play a critical functional role in nitrogen transformation under intensive cropping systems, with their activity patterns strongly influenced by both fertilization and pathogen stressors.