Effect of different fertilization regimes on the vertical distribution of anaerobic ammonium oxidation in paddy soils

Abstract

Fertilization is a necessary practice for paddy fields to achieve high crop yields, and this practice could have an important impact on soil nitrogen cycle. Anammox (anaerobic ammonium oxidation) is an important process in the nitrogen cycle of paddy ecosystems. However, until now, the influence of nitrogen fertilization on anammox, is not well understood. Here, the vertical distribution of the activity, abundance and community composition of anammox bacteria was investigated in paddy soils (0–50 cm) under three different fertilizer treatments: chemical fertilizer (CF), organic fertilizer (OF) and unfertilized control (CK). The 15N tracer experiments confirmed anammox activity in different depths of paddy soils across all treatments, with the highest activity in the surface soil layer (0–10 cm) under OF treatment. The potential anammox rates were 0.76–1.82, 0.95–2.39 and 1.19–3.62 nmol N g−1 (dry soil) h−1, respectively, under CK, CF and OF treatments. The abundance of anammox bacterial hzsA genes in upper 30 cm layers was significantly higher under CF (3.1 × 106-6.5 × 106 copies g−1 dry soil) and OF (3.4 × 106-7.1 × 106 copies g−1 dry soil) treatments than CK treatment (2.1 × 106-3.5 × 106 copies g−1 dry soil). Similar community composition of anammox bacteria was observed in soils under different fertilizer treatments, with Candidatus Brocadia being the single dominant genus. Overall, our results demonstrated that the input of inorganic or organic fertilizers significantly increased the anammox bacterial abundance and activity in both surface and subsurface paddy soils, while the anammox community remained relatively stable.