Millimeter-scale interactions of nitrogen and potassium on denitrification, anammox, and Feammox in soil fertilization zones

Abstract

Soil denitrification, anammox, and Feammox are key for nitrogen (N) removal in agriculture. Despite potassium (K) fertilizer enhancing N efficiency, their role in regulation of these processes is unclear. A soil column incubation with ¹⁵N isotope tracing was conducted to explore millimeter-scale interactions of N and K on these pathways in soil fertilization zones. After 28 days, individual applications of N and K reduced denitrification-nitrogen removal rate (DNRR), anammox-nitrogen removal rate (ANRR), and feammox-nitrogen removal rate (FNRR) compared to a non-fertilizer control. N fertilizer had a greater effect than K, likely due to the high consumption of dissolved organic carbon by N fertilizer or the increased soil organic matter decomposition by K fertilizer. Combing of N and K increased DNRR, ANRR and FNRR rates by 31 %, 3090 % and 244 % compared to single N, and by and by -53.7 %, 885 % and 222 % compared to single K. These effects diminished with depth and distance from fertilizer sites. The effects of N fertilizer on theses N removal process might be regulate abundance of key microbes (e.g., Limnobacter and Clostridium) and key gene (nirK, hzsB, ACM and Geo) by providing N substrates, while K enhances N metabolism efficiency through enzyme activation, indicated by the downregulation of certain genes (hzsB, ACM and Geo) and a negative correlation with N removal by simultaneously increasing gene expression and enzyme activity. These findings provide insights how N and K together enhance N removal, emphasizing their importance for optimizing this process.