Functional players involved in the distinct nitrogen metabolism in two geographically different paddy soils

Black paddy soil (BP) and gleyed paddy soil (GP) are typical rice-planting soils distributed in two different climatic zones in China. The nitrogen utilization efficiency (NUE) of rice growing on the BP was higher than that in GP even when the soils were transplanted to the same location and subjected to the same agricultural management. In this study, we aimed to explore the microbial mechanisms underlying the difference in nitrogen transformation between the two types of soils. The microcosm experiments using BP and GP were performed under different aeration and temperature conditions with controlled ammonium or nitrate. The results indicated that the nitrification of GP was stronger than that of BP, which was associated with the higher relative abundance of ammonium-oxidizing genes in GP than in BP and a group of specialized ammonium-oxidizing species in GP. It indicated that GP had more vigorous nitrifiers, which is not conducive to the nitrogen utilization of ammonium-preferring rice due to faster ammonium consumption. Moreover, more nitrate was consumed in BP than in GP owing to the higher relative abundance of narG and carbon fixation gene accA in BP. Simultaneously, the overall N₂O accumulation in BP was obviously higher than that in GP, which was associated with higher relative abundance of narG, nirK, and norB and the lower relative abundance of nosZ, as well as some specific norB species enriched in BP. These findings advance our understanding of the microbial mechanism of distinct nitrogen metabolism driving the different NUEs in two types of paddy soils.