Investigating drivers of N2 loss and N2O reducers in paddy soils across China

Abstract

Denitrification plays a pivotal role in nitrogen (N) cycling in rice paddies, significantly impacting N loss and greenhouse gas emissions. Accurate quantification of net N₂ emissions from paddy fields is therefore essential for improving fertilizer N use efficiency. However, challenges in directly measuring gaseous N₂ hinder our understanding of microbially-mediated N loss in paddy soils at large scales. In this study, we investigated net N₂ loss and its influencing factors in 45 paddy soils across China using membrane inlet mass spectrometry and N₂/Ar technique, complemented by microbial community analysis via metagenomics. Potential N₂ loss rates varied from 0.41 to 3.58 nmol N g⁻¹ h⁻¹, with no significant regional differences. However, soils from rice-upland rotation (1.72 ± 0.64 nmol N g⁻¹ h⁻¹) and mono-rice cropping systems (1.41 ± 0.53 nmol N g⁻¹ h⁻¹) exhibited higher N₂ loss rates compared to double-rice cropping soils (1.13 ± 0.62 nmol N g⁻¹ h⁻¹). Our results revealed a unimodal relationship between soil N₂ loss rates and soil pH, with N₂O reducers and soil properties primarily regulating regional variations in N₂ loss. Significant ecological differentiation was observed within both nosZ Clade I and Clade II, with soil pH emerging as the key factor shaping their community composition. Specifically, in rice-upland rotations, soil moisture and pH significantly influenced nosZ Clade I, while in double-rice cropping systems, soil texture and pH were the main factors affecting nosZ Clade II, thereby driving N₂ loss. These findings enhance our understanding of N₂ loss dynamics in paddy soil ecosystems, underscoring the critical role of N₂O reducers on microbial-derived N₂ loss and highlighting the importance of developing strategies to mitigate N₂O emissions by balancing N₂ loss through the manipulation of N₂O-reducing and N₂O-producing microbes.