Tannins originating from root exudates and plant extracts may act as biological nitrification inhibitors (BNIs) for mitigating nitrous oxide (N 2 O) emissions in the context of circular agriculture. However, the differences of condensed (CT) and hydrolysable (HT) tannins in their effects on soil N 2 O emissions remain unclear. This study used incubation and pot experiments combined with structural equation modeling (SEM) to evaluate the comprehensive impacts of the proanthocyanidin (PC) and tannic acid (TA) on soil N 2 O emissions, considering the influence of fertilizer type (urea vs cattle slurry) and plant (absence vs presence). In contrast to the consistent inhibitory effect of 3,4-dimethylpyrazole phosphate (DMPP) applied to both urea- and slurry-amended soils, PC and TA strongly reduced N 2 O emissions from slurry-amended soil, but had differed impact on N 2 O (mitigation by PC and enhancement by TA) for urea-amended soil. More importantly, in the presence of cabbage plants, both PC and TA significantly inhibited N 2 O emissions under both urea and slurry applications, and improved the biomass production and nitrogen use efficiency to different extents. From a microbial perspective, PC and TA likely reduce N 2 O emissions in urea-amended soil by lowering the ( nirS + nirK )/( nosZ I + nosZ II) ratio. In slurry-amended soil, however, they achieve N 2 O mitigation primarily by increasing the abundance of nosZ II while reducing the abundances of AOA , AOB , nirS , and nirK . In conclusion, the impact of PC and TA on soil N 2 O emissions can be fertilizer-specific, however in presence of cabbage plants both PC and TA can mitigate N 2 O emissions regardless fertilizer types. In future it warrants more research to examine the effectiveness of PC and TA on N 2 O mitigation for different cropping systems under various environmental conditions. • Integrated impact of fertilizer type, biological inhibitors and plant on N 2 O were investigated. • N 2 O for urea and slurry application follow an NH 4 + - and NO 3 – -dependent pathway, respectively. • PC and TA from plant sources show potential as effective BNIs to mitigate N 2 O emissions. • PC and TA have a more pronounced inhibitory effect on N 2 O mitigation under slurry fertilization.
Liao et al. (Wed,) studied this question.