Two newly-identified biological nitrification inhibitors in Suaeda salsa: Synthetic pathways and influencing mechanisms

• Oxalic acid (OA) and protocatechuic aldehyde (PA) can inhibit nitrification. • Synthetic pathways of OA and PA were constructed and some key genes were selected. • Inhibition mechanism of OA and PA on Nitrosomonas europaea was revealed. • Inhibitory effect of PA and OA on different agricultural soils was explored. Our research aimed at finding potential BNI resources and exploring the action mechanisms by multiomics. Here, we presented that the Suaeda salsa leaf extracts of both red and green phenotypes from the Yellow River Delta of China showed strong nitrification inhibition ability and selected oxalic acid (OA, molecular weight: 90) and protocatechuic aldehyde (PA, molecular weight: 138) as novel BNIs, then constructed the synthetic pathways and selected some key genes that may influence the synthesis of these two BNIs; and the inhibition mechanisms of these two BNIs on Nitrosomonas europaea were also revealed by performing transcriptomics and metabolomics; and we also found that PA had a nitrification inhibition effect among saline-alkali soil, cinnamon soil and red soil, and the inhibition effect in saline-alkali soil was the most effective, while OA only showed nitrification inhibition effect in red soil. Our findings pointed out a novel plant species as potential BNI resource, and provided opportunities for the design of novel fertilizers, which could improve the crop N utilization efficiency and reduce N loss in agricultural systems.