Effect of n-hexadecanoic acid on N2O emissions from vegetable soil and its synergism with Pseudomonas stutzeri NRCB010

Recently, it has been recommended to utilize specific plant root metabolites to decrease nitrous oxide (N2O) emissions from agricultural soil. However, only a limited number of plant root metabolites have been shown to decrease soil N2O emissions, and their combined effects with plant growth-promoting rhizobacteria, as well as the mechanisms involved in mitigating N2O emissions, remain to be explored. This study investigated the impact and microbial mechanisms of three tomato root exudate metabolites, namely, methyl hexadecanoate, methyl stearate, and n-hexadecanoic acid, on N2O emissions. In a pure culture experiment, n-hexadecanoic acid significantly enhanced Pseudomonas stutzeri NRCB010 auxin production, nitrogen removal, N2O reduction capacity, and N2O reductase activity. Methyl stearate significantly promoted NRCB010 N removal and the N2O reduction capacity. In soil microcosm and greenhouse pot experiments, n-hexadecanoic acid decreased N2O cumulative emissions by 34.3 % and 46.6 %, respectively, and further decreases were observed when combined with NRCB010. Additionally, n-hexadecanoic acid, both independently and in combination with NRCB010, significantly promoted tomato growth. N-hexadecanoic acid, alone or with NRCB010, also altered soil microbial communities and nitrogen-cycle functional gene abundance. Structural equation models revealed that n-hexadecanoic acid, either alone or with NRCB010, decreased N2O cumulative emissions by modifying the environmental conditions to be more conducive to N2O mitigation (e.g., higher soil pH and organic matter content), inhibiting N2O production (through a decrease in ammonia-oxidizing bacteria and nirK gene copy numbers), and promoting N2O reduction (by increasing nosZII gene copy numbers). Our results support the potential use of n-hexadecanoic acid in enhancing crop productivity and mitigating N2O emissions in agricultural soils.