Microbial process-oriented understanding of stimulation of soil N2O emission following the input of organic materials

Although crop residue return increases upland soil emissions of nitrous oxide (N2O), a potent greenhouse gas, the mechanisms responsible for the increase remain unclear. Here, we investigate N2O emission pathways, gross nitrogen (N)-cycling rates, and associated N-cycling gene abundances in an upland soil following the addition of various organic material under aerobic incubation using a combination of N-15 tracing technique, acetylene (C2H2) inhibition, and real-time PCR (qPCR) methods. Increased total N2O emissions following organic material amendment was attributed to both increased nitrification-derived N2O emissions, following increased ammonia-oxidizing bacteria (AOB)-amoA abundance, and denitrification-derived N2O emissions, following increased nirS and decreased nosZ abundance. Increasing plant residue carbon (C)/N ratio decreased total N2O emissions by decreasing the contribution of denitrification to N2O emissions, potentially due to higher proportions of denitrified N emitted as N2O than nitrified N emitted as N2O. We further propose a novel conceptual framework for organic material input effects on denitrification-derived N2O emissions based on the decomposable characteristics of the added organic material. For slowly decomposing organic materials (e.g., plant residue) with insufficient available C, NOT-N immobilization surpassed denitrification, resulting in gradual decrease in denitrification-derived N2O emissions with an increase in mineralization of plant residue C losses. In contrast, available C provided by readily available C sources (e.g., glucose) seemed sufficient to support the co-occurrence of NOT-N immobilization and denitrification. Overall, for the first time, we offer a microbial process perspective of N2O emissions following organic material input. The findings could facilitate the improvement of process-orientated models of N2O emissions and the formulation of appropriate N2O mitigation strategies for crop residue-amended soils. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The study found that the increase in N2O emissions in soil after adding plant residue was mainly due to increased emissions from nitrification and denitrification sources. Furthermore, an increase in the carbon/nitrogen ratio of plant residue can decrease total N2O emissions by reducing the contribution of denitrification to N2O emissions.