A distinctive root-inhabiting denitrifying community with high N2O/(N2O+N2) product ratio

Microbial denitrification in agriculture makes a considerable contribution to terrestrial nitrous oxide (N2O) emissions, and the prevailing view is that this mainly occurs in soil. Here, we show the root N2O emission capacity of wheat grown under three long-term (32-year) fertilization regimes, and compare root-, rhizosphere- and soil-inhabiting denitrifying microbial communities. The N2O/(N2O + N2) product ratio of denitrification in the root was 0.5–9.2-fold higher than that in surrounding soil under fertilized conditions, especially manure application. Root N2O/(N2O + N2) ratio was closely related to the proportion of two nitrite-reductase genes (nirK/nirS), with higher N2O emission associated with increased nirS abundance. Rhodobacterales and Pseudomonadales dominated the root-associated nirS community. In contrast, soils showed a higher proportion of unclassified denitrifiers. Our results demonstrate the potential of wheat to emit N2O from the roots that harbour low-complexity denitrifying communities distinct from those occurred in soils.