Denitrifiers and Nitrous Oxide Emissions from a Subtropical Vegetable Cropland

Abstract

Anthropogenic emission of nitrous oxide (N2O) is attributed mostly to the application of nitrogen fertilizers in the agricultural sector. Along with the rapid growth of population and the need for foods, the influence of N2O is expected to further increase in the near future. However, studies on the links between N2O emissions and microbial community at a farmland scale are limited. We present the N2O eddy covariance data set from a Chinese cabbage farmland in Taiwan, a subtropical region. Our results reveal that N2O fluxes from soils are elevated during the daytime and decrease at night. Fertilization and the soil temperature significantly affected the microbial community throughout the cultivation periods, leading to an increased abundance of denitrifiers. Moreover, it was found that among the known taxa, Bradyrhizobium and Luteimonas bacteria were among the most abundant denitrifiers, in particular, the fertilization periods, which could be responsible for the high production of N2O because of their incomplete denitrification pathways. The total N2O-N efflux in this study accounts for 2.3-2.5% of the nitrogen in the fertilizers, which is significantly higher than the IPCC default parameter of 1%. We synthesized a data set of N2O eddy covariance measurements and found that the emission of N2O from soils exhibits an exponential increase with the density of N-fertilizers applied. The results underline the significance of N2O emissions from fertilized soils, which are significantly underestimated in the current national emission inventories of greenhouse gases. Moreover, the results shed light on the microbial and physical technology to reduce N2O emissions.