Corrigendum: Chemical formation of hybrid di-nitrogen calls fungal codenitrification into question.

This corrects the article DOI: 10.1038/srep39077.

Chemical formation of hybrid di-nitrogen calls fungal codenitrification into question.

Removal of excess nitrogen (N) can best be achieved through denitrification processes that transform N in water and terrestrial ecosystems to di-nitrogen (N2) gas. The greenhouse gas nitrous oxide (N2O) is considered an intermediate or end-product in denitrification pathways. Both abiotic and biotic denitrification processes use a single N source to form N2O. However, N2 can be formed from two distinct N sources (known as hybrid N2) through biologically mediated processes of anammox and codenitrification. We questioned if hybrid N2 produced during fungal incubation at neutral pH could be attributed to abiotic nitrosation and if N2O was consumed during N2 formation. Experiments with gas chromatography indicated N2 was formed in the presence of live and dead fungi and in the absence of fungi, while N2O steadily increased. We used isotope pairing techniques and confirmed abiotic production of hybrid N2 under both anoxic and 20% O2 atmosphere conditions. Our findings question the assumptions that (1) N2O is an intermediate required for N2 formation, (2) production of N2 and N2O requires anaerobiosis, and (3) hybrid N2 is evidence of codenitrification and/or anammox. The N cycle framework should include abiotic production of N2.

Footprint methods to separate N2O emission rates from adjacent paddock areas.

Using micrometeorological techniques to measure greenhouse gas emissions from differently treated adjacent plots is a promising avenue to verify the effect of mitigation strategies at the field scale. In pursuing such an approach, it is crucial to accurately characterize the source area of the fluxes measured at each sampling point. Hence, a comprehensive footprint analysis method is required so that emission rates can be obtained for a specific field within a biochemically heterogeneous area. In this study, a footprint analysis method is developed to estimate the emission for an experiment where the flux of N2O is measured from several control and treated plots. The emission rate of an individual plot is estimated using an inverse footprint fraction approach where the footprint fractions are obtained from an analytical footprint model. A numerical solution for obtaining the background flux for such a multiplot measurement system is also provided. Results of the footprint analysis method are assessed, first, by comparing footprint fractions obtained from both an analytical footprint model and a "forward" simulation of a backward Lagrangian stochastic (bLs) model; and second, by comparing the emission rates of a control plot obtained from the footprint analysis method and from the "backward" simulation of the bLs model. It is found that the analytical footprint fractions compare well with the values obtained from the bLs model (correlation coefficient of 0.58 and 0.66 within p value <0.001). An average of 4.3 % of the measured fluxes is found to be contributed by sources outside the measured area and, excluding this outside area contribution to the measured flux, footprint corrected emission rates within the defined domain are found to increase by 2.1 to 5.8 % of the measured flux. Also, the proposed method of emission rate estimation is found to work well under a wide range of atmospheric stability.

Population dynamics of type I and II methanotrophic bacteria in rice soils.

Methane-oxidizing bacteria (methanotrophs) consume a significant but variable fraction of greenhouse-active methane gas produced in wetlands and rice paddies before it can be emitted to the atmosphere. Temporal and spatial dynamics of methanotroph populations in California rice paddies were quantified using phospholipid biomarker analyses in order to evaluate the relative importance of type I and type II methanotrophs with depth and in relation to rice roots. Methanotroph population fluctuations occurred primarily within the top 0-2 cm of soil, where methanotroph cells increased by a factor of 3-5 over the flooded rice-growing season. The results indicate that rice roots and rhizospheres were less important than the soil-water interface in supporting methanotroph growth. Both type I and type II methanotrophs were abundant throughout the year. However, only type II populations were strongly correlated with soil porewater methane concentrations and rice growth.