Abstract
Agriculture is the main source of terrestrial emissions of N2O, a potent greenhouse gas and the main cause of ozone layer depletion. The reduction of N2O into N2 by microorganisms carrying the nitrous oxide reductase gene (nosZ) is the only biological process known to eliminate this greenhouse gas. Recent studies showed that a previously unknown clade of N2O-reducers was related to the capacity of the soil to act as an N2O sink, opening the way for new strategies to mitigate emissions. Here, we investigated whether the agricultural practices could differently influence the two N2O reducer clades with consequences for denitrification end-products. The abundance of N2O-reducers and producers was quantified by real-time PCR, and the diversity of both nosZ clades was determined by 454 pyrosequencing. Potential N2O production and potential denitrification activity were used to calculate the denitrification gaseous end-product ratio. Overall, the results showed limited differences between management practices but there were significant differences between cropping systems in both the abundance and structure of the nosZII community, as well as in the [rN2O/r(N2O+N2)] ratio. More limited differences were observed in the nosZI community, suggesting that the newly identified nosZII clade is more sensitive than nosZI to environmental changes. Potential denitrification activity and potential N2O production were explained mainly by the soil properties while the diversity of the nosZII clade on its own explained 26% of the denitrification end-product ratio, which highlights the importance of understanding the ecology of this newly identified clade of N2O reducers for mitigation strategies.
Highlights
Nitrous oxide (N2O) is one of the six gases subject to restriction by the Kyoto Protocol, which aims at reducing anthropogenic greenhouse gas (GHG) emissions
The potential activity of denitrifying microorganisms varied in all cropping systems, ranging from 0.03 (CI95% = [0− 0.09]) to 0.85 (CI95% = [0.79 − 0.91]) and 0.17 (CI95% = [0.07 − 0.27]) to 1.51 (CI95% = [1.41 − 1.61]) μg N2O-N g−1 soil DW h−1 for potential N2O and potential denitrification activity (PDA), respectively (Figures 1A,B)
Abundance of Total Bacteria, N2O-producers and N2O-reducers The genes encoding catalytic enzymes involved in N2O production and N2O reduction were quantified by Real-Time quantitative PCR and used as proxies for the abundances of the corresponding functional communities
Summary
Nitrous oxide (N2O) is one of the six gases subject to restriction by the Kyoto Protocol, which aims at reducing anthropogenic greenhouse gas (GHG) emissions. N2O is both directly and indirectly of importance for the Earth’s climate. It is a potent greenhouse gas with a long life time of 110 years and a global warming potential 298 times that of carbon dioxide on a 100-year time scale and per unit of weight. N2O is the third most important GHG contributing to about 10%. N2O reducers and GHG mitigation of annual global warming (Bates et al, 2008; Thomson et al, 2012). The atmospheric concentration of N2O has been rising over the past 100 years resulting in a concentration 19% higher than preindustrial levels (Montzka et al, 2011) with an estimated increase of N2O emissions of up to 60% by 2050 (relative to 1900 values) (Bouwman et al, 2013)
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