Abstract
Denitrification in pasture soils is mediated by microbial and physicochemical processes leading to nitrogen loss through the emission of N2O and N2. It is known that N2O reduction to N2 is impaired by low soil pH yet controversy remains as inconsistent use of soil pH measurement methods by researchers, and differences in analytical methods between studies, undermine direct comparison of results. In addition, the link between denitrification and N2O emissions in response to carbon (C) mineralization and pH in different pasture soils is still not well described. We hypothesized that potential denitrification rate and aerobic respiration rate would be positively associated with soils. This relationship was predicted to be more robust when a high resolution analysis is performed as opposed to a single time point comparison. We tested this by characterizing 13 different temperate pasture soils from northern and southern hemispheres sites (Ireland and New Zealand) using a fully automated-high-resolution GC detection system that allowed us to detect a wide range of gas emissions simultaneously. We also compared the impact of using different extractants for determining pH on our conclusions. In all pH measurements, soil pH was strongly and negatively associated with both N2O production index (IN2O) and N2O/(N2O+N2) product ratio. Furthermore, emission kinetics across all soils revealed that the denitrification rates under anoxic conditions (NO+N2O+N2 μmol N/h/vial) were significantly associated with C mineralization (CO2 μmol/h/vial) measured both under oxic (r2 = 0.62, p = 0.0015) and anoxic (r2 = 0.89, p<0.0001) conditions.
Highlights
Nitrous oxide (N2O) is a potent greenhouse gas contributing 8% of anthropogenic global warming [1,2,3] and responsible for depleting stratospheric ozone [4]
It is known that soil pH plays a strong role in regulating the loss of N gases [27]
We tested soil pH using the three most commonly used extractants and found that soil pH measurements vary across all three extractants (Fig 4 and S2 Table)
Summary
Nitrous oxide (N2O) is a potent greenhouse gas contributing 8% of anthropogenic global warming [1,2,3] and responsible for depleting stratospheric ozone [4]. The N2O molecule has a Global Warming Potential (GWP) 298 times higher than carbon dioxide (CO2) over a 100-year period and an atmospheric life of approximately 121 years [3]. Denitrification Kinetics, C Mineralization, and pH in Pasture Soils PLOS ONE | DOI:10.1371/journal.pone.0151713 March 18, 2016
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