Nitrous oxide emissions in response to wetting dryland soils along a carbon gradient

Soil nitrous oxide (N₂O) emissions from drylands are often suppressed due to low water availability, which limits microbial processes. Nonetheless, high N₂O emissions have been observed after wetting dry desert soils. Because soil C content can affect microbially-driven N₂O production, we hypothesized C content would influence denitrification rates and help explain why some drylands produce N₂O. To test this hypothesis, we are measuring N₂O emissions and changes in the isotopic composition of N₂O (site preference) after rewetting soils from three sites along a gradient in soil C content: i) hand-selected peds rich in organic matter collected from underneath shrubs ("High C"), ii) soils from underneath shrubs (without selecting for C-rich peds; ("Mid C"), and iii) interspaces between shrubs ("Low C"). Our results show that soils obtained from underneath shrubs (Mid C) produce a rapid pulse of N₂O within 5 seconds of adding water, whereas soils from the interspaces (Low C) do not. Furthermore, Fe(II) concentrations determined by anoxic extractions (both 0.3 M CaCl₂ and 2 M HCl) were higher in shrub soils relative to soil from the interspaces, suggesting the rapid production of N₂O may be influenced by rapid abiotic redox reactions involving Fe. Ongoing measurements including nitrification potential, denitrification potential, and site preference of N₂O will be used to understand the mechanisms controlling these fast N emissions from dryland ecosystems.