1	Moisture Controls on Trace Gas Fluxes From Semiarid Soils Dean A. Martens and Jean E. T. McLain SWRC – Tucson and Water Conservation Laboratory – Phoenix
2	Semiarid Concepts Due to limited rain and high seasonal temperatures that limit plant productivity, semiarid systems are not important in global C dynamics? Semiarid ecosystems do not contribute to or mitigate atmospheric C concentrations involved in potential climate disruptions
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4	Vegetation Response to Seasonal Moisture
5	Three Vegetation Sites
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7	"Organic"
8	Ambient CO₂ Response to Rainfall
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12	Methane Oxidation with Soil Depth
13	Impacts of Grazing on CH₄ Oxidation
14	Nitrous Oxide Fluxes 2002 – 2003
15	δ¹⁵N₂O Flux From Mesquite
16	Greenhouse Gas Production 2002 monsoon season averaged 303 mg CO₂ equivalents m^-2 (57 d) Cool season averaged 390 mg CO₂ equivalents m^-2 (307 d) 2003 monsoon season averaged 185 mg CO₂ equivalents m^-2 (57 d) 60% reduction of warm season rain reduced CO₂ equivalents by 39%
17	Implications Recent work has emphasized the increased contribution of terrestrial C sources to atmospheric C pools if temperatures increase – positive feedback to climate change For the SW region, climate change models differ on whether future climate scenarios will be wetter or drier and possible shifts from summer to winter rains
18	These Results Suggest If rainfall shifts to greater winter events, overall reductions in surface dominated CO₂ and N₂O fluxes and prolonged spring CH₄ subsurface oxidation Higher warm season precipitation will increase CO₂ and N₂O fluxes due to rapid oxidation of labile C pools that would not be off set by higher CH₄ oxidation rates