Moisture Controls on Trace Gas Fluxes in Semiarid Riparian Soils

Abstract

Variability in seasonal soil moisture (SM) and temperature (T) can alter ecosystem/atmosphere exchange of the trace gases carbon dioxide (CO 2), nitrous oxide (N 2 O), and methane (CH 4). This study reports the impact of year-round SM status on trace gas fluxes in three semiarid vegetation zones, mesquite (30 g organic C kg 21 soil), open/ forb (6 g organic C kg 21 soil), and sacaton (18 g organic C kg 21 soil) from July 2002-September 2003 in southeastern Arizona. Carbon dioxide and N 2 O emissions were highly dependent on available SM and T. During the heavy rains of the 2002 monsoon (238 mm total rainfall), large differences in soil C content did not correlate with variations in CO 2 production, as efflux averaged 235.6 6 39.5 mg CO 2 m 22 h 21 over all sites. In 2003, limited monsoon rain (95 mm total rainfall) reduced CO 2 emissions by 19% (mesquite), 40% (open), and 30% (sacaton), compared with 2002. Nitrous oxide emissions averaged 21.1 6 13.4 (mesquite), 2.1 6 4.4 (open), and 3.9 6 5.2 mg N 2 O m 22 h 21 (sacaton) during the 2002 monsoon. Limited monsoon 2003 rainfall reduced N 2 O emissions by 47% in the mesquite, but N 2 O production increased in the open (55%) and sacaton (5%) sites. Following a dry winter and spring 2002 (15 mm total rainfall), premonsoon CH 4 consumption at all sites was close to zero, but following monsoon moisture input, the CH 4 sink averaged 26.1 6 6.3 mg CH 4 m 22 h 21 through April 2003. Laboratory incubations showed potentials for CH 4 oxidation from 0 to 45 cm, suggesting that as the soil surface dried, CH 4 oxidation activity shifted downward in the sandy soils. Predicted climate change shifts in annual precipitation from one dominated by summer monsoon rainfall to one with higher winter precipitation may reduce soil CO 2 and N 2 O emissions while promoting CH 4 oxidation rates in semiarid riparian soils of the Southwest, potentially acting as a negative feedback for future global warming.

Riparian Land-Use and Rehabilitation: Impact on Organic Matter Input and Soil Respiration

“…Soil moisture and temperature were thought to be two key factors most closely linked to soil respiration (Pacific et al 2008), and parallel to changes in soil moisture and temperature are seasonal changes leading to variations in soil respiration (Soosaar et al 2011). Soil respiration at Washington Creek had a strong seasonal trend where the greatest activity occurred in the summer, which was also observed in other temperate riparian zones (Raich and Tufekcioglu 2000;McLain and Martens 2006;Picek et al 2007;Pacific et al 2008;Shrestha et al 2009;Audet et al 2013) and between dry and wet seasons in tropical and semi-arid ecosystems (Zanchi et al 2014;Akburak and Makineci 2013). In temperate climates, soil is moist and cool in the spring and autumn, which are unfavorable conditions for microbial activity (Mander et al 2008).…”

“…Riparian zones in temperate as well as tropical environments can therefore be a hotspot for GHG emissions, but their role in the release CO 2 via soil respiration and their C sequestration potential remains insufficiently assessed (Soosaar et al 2011). To date, soil respiration rates from riparian zones were quantified as ranging from 20.6 kg CO 2 ha -1 y -1 in semi-arid or subtropical riparian brush or grassland vegetation (McLain and Martens 2006) to 11,400 kg CO 2 ha -1 y -1 in rehabilitated temperate poplar plantations (Tufekcioglu et al 2001).…”

“…For example, some studies found that soil moisture (McLain and Martens 2006;Soosaar et al 2011) andsoil temperature (Teiter andMander 2005;Soosaar et al 2011) are the driving factors of soil respiration in riparian zones. However, others found that vegetation composition (Hopfensprenger et al 2009) or tree maturity (Bailey et al 2009) plays a greater role in controlling respiration than soil moisture and temperature.…”

Exploring the Relationships between Greenhouse Gas Emissions, Yields, and Soil Properties in Cropping Systems

“…Methane produced from agricultural practices has been found to be emitted biologically via methanogenic bacteria under anaerobic soil conditions [70,71]. Methane has also been found to be consumed in agricultural soils by soil methanotropic bacteria [72]. This phenomenon causes agricultural soils (excluding rice paddies) to be consumers, producers or neutral, depending on the time of season [71].…”

Variability in soil respiration across riparian-hillslope transitions

“…In the standing paradigm of soil water content (SWC)-temperature-CO 2 relationships, soil temperature is considered to be the primary control and SWC the secondary control on soil CO 2 production (defined as the combination of heterotrophic and autotrophic respiration) (Raich and Schlesinger 1992;Raich and Potter 1995;Risk et al 2002a). However, SWC can become the dominant control on soil CO 2 production in very wet (Happell and Chanton 1993;Buchmann et al 1997Buchmann et al , 1998Welsch and Hornberger 2004) or dry (Conant et al 1998(Conant et al , 2004McLain and Martens 2006;Riveros-Iregui et al 2007) environments due to oxygen limitations (Skopp et al 1990) and moisture stress (Orchard and Cook 1983), respectively. It is generally understood that increases in soil temperature (Hamada and Tanaka 2001;Raich et al 2002;Pendall et al 2004) and SWC (Davidson et al 2000;Kelliher et al 2004) promote higher rates of soil respiration, however, the switch from temperature to SWC as the primary control of soil CO 2 production remains poorly understood.…”