|Mcclaran, Mitchel - UNIV OF ARIZONA|
Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: September 15, 2006
Publication Date: November 16, 2006
Citation: Mclain, J.E., Martens, D.A., Mcclaran, M.P. 2006. Does Mesquite Growth and Removal Impact Net Greenhouse Gas Emissions in Southwestern Rangelands?. Agronomy Abstracts. [CD-ROM P24750] Technical Abstract: The encroachment of velvet mesquite (Prosopis velutina) has resulted in increased N inputs to Southwestern rangeland soils. Because woody plant proliferation threatens the sustainability of livestock grazing, however, control of mesquite has been advocated as a means to increase rangeland forage production. The influences of mesquite control on the fluxes of CO2, N2O, and CH4 have been poorly characterized to date. This study reports soil trace gas fluxes under established mesquite (11.4 mg C cm-3), open grassland (6.1 mg C cm-3), and 40-year old mesquite stumps (7.9 mg C cm-3) in southeastern Arizona over 2 monsoon seasons. During the 2003 monsoon (170 mm total rainfall), differences in soil C content did not correlate with variations in CO2 production, and efflux averaged 180.4 mg CO2 m-2 h-1 over all sites. In 2004, lower rainfall (111 mm) corresponded with increased (30%) CO2 emissions beneath mesquite, while efflux in the open and stump plots decreased by 40%. N2O emissions averaged 13.6 (mesquite), 5.7 (open), and 6.8 'g N2O m-2 h-1 (stump) during the 2003 monsoon, but increased by more than 40% across all sites in 2004. Mesquite soils showed a steady (-17.4 'g CH4 m-2 h-1) CH4 sink across both seasons, while the open and stump sites showed early-monsoon CH4 production, possibly due to belowground termite activity. As the monsoon progressed, these CH4 sources turned into small (-6.2 'g CH4 m-2 h-1) sinks. Global warming potentials (GWPs) of all sites were strongly dominated by CO2 efflux. Given adequate rainfall, mesquite control measures did not impact the GWP of semiarid soils. Under limited rainfall, however, grassland and stump sites had GWPs 40% lower than that of the mesquite, indicating that climate change shifts resulting in reduced monsoon precipitation may contribute to negative feedbacks for future global warming.