Soil cycling of trace gases in response to mesquite management in a semiarid grassland

Over the last century, proliferation of velvet mesquite (Prosopis velutina) in Southwestern grasslands has led to mesquite removal to increase livestock forage, but the effects of mesquite on the fluxes of C- and N-based gases are not well understood. We report soil surface fluxes and porespace concentrations of carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) over two monsoon seasons beneath mesquite canopy (LIVE), in open grassland (OPEN), and under a mesquite skeleton (DEAD) in Southeastern Arizona. In 2003, CO2 production was not different among sites, but on three 2004 measurement dates, CO2 production was greatest from LIVE. In both years, N2O production was highest in LIVE in early monsoon, while CH4 production dominated in OPEN and DEAD sites. CH4 consumption increased in all sites as the summer progressed, resulting in net monsoon CH4 fluxes near zero. Over both years, temperature and precipitation accounted for significant variability in CO2 flux and precipitation correlated with N2O production. Soil moisture accounted for significant variability in CH4 flux in 2003. Observed variations in trace gas dynamics suggest that several years of measurements would be required to accurately predict mesquite management effects on trace gas flux in Southwestern rangelands.