干旱区生态环境知识资源中心

A survey of nitric oxide (NO) emission from Chihuahuan desert soils found mean NO fluxes < 0.1 ng NO-N cm(-2) h(-1) during the dry season. These fluxes were at the lower end of the range reported for temperate grassland and woodland ecosystems. NO fluxes from wet or watered soils were higher (0.1-35 ng NO-N cm(-2) h(-1)). Watering of black grama grassland soils produced an initial pulse of 12 ng cm(-2) h(-1) (12-h after 1-cm watering) with high fluxes sustained over 4 days with repeated watering. Initial pulses from shrubland soils were lower (maximum 5 ng cm(-2) h(-1)), and fluxes declined with repeated watering. Repeated watering of creosotebush soils depleted the soil NH4+ pool, and NO emissions were directly related to soil NH4+ concentrations at the end of the experiment. In watered and NH4+-fertilized creosotebush soils, NO fluxes were positively related to potential net nitrification rates. NH4+-fertilization boosted the initial NO pulse 15 times in the shrubland and 5 times in black grama grassland relative to watered controls. These experimental results point toward greater substrate limitation in shrublands. In this desert basin, NO emission averaged 0.12 kg N ha(-1) y(-1) in untreated soil and 0.76 kg N ha(-1) y(-1) in watered soil. We multiplied these averages by the distribution of grassland and shrubland vegetation within a 58,600-ha area of the Jornada del Muerto basin to estimate regional losses of 0.15-0.38 kg NO-N ha(-1) y(-1) for this area of the Chihuahuan desert.