| A long-term mass balance model was used to estimate a lower limit for nitrogen loss from deserts in the southwestern US. Loss of nitrogen to the atmosphere was calculated to be {dollar}geq{dollar}77% of the atmospheric inputs.; A factorial experiment demonstrated that N loss by denitrification in a desert ecosystem was influenced by a carbon/nitrogen interactive effect and by the availability of water. No evidence for NO{dollar}sb3sp{lcub}-{rcub}{dollar} limitation in moist cores was found.; Denitrification rates in wet desert soil (ca. 32.9 ng-N/cm{dollar}sp2*{dollar}hr) are similar to those in more mesic ecosystems. Extrapolated to an annual basis denitrification is ca. 7 kg-N/ha{dollar}*{dollar}yr.; The content of denitrifying enzymes in desert uplands was strongly associated with indices of N and C availability. A significant fraction of the enzyme content in wet desert soil is derived from a persistent pool of enzymes capable of tolerating desiccation. The synthesis of new enzymes involves a complex interaction between available C, N, and soil moisture.; The activity of denitrifying enzymes in desert soil was optimal at 40{dollar}spcirc{dollar}C and a pH of 7.0. The Q{dollar}sb{lcub}10{rcub}{dollar} was 1.74, and the activation energy was about 9807 cal mol{dollar}sp{lcub}-1{rcub}{dollar}. Enzyme activity in freshly wet soil was not limited by NO{dollar}sb3sp{lcub}-{rcub}{dollar}, and only slightly limited by C availability.; A soil texture gradient distinguished between the different deserts and landforms (bajadas and playas) that were sampled. Sandy soils were associated with low soil organic matter and, to a lesser extent, low indices of N and C turnover.; A strong correlation between potential mineralization and nitrification (r{dollar}sp2{dollar} = 0.94) was found in desert soils. The content of denitrifying enzymes was correlated to indices of both C (r{dollar}sp2{dollar} = 0.73) and NO{dollar}sb3sp{lcub}-{rcub}{dollar}-N (r{dollar}sp2{dollar} = 0.74) availability.; Most of the N lost by denitrification in deserts is probably in the form of N{dollar}sb2{dollar}O. An estimated loss of 2.9-18.35 {dollar}times{dollar} 10{dollar}sp{lcub}12{rcub}{dollar}g of N{dollar}sb2{dollar}O-N. from the arid lands of the world would comprise a significant terrestrial source. |
