During the rainless season, arid soils exhibited large diurnal fluctuations in carbon and nitrous oxides emissions, while displaying a uniform pattern of methane emissions throughout the day. 

Abstract

Drylands, constituting approximately 56% of the Earth's terrestrial surface, stand as the largest biome. Despite their vast expanse, our understanding of soil trace gas emissions from these regions remains limited. This knowledge gap arises from an uneven distribution of soil trace gas flux measurements across continents. While North American and East Asian drylands have been extensively studied, reports from other drylands are scarce. This lack of information hinders our ability to effectively constrain the atmospheric budget of reactive carbon and nitrogen gases and to develop predictive models for changes in soil trace gas emissions amid ongoing global environmental changes. To address this gap, we conducted a comprehensive study in the Negev Desert, Israel, utilizing an array of seven automatic soil static chambers coupled to two infrared gas analyzers. This allowed us to measure soil emissions of methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) near-continuously every 15 minutes over three rainless months, measuring ~5000 individual soil fluxes. Our focus was on bare soils with varying organic carbon content (0.2%, 0.5%, and 0.6%) and nitrogen content of ~0.1%. Our findings reveal significant diurnal variations in both CO2 and N2O emissions. CO2 emissions peaked at noon (1318.2±440.4 µg C m-2min-1) and reached their lowest point at midnight (373.4±228.8 µg C m-2min-1). In contrast, soil N2O flux was highest at 9:00 (0.07±0.02 µg N m-2min-1) and lowest at 21:00 (0.03±0.01 µg N m-2min-1). Soil CH4 flux exhibited minimal variation, with maximum and minimum emissions of 0.43±0.24 and 0.16±0.09 µg C m-2min-1, respectively. Notably, the distinct peak emission times for CO2 and N2O suggest different underlying mechanisms for the production of these gases in the soil. Furthermore, we observed a strong correlation between soil CO2 emissions and soil water fluxes, while all gaseous fluxes correlated with the organic carbon content of soils. This emphasizes the role of water and soil organic carbon as primary driving factors for trace gas production in desert soils during rainless periods. Specific mechanisms of soil trace gases production in dry desert soils, however, will require further research.