Carbon emissions from desert soil regulated by non-rainfall water inputs and their potential mechanisms

During periods with no precipitation, desert ecosystem soils periodically absorb air moisture at night to form non-rainfall water inputs (NRWIs), while substantial carbon dioxide (CO₂) emissions are typically observed during midday. However, the intrinsic relationship between these periodic NRWIs and the CO₂ release phenomenon remains unclear. In this study, we utilized biological soil crusts and employed in situ observation methods during the summer and fall. We also conducted humidity- and temperature-controlled experiments to investigate the effects and potential mechanisms of NRWIs and temperature variations on daily soil CO₂ release. We found that soil accumulated NRWIs and soil respiration rates reached their peak values at dawn and midday, respectively, with a lag of 2–4 h between the two. The accumulated NRWIs increased with the development of the crusts across different cover types, however, there was no significant difference in maximum soil respiration rate observed at noon. Notably, the significant release of CO₂ at midday was eliminated when the soil NRWIs were suppressed, demonstrating that the NRWIs were the primary determinant of the substantial CO₂ release at midday. Furthermore, the soil sucrase activity, dehydrogenase activity, microbial richness, and the Chao1 index of soil microorganisms were significantly higher at noon than at night, indicating that microbial activity was greater during the day compared with at night. Our results confirm that the significant midday CO₂ release in desert ecosystems is like a daily “micro-Birch effect” phenomenon induced by NRWIs. This phenomenon may be due to the transition between dormancy and activation of microorganisms mediated by NRWIs. This study demonstrates that NRWIs induce consistent daily pulses of CO₂ in desert ecosystems, representing a previously overlooked microbial-driven pathway. Given the extensive coverage of deserts in global terrestrial ecosystems, this mechanism may have implications for carbon cycling and budget estimates in drylands and potentially at broader scales.