Abstract: The soil respiration rates of sandy soil (Ust Sandic Entisols) and sandy loam soil (Los Orthic Entisols) with and without the coverage of mossdominated biological soil crusts (moss crusts) were measured by a portable CO₂ analyzer (LI-840) in a small watershed on the Loess Plateau of China. The effects of moss crusts on soil respiration were determined by the differences of soil respiration rates with and without moss crusts. The results showed that, on hourly scale, the soil respiration rates of the two soils without moss crusts had similar peak values at 14:00, which were 2.49 and 2.66 μmol·m^-2·s^-1, respectively. The presence of moss crusts decreased the soil respiration rates of the two soils by 8.6% and 5.8%, respectively. On daily scale, the daily soil respiration rates of the sandy soil and sandy loam soil were 9.1% and 5.3% lower with moss crusts than those without moss crusts, respectively; while with the presence of moss crusts, the daily soil respiration rate of the sandy soil was 7.1% lower than that of the sandy loam soil. In addition, the soil respiration rates of the two types of soil had a significant relationship with surface (2 cm) soil temperature, implying that surface soil temperature had important influences on the respiration of the two soils with and without moss crusts. Therefore, we speculated that the moss crusts possibly decreased the soil respiration rate through their effect of decreasing soil surface temperature, with an average reduction of 0.3-0.5 ℃ during the experiment. In conclusion, the moss crusts, especially developed on sandy soil, significantly decreased soil respiration on the Loess Plateau of China. Thus, biological soil crusts should be considered in the regional estimation of CO₂ flux and carbon cycling in the Loess Plateau of China and other similar environments.

Key words: remote sensing measures, oceanic primary productivity, phytoplankton absorption coefficient, estimation models