Abstract: To better understand the distribution patterns of microorganisms in biological crusts in semiarid sandy region, measurements were made on the quantities of microorganisms in the biological crusts in southern Mu Us sandy land. From the top of sand dune to the inter-dune, the total umber of the microorganisms had an increasing trend, and had significant difference in the crust layer at different geomorphic locations (P<0.5), except that between the top of sand dune and the windward slope, and between windward slope and lee slope. In the crust layer and the 0-5 cm and 5-10 cm soil layers under crust at the same locations, the vertical distribution of microorganisms varied. Generally, with the deepening depth, the quantities of microorganisms increased after an initial decrease, but the quantities of actinomyces on the windward slope decreasedafter an initial increase, and the quantities of the total number of microorganisms, bacteria, and fungi on the windward slope as well as the quantities of fungi on the top of sand dune decreased continually. Among the microorganism groups, bacteria were predominant, followed by actinomyces, and fungi. The proportion of bacteria in the total number of microorganisms was higher in inter-une than on the top of sand dune, but the proportions of actinomyces and fungi in the total number of microorganisms were opposite. The vertical distribution of microorganisms in the 0-5 cm and 5-10 cm soil layers under crust was in accord with soil moisture content, and accordingly, the latter could be the key factor affecting the vertical distribution of soil microorganisms.

Key words: CO₂, O₃, Interaction, Chloroplast ultrastructure, Soybean