Abstract: Grain size features of biological soil crusts and its subsoil in the northern margin of Hobq Desert at different developmental stages are studied by the method of particle-size analysis in this article. The fine sand and medium sand dominate the drifting sand and algal crust surface, and the fine sand and very fine sand prevail on the surface of moss crusts. The content of clay, medium silt, coarse silt and very fine sand on the crust surface are much more than that of same samples under the crust. The moss and algal crusts are very poor in sorting feature, however, soil under the crust is medium. Moreover, curves of drifting sand, moss crust and algal crust are all asymmetric in positive skewed distribution. The peaky curves of moss crust and algal crust are moderate, but that of drifting sand is very sharp. Therefore, soil formation effect of biological crust displays the difference and complexity at the different developmental stages and depth of the soil.

Key words: grain size, biological soil crusts, Hobq Desert