Abstract: This paper studied the spatial distribution of arbuscular mycorrhizal (AM) fungi in Astragalus adsurgens root-zone soil in Mu Us sand land under five different ecological conditions. The results showed that the colonization and spore density of AM fungi differed significantly with sampling sites and soil depths. The highest colonization rate and spore density of AM fungi were found in 10-30 cm soil layer, and the highest spore density was at Dingbian site. Ningtiaoliang and Tawan sites had the highest vesicular colonization, and Tawan site had the highest total and hyphal colonization. The contents of total glomalin (TG) and easily extractable glomain (EEG) were the highest at Tawan site, being 1.18 mg·g^-1 and 0.65 mg·g^-1, respectively. Soil pH had significant positive effects on the vesicular and arbuscular colonization, spore density, TG, and EEG, and the TG and EEG had significant positive correlations with spore density, soil organic carbon (SOC), and soil available N and P. The proportion of glomalin to SOC was higher in desert soils than in agricultural soils, which implied that glomalin could be one of the main origins of SOC in desert ecosystem. Therefore, glomalin could be a useful index for the evaluation of soil AM fungal activity and soil ecology.

Key words: support vector machine regression (SVR), organic carbon, particle swarm optimization (PSO), soil