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This study aims to examine the changes in the spatial heterogeneity of soil properties at different soil layers, the spatial heterogeneity of soil and vegetation characteristics along an ecotone, and soil-vegetation relationships along the ecotone in a critical area of desertification.

A study site was established across a Lespedeza potaninii (dominant) community (LPC) and an Artemisia ordosica (dominant) community (AOC), with the ecotone between these two communities. In this study, "along the ecotone" means from LPC, via the ecotone, and then to AOC. Three parallel transects (300-m long) were arranged at 50-m intervals along the site. Along each transect, at 10-m spacings, 1 m x 1-m quadrats were marked for the vegetation survey and soil sampling. Soil samples were analyzed in the laboratory after natural air-drying. Data analyses were conducted with a combination of classical and geostatistical methods.

In most cases, species importance values and soil properties changed significantly (P < 0.05) along the ecotone. Most soil and vegetation variables were moderately spatially autocorrelated. Kriging interpolated maps showed patch patterns of soil chemical properties. The C/(Co + C) values of soil properties were larger at 5-10-cm than those at 0-5-cm. Vegetation characteristics were mainly positively correlated with soil organic carbon (SOC), total nitrogen (TN), and electrical conductivity (EC). TN at 0-5-cm (TN1), EC at 0-5-cm (EC1), and available potassium at 5-10-cm (AK2) were selected as the predictors for plant species richness and diversity in the stepwise regression analysis between vegetation characteristics and soil properties.

Soil nutrients decreased significantly (P < 0.05) along the ecotone. Soil and vegetation properties had moderate spatial heterogeneity. Soil properties had a stronger spatial heterogeneity at subsurface layers compared to surface layers. TN1, EC1, and AK2 were the predominant factors for the plant community structure along the ecotone in the critical area of desertification.