Objective Northwestern Liaoning province, as a typical ecologically vulnerable area on the southern edge of the Horqin Sandy Land, faces constraints on regional ecological reconstruction due to land desertification leading to soil erosion and inefficient water resource utilization. Soil preferential flow is a key process in regulating water and nutrient movement in this area, and its characteristics have essential guiding value for vegetation restoration and water resource management.

Methods This study focused on the grasslands in northwestern Liaoning province with no desertification (ND), light desertification (LD), moderate desertification (MD), and heavy desertification (HD), and used dye tracing experiments to reveal the distribution and morphological variation patterns of preferential flow under the desertification gradient, and to clarify the mechanism of the impact of desertification on preferential flow.

Results 1) The horizontal distribution of soil preferential flow in desertified grasslands was predominantly bimodal, and the preferential flow pattern presented asymmetry. 2) As the soil depth increased, the stained area ratio of preferential flow decreased. The matrix flow depth ranged from 10.22 cm to 27.78 cm, the maximum staining depth ranged from 54.78 cm to 56.11 cm, and the stained area ratio ranged from 46.80% to 63.87%. 3) The variation of preferential flow stained patterns (paths) showed significant stratification. The variation coefficient of the stained area ratio in the 0−50 cm soil layer was relatively small, but it increased sharply below 50 cm, showing an activity gradient of "relatively stable–moderately active–active–rapidly changing" in the vertical direction, and the degree of desertification significantly reduced the activity of preferential flow. 4) The stained area ratio was highly positively correlated with root indicators (P < 0.01), with a correlation coefficient ranging from 0.31 to 0.65, where the root diameter had the most significant impact on preferential flow.

Conclusions The desertification of grasslands will reduce the activity of preferential flow in the soil, and the root system is the main factor affecting the preferential flow in the desertified grasslands of northwestern Liaoning province.