Effects of an arbuscular mycorrhizal fungus on Amorpha fruticosa roots and soil preferential flow in an arid area of opencast coal mine waste

Preferential flow plays a key role in soil hydrological processes in arid and semi-arid areas of opencast coal mine waste. Inoculation with arbuscular mycorrhizal (AM) fungi can significantly affect vegetation root growth and improve soil physical structure. However, the impact on preferential flow in new areas of waste remains poorly understood. Here, the effects of AM fungal inoculation on root spatial distribution and preferential flow within the waste area at Heidaigou opencast coal mine in China were analyzed where Amorpha fruticosa was grown for revegetation. A staining tracer method and a grid sampling method were used. Preferential flow pathway development in the newly formed waste areas was affected mainly by A. fruticosa root systems, with closer proximity to A. fruticosa resulting in more preferential flow pathways. Inoculation with the AM fungus Funneliformis mosseae significantly increased preferential flow development. In the profile closest to the A. fruticosa, the dye coverage increased by 59 %, the uniform infiltration depth by 73 %, and the maximum stained depth by 80 %. Plant roots occurred mainly at 0−20 cm soil depth, accounting for ∼ 80 % of the total root length of the entire root system. In the profile closest to A. fruticosa, inoculation with F. mosseae increased the total number of roots and the root length density by 32 %. The preferential flow pathways were developed only in roots with diameters of > 2 mm and more widely distributed at both 0−10 and 10−20 cm soil depths. Substrate infiltration was influenced mainly by roots with diameters of < 4 mm but deep infiltration was more dependent on roots with diameters > 2 mm. Mycorrhizal hyphae contributed to the preferential flow. Inoculation with the AM fungus increased the preferential flow of the newly formed drainage sites and this effect should be considered in the ecological restoration of opencast coal mine wastes in arid and semi-arid areas.