Effect of AMF inoculation on root distribution and water use efficiency of Amorpha fruticosa L in western coal mining area

Coal mining in arid and semi-arid areas has led to the emergence of large areas of coal mining subsiding areas. The ecological reclamation of mining areas is hard, and the mycorrhizal microbial technology for ecological restoration has become a current research hotspot. To investigate the effects of arbuscular mycorrhizal fungi (AMF) inoculation on the root distribution characteristics and water use efficiency (WUE) of Amorpha fruticosa L. Three experimental treatments were set up: control without planting A fruticosa L seedlings (CK1), planting A fruticosa L seedlings (CK), planting A fruticosa L seedlings and inoculated with AMF (+AM). The plant growth indicators and soil moisture were measured, and the results showed that: ① AMF inoculation effectively promoted the growth of A fruticosa L. Compared with CK treatment, the plant height, SPAD value, aboveground biomass and aboveground biomass increased by 38.5%, 27.5%, 11.1% and 69.4%, respectively; ② Inoculation changed the root distribution of A fruticosa L and increased the total root length and the number of root tips by 329.0% and 586.1%, respectively. Besides, reduced the average root diameter by 22.9%, and increased the proportion of fine roots below 2 mm by 370.1%. At the same time, inoculation affected soil water distribution and water use pattern of A fruticosa L. Compared with CK treatment, the soil water content of 0-20 cm increased by 8.9% and 7.8%, and the soil water content of 20−50 cm decreased by 16.8%, 4.0% and 11.6%, respectively. The water use ratio of A fruticosa L to soil below 5 cm was increased by 15.4% and 9.9% at 5-30 cm and 30-50 cm, respectively; ③ Inoculation increased the WUE of A fruticosa L by 27.5%. The results of principal component analysis showed that fine root length (0.5−1.00 mm) and root tip number in the roots of A fruticosa L were the key root characteristics for the efficient use of soil water by AMF inoculation under drought stress. In conclusion, inoculation with mycorrhizal fungi can significantly promote the growth of A fruticosa L seedlings, promote the absorption and redistribution ability of soil water through the significant improvement of the fine root characteristic parameters of A fruticosa L, and then make A fruticosa L plants show a high WUE. The results of this study can provide a scientific guidance and technical support for the biological combined remediation technology in the western coal mining settlement area.