Mechanisms behind soil water evaporation and infiltration during long-term microbial reclamation in coal mining-induced subsidence areas in northern Shaanxi Province, China

Background Water scarcity is identified as an important factor restricting ecological restoration in arid and semi-arid mining areas. The application of microbial reclamation technologies, especially inoculation with Arbuscular mycorrhizal fungi (AMF), has achieved encouraging ecological effects in mining areas. In this case, investigating soil water movement and its controlling factors in mining areas undergoing long-term microbial reclamation is a key scientific issue for understanding the long-term ecological restoration mechanisms of AMF.

Methods This study investigated the microbial reclamation base in the coal mining-induced subsidence area of the Daliuta coal mine of northern Shaanxi Province, located in the middle reaches of the Yellow River. Specifically, it selected Amorpha fruticosa L. quadrats that experienced 10 years of AMF inoculation (AM) reclamation, reclamation without fungal inoculation (CK), and natural restoration (L-CK) each. For each treatment model, three understory coverage levels were used, i.e., high (>60%), medium (30%‒60%), and low (<30%), leading to nine experimental treatments in total. In situ monitoring experiments on soil water infiltration and evaporation processes were carried out using double-ring infiltrometers and micro-lysimeters.

Results and Conclusions The AM treatment model yielded a significant reduction in soil bulk density, as well as increases in soil porosity, organic matter content, and nutrient content (P<0.05), creating favorable conditions for water transport and retention in soils. Compared to the L-CK treatment model, the AM treatment model exhibited decreases of 22.7%, 10.3%, and 1.2% in soil water evaporation and increases of 21.4%, 38.5%, and 125.9% in average soil water infiltration rate under high, medium, and low coverage, respectively (P<0.05). The equation proposed by Fang Zhengsan can effectively reflect the characteristics of soil water infiltration in the study area, with an average coefficient of determination (R²) of 0.94. The key factors influencing soil water infiltration included the organic matter content, bulk density, and total porosity of soils, while the soil water evaporation was governed by soil bulk density, Understory vegetation coverage and organic matter content. Therefore, the long-term microbial reclamation can effectively reduce soil water evaporation and increase water infiltration, enhancing both soil water retention and water-use efficiency in reclaimed areas. This technology holds great potential for long-term ecological reclamation, serving as a practical guide for the ecological reclamation efforts on the principle that water determines planting in coal mining areas within the Yellow River basin.