Embedded Biochar–AMF Technology with Optimized Pore Architecture: A Sustainable Approach to AMF Spore Propagation in Sandy Soils

Mycorrhizae are symbiotic associations between the roots of vascular plants and fungi that facilitate the uptake of water and nutrients by host plants. However, current arbuscular mycorrhizal fungi (AMF) cultivation methods including sand culture, root organ culture, and aeroponics are complex and time-consuming. Moreover, these methods produce low spore yields hindering large-scale production and sustainable application of MF in agriculture. This study systematically evaluated the effects of biochar amendment on the propagation of AMF spores in sandy soils, focusing on how different biochar application rates influence AMF spore density and related soil physicochemical properties. The results showed that increasing biochar concentration led to higher soil pH and EC, suggesting enhanced microbial activity and dynamic adjustments in soil chemical conditions. A typical biphasic response was observed. At low biochar concentrations (approximately 1–1.8%), soil porosity, organic carbon content, and trace element availability were improved, thereby promoting AMF spore formation and hyphal growth. However, concentrations exceeding 2.5% induced physicochemical stress that inhibited fungal propagation. Polynomial regression analysis (R2 = 0.996) confirmed a strong correlation between biochar concentration and AMF spore density, clearly capturing a promotion–plateau–inhibition pattern. In addition, SEM imaging revealed that AMF hyphae adhered to the porous surface of biochar, forming stable hyphal networks that enhance nutrient transport and contribute to rhizosphere microenvironmental stability.