Soil fertility is a key factor in agricultural productivity. Saline–alkali (SA) soils negatively affect plant growth. This article examines the impact of medicinal plants, particularly tiger nut (Cyperus esculentus L.), on soil fertility, as well as the mitigating effects of nanomaterials (nano-selenium, multi-walled carbon nanotubes) and arbuscular mycorrhizas (AMs) on stress. Results indicate that medicinal plants and their symbiotic interactions, along with nanomaterial application, enhance soil nutrient content, improve plant photosynthesis and yield. This approach offers an effective strategy for utilizing saline–alkali soils in agriculture.