Arbuscular mycorrhizal mycelial networks and glomalin-related soil protein increase soil aggregation in Calcaric Regosol under well-watered and drought stress conditions

Arbuscular mycorrhizal (AM) fungi have a direct influence on soil aggregation in most fertile ecosystems. This study investigated the effects of AM fungi on soil aggregate stability of Calcaric Regosol under well-watered and drought stress conditions. A two-compartment system was employed to exclude the effects of plant roots, and ultrasonic dispersion technique was applied to evaluate the aggregate bond energy. The results showed that good symbiotic relationships were formed between AM fungi and sandstorm-tolerant species Astragalus adsurgens Pall even under drought stress conditions. Inoculation with AM fungi significantly improved plant growth, especially the root development. Hyphal length, spore density, glomalin-related soil protein content were significantly increased by AM fungal inoculation under both well-watered and drought stress conditions. Likewise, the proportion and dispersive energy of soil water-stable macroaggregates were also markedly increased by the inoculation. The hyphae of AM fungi directly contributed to the dispersive energy of soil water-stable macro-aggregates and significantly improved soil aggregate stability under both experimental conditions. This study demonstrates that AM fungi play a dominant role in the stability of soil water-stable aggregates by improving the aggregate bond energy, particularly for macroaggregates.