Ecoenzymatic stoichiometry and microbial nutrient limitation in response to shrub planting patterns and arbuscular mycorrhizal fungal inoculation

Arbuscular mycorrhizal fungi (AMF) can form a beneficial symbiotic relationship with shrubs, thereby playing a crucial role in enhancing the stability and sustainability of fragile arid and semiarid ecosystems. How will soil microbial metabolism change from monoculture to the mixed planting of shrubs? What regulatory role will AMF play in this process? Monoculture and mixed planting of three native shrubs were carried out, and treatments with and without AMF inoculation were established at the same time. The indicators of soil microorganisms, extracellular enzymes and nutrients were measured. The variations in ecoenzymatic stoichiometries, microbial nutrient limitations and regulatory factors were also analyzed. The ratio of soil microbial biomass C to N decreased significantly from the monoculture to the mixed planting of shrubs. The ratios of C- and P-acquiring enzymes and N- and P-acquiring enzymes increased in the mixed planting treatment. The microbial P limitation in the monoculture treatment was replaced by microbial N limitation in the mixed planting treatment, and the soil microbial C limitation increased in the mixed planting treatment. AMF inoculation mainly regulated the ecoenzymatic stoichiometric ratios and microbial nutrient limitations in the monoculture treatment but had little effect on the mixed planting treatment. The main factors influencing microbial C limitation were shrub species and AMF richness in the monoculture and mixed planting treatments, respectively. Soil available nutrients and AMF richness and diversity were identified as the main factors influencing microbial P limitation in the monoculture treatment compared with microbial N limitation in the mixed planting treatment. AMF inoculation and the mixed planting of shrubs effectively promoted soil nutrient cycling, which is highly important for restoring arid and semiarid vegetation.