Improvement of wheat productivity and soil quality by arbuscular mycorrhizal fungi is density- and moisture-dependent

Adaptive management of arbuscular mycorrhizal fungi (AMF) provides a new option for sustainable agriculture. Previous studies showed that the functional role of AMF was frequently dependent on soil moisture and planting densities in the semiarid environment. However, a systematic quantitative analysis of the effects of AMF inoculation on crop productivity and soil quality needs to be investigated. Therefore, a 2-year field experiment was conducted to test the inoculation effects of AMF (Funneliformis mosseae) on wheat (Triticum aestivum L.) productivity and soil quality in the semiarid Loess Plateau under two water regimes (irrigated and non-irrigated) with seven plant densities in year 2017 and 2018. Our results showed that in the non-irrigated treatment, inoculation with AMF greatly increased dryland wheat aboveground biomass, crop productivity, water use efficiency, rhizosphere soil organic carbon, soil organic carbon to total nitrogen ratio, microbial biomass carbon to nitrogen ratio, and microbial biomass carbon and nitrogen (P < 0.05) compared to the non-inoculated treatment. For example, compared with non-inoculated plants, the grain yield in the non-irrigated but inoculated plants increased by 59 ± 28% in 2017 and 36 ± 2.8% in 2018, and the water use efficiency for grain increased by 53 ± 26% and 25 ± 12% in 2017 and 2018, respectively. However, the different results were observed under irrigated conditions. In the irrigated treatment, AMF inoculation had a slightly positive effect on grain yield and soil quality at low plant density but was negative at higher plant densities. Here we demonstrated for the first time that AMF inoculation significantly improved wheat productivity and soil quality, while its effects were conditionally density- and moisture-dependent. Therefore, optimizing AMF addition is an effective measure for sustainable agricultural development and provides a novel solution for the management of soil degradation management in the semiarid area of the Loess Plateau.