AMFc propagation cycles

More extensive and wide-spread use of arbuscular mycorrhizal fungi (AMF) as a biofertilizer in agriculture requires the propagation of AMF spores with a host plant. This propagation however is hardly done under sterile condition and, therefore, will carry microbes associated to the plant, the substrate, and the AMF itself in the inoculum. Thus, understanding the complex interactions among arbuscular mycorrhizal fungi (AMF), plant hosts, and their associated microbiomes (AMF accompanying microbes and plant rhizosphere) is crucial for harnessing the full potential of AMF as biofertilizers. This study investigates the impact of AMF propagation on their associated microbiomes and how those changes impacted their joint capability to promote plant growth. We evaluated the plant growth promotion traits of indole-3-acetic acid (IAA, as promoter of root growth) production and solubilization of inorganic phosphate across 11 cycles of AMF propagation in millet. Our control treatment consisted of the stochastic community composed by the microbes originated from the millet seeds and the greenhouse. This stochastic community served as the background microbiome that will interact with the AMF-inoculated treatment. Our results showed that, AMF-associated microbiomes consistently enhance IAA production, exhibiting context-dependent effects. When the stochastic microbial IAA production is low, inoculation of AMF+accompanying microbes communities augment it, while stabilizing it when stochastic communities produce higher levels. This suggests that AMF communities offer more reliable IAA production, potentially through cooperative microbe recruitment with the plant host. In contrast, AMF's influence on phosphate solubilization is limited compared to stochastic communities. The microbial diversity introduced by stochastic communities significantly impacts phosphate solubilization, while AMF propagation remains relatively insensitive to diversity changes. Bacterial diversity in AMF-associated microbiomes correlates with root biomass changes, indicating their potential role in plant growth promotion. The study highlights the multifaceted contributions of AMF and their associated microbiomes in enhancing plant growth and buffering against variability introduced by new millet seeds. Overall, this research provides insights into the significance of AMF propagation in optimizing soil microbiome stability and nutrient cycling, emphasizing the potential for harnessing AMF-associated microbes in agriculture for consistent and efficient plant growth promotion.