Arbuscular mycorrhizal fungi stimulate a trade-off strategies of rhizosphere soil microbiome function for cadmium and phosphorus uptake for two different Cd-hyperaccumulators

Symbiosis with arbuscular mycorrhizal fungi (AMF) enhances Cd accumulation by Cd-hyperaccumulators. AMF interacts with different soil microbiomes in natural and agricultural systems and influences plant nutrient uptake (especially phosphorus, P). However, Under Cd-contaminated and nutrient-stressed soils, the microbial recruitment strategy determining Cd uptake and nutrient absorption (P in particular) in the Cd-hyperaccumulator-AMF symbiont remains unclear. In this study, two types of hyperaccumulating plants with different growth rates (S. nigrum and S. alfredii) inoculated with or without AMF were cultivated in Cd-contaminated soils for 2 months. AMF colonization led to a 21.44%-41.02% rise in the biomass of hyperaccumulating plants and a 1.4-3.0 times increase in Cd extraction. Following AMF colonization, S. alfredii showed a 2.8-fold increase in Cd enrichment compared to S. nigrum, whereas S. nigrum exhibited a 2.9-fold higher P acquisition than S. alfredii. Following colonization by AMF, the concentration of AP in the rhizosphere soil of the S. nigrum markedly diminished, resulting in the formation of a "phosphorus depletion" zone in the rhizosphere, whilst the AP content in S. alfredii soil experienced a considerable rise. After being inoculated with AMF, two hyperaccumulators preferentially recruit Pseudomonas, a microbe that is also a particular flora involved in the geochemical cycle of soil phosphorus. Massilia, Sphingomonas and Nocardioides may be metal-tolerant bacteria enriched by hyperaccumulators under heavy metal stress. Following AMF colonization, both hyperaccumulating plants selectively enriched Pseudomonas and Streptomyces species. Upon AMF inoculation, the relative abundance of Cd-and P-related genes increased in the rhizospheric soil of S. nigrum and S. alfredii, focusing on phosphorus cycling genes, S. nigrum mainly emphasized organic phosphate mineralization gene while S. alfredii mainly emphasized phosphorus transport genes. AMF encouraged the recruitment of microbial communities linked with Cd and P transport, mineralization function, and basic ecological functions differed in microbial recruitment between stonecrop and mustard. These microorganisms, which carry genes encoding various phosphorus cycling and cadmium-related genes, were recruited in the rhizosphere soil of hyperaccumulator-AMF symbionts following AMF colonization. This suggests that they may improve soil phosphorus cycling and increase hyperaccumulators' uptake of cadmium. These results provide insights into new ways for microorganisms to improve phytoremediation of metal-contaminated soils by indicating that hyperaccumulators selectively recruit phosphorus and cadmium-related microorganisms to improve the acquisition of nutrients and cadmium by hyperaccumulators during AMF inoculation.