Rhizosphere microbiome-related changes in soil zinc and phosphorus availability improve grain zinc concentration of wheat

Background Zinc (Zn) enrichment in cereal grains is a promising method to relieve human Zn malnutrition. Many factors influence grain Zn accumulation, but the role of rhizosphere microbes in soil environment and crop Zn uptake remain unknown. Methods This study examined the relationships between rhizosphere microbes, rhizosphere soil nutrients, vegetal and grain Zn concentrations in six wheat ( Triticum aestivum L.) cultivars with contrasting grain Zn concentrations grown in Zn-deficient soil. Results Roots and spikes Zn concentrations at anthesis were positively correlated with grain Zn concentrations. Root Zn concentration was negatively correlated with rhizosphere soil available phosphorus (AP) and Zn (AZn). Spike Zn concentration was positively correlated with rhizosphere ammonium-N. The bacterial community assembly was more profoundly dominated by stochastic processes in the rhizosphere of high-Zn cultivars. Specifically enriched microbes were found within 144 amplicon sequence variants (ASVs) affiliated with 15 phyla in the rhizosphere of the high-Zn cultivars at anthesis. Enriched microbes significantly correlated with AZn were only identified in the rhizosphere of high-Zn cultivars, where g_Olivibacter and o_Microtrichales had the function of decomposing organic matter, potentially facilitating the formation of organic acids and dissolving soil Zn. The AP-related enriched microbes g_Lysobacter , g_Crossiella , and g_TM7a in the rhizosphere of high-Zn cultivars were significantly negatively correlated with AP, indicating their role in decreasing the AP. Conclusion This study implied that the rhizospheric microbes in the high-Zn cultivars had the potential function of increasing soil Zn availability and decreasing soil P availability, as an important microbial strategy for wheat grain Zn biofortification.