Role of arbuscular mycorrhizal fungi in cadmium tolerance in rice (Oryza sativa L): a meta-analysis

Rice is an important agricultural product consumed globally. Rice polluted by cadmium (Cd) poses serious health risks. Numerous studies have shown that arbuscular mycorrhizal fungi (AMF) decrease Cd concentrations in the grain, shoots, and roots of rice. However, one study showed that AMF increased the root Cd concentration in rice. Therefore, a meta-analysis of the contribution of AMF to rice Cd tolerance became necessary. This meta-analysis was conducted to analyze the role of AMF in Cd tolerance in rice by searching the following databases: ProQuest, PubMed, Scopus, and ScienceDirect. A total of 571 studies were found, of which nine studies and 25 datasets were used in the meta-analysis. The period of inclusion of research reports was from January 1992 to April 2022. The results showed that with the addition of Rhizophagus irregularis, Cd concentration in the roots was higher than in the control group, although the overall Cd concentration in the plant was reduced. Four species of AMF reduced Cd concentration in rice shoots and grain tissues. These AMF species increased the biomass of rice root and shoot tissues; however, they did not affect grain biomass. AMF decreased the transfer factor (TF), and the TF of Glomus versiforme (12.99%) was significantly lower than the other three AMF types. We proposed that Cd could be enriched in rice roots, and the transfer of Cd to the grain could be inhibited. At the time of grain harvesting, rice roots are removed from the soil, thus removing Cd from the soil. This operation can efficiently improve both land-bearing capacity and soil without affecting rice yield. Thus, Cd was enriched in rice roots, and the poten-tial for Cd transfer to the grain was inhibited due to the decreased TF. The future research must focus on how R. irregularis could improve the HMA3 gene expression in rice root, and prevents the transportation of Cd from the roots to shoots.