Differential effects of arbuscular mycorrhizal fungi on three salt-tolerant grasses under cadmium and salt stress

Salt-tolerant plants generally grow in salty conditions, and some of them are also tolerant to heavy metal stress. Arbuscular mycorrhizal fungi (AMF) can help plants withstand abiotic stresses. However, few studies have focused on the effects of AMF on the growth of salt-tolerant plants in cadmium (Cd)-contaminated saline soils. In this study, a greenhouse pot experiment was conducted to investigate the effects of AMF (Funneliformis mosseae) on growth, ion uptake, and Na+ and Cd translocation in three salt-tolerant grasses (Leymus chinensis, Puccinellia distans, and Astragalus adsurgens) in a Cd-contaminated saline soil. The regulation of genes by AMF in A. adsurgens was also explored by transcriptome analysis. The results showed that AMF increased the biomass of A. adsurgens but not that of L. chinensis and P. distans. AMF promoted phosphorus (P) uptake from soil and improved shoot K+: Na+ ratio, but it decreased shoot Na+ and Cd concentrations and their translocation rates in A. adsurgens. Transcriptome analysis showed that AMF upregulated the differentially expressed genes (DEGs) encoding cytokinins, which may be linked to the increase in shoot biomass in inoculated A. adsurgens, but downregulated the DEGs related to light harvest, suggesting avoidance of photodamage. AMF downregulated the DEGs in the pathways of the cell wall and those associated with antioxidant enzymes. These results suggest that AMF symbiosis in A. adsurgens effectively alleviates the Na+ and Cd toxicity of shoots. This study implies the potential to use salt-tolerant grasses in association with AMF to rehabilitate the heavy metal-contaminated saline ecosystems.