Rhizophagus irregularis combined with biochar can improve the saline-alkali tolerance and energy quality of switchgrass through osmoregulation and gene expression

Arbuscular mycorrhizal fungi (AMF) and biochar have potential applications in agriculture and ecological restoration. However, the effects of AMF combined with biochar on the bioenergy quality of plants under saline-alkali stress have not been thoroughly studied. In this study, we examined the effects of Rhizophagus irregularis (Ri) and biochar application, individually or in combination, on the growth, osmoregulation, ion uptake, and expression of energy quality-related genes in switchgrass under saline-alkali stress. The results showed: (1) The biomass of switchgrass in the BR treatment group increased by 35.50 % and 39.71 % compared with the BC and Ri treatment groups, respectively; (2) Ri combined with biochar increased the activity of antioxidant enzymes and the accumulation of osmoregulatory substances, and influenced plant hormone synthesis; (3) The combined treatment significantly increased the contents of K+, Ca2+, and Mg2+ in leaves and roots, reduced the contents of Na+, and maintained high K+/Na+, Ca2+/Na+, and Mg2+/Na+ ratios; (4) The expression levels of stress response, reactive oxygen scavenging, ion transport, and cellulose biosynthesis genes in leaves and roots of switchgrass were the highest in the BR treatment; (5) The cellulose, hemicellulose, and calorific value of switchgrass in the BR treatment group reached maximum values of 29.2 %, 29.1 %, and 17.6 MJ/kg, respectively. Our findings demonstrate that Ri combined with biochar can enhance the saline-alkali tolerance of switchgrass, improve plant energy quality, and provide a new approach for increasing the planting area and improving the quality of energy plants.