Phytohormone-producing fungal endophytes and hardwood-derived biochar interact to ameliorate heavy metal stress in soybeans

This study identifies the potential use of the combined application of hardwood-derived biochar (BC) and phytohormone-producing endophytes for enhancing crop production under heavy metal stress. For this purpose, the endophyte Galactomyces geotrichum WLL1 was isolated from Trapa japonica inhabiting a Korean river whose rainfall catchment area included an abandoned zinc mine. Pyrolyzed BC derived from pine hardwoods was obtained commercially. Under growth chamber conditions, the combined or individual application of G. geotrichum WLL1 and BC (15 % w/w) significantly improved soybean growth with or without excess Zn (5,253.6 mg kg⁻¹). The beneficial effect of treatments was observed in the low uptake of Zn by different plant tissues and its immobilization in the soil. Biochar and G. geotrichum WLL1 shared their beneficial properties synergistically and improved plant growth characteristics with or without Zn heavy metal stress (HMS). Further, intensive root colonization of G. geotrichum WLL1 in the presence of BC was observed irrespective of HMS. Most interestingly, BC and G. geotrichum WLL1 had a priming effect by inducing systemic resistance in soybeans as revealed by significantly large amounts of jasmonic acid. These properties of BC could be exploited under abiotic and biotic stress. Here, for the first time, the combined application of hardwood-derived BC and phytohormone-producing endophytes is recommended for environmentally friendly and cost-effective crop production under HMS.