Ectomycorrhizal fungi and dark septate endophyte inoculation improve growth and tolerance of Pinus tabulaeformis under cadmium stress

Forest trees can establish symbiotic associations with dark septate endophytes (DSEs) and ectomycorrhizal fungi (ECMF) simultaneously. However, the combined effects of these two fungi on the growth and cadmium (Cd) tolerance of host plants remain largely unexplored. To address this knowledge gap, a pot experiment was conducted to examine the impact of the interaction between ECMF (Suillus granulatus) and DSEs (Pseudopyrenochaeta sp.) on Pinus tabulaeformis under Cd stress. Various growth and physiological indicators, nutrient uptake, and soil properties were assessed to evaluate the impact of the fungal strains. Notably, the colonization rates of both fungal strains were found to increase in response to Cd stress, with the extent of this increase being influenced by the specific fungal species and the level of Cd in the soil. Compared to the uninoculated treatment, single inoculation of P. tabulaeformis seedlings resulted in enhanced biomass, root development, and nutrient contents under Cd stress conditions. Furthermore, a synergistic effect was observed when these seedlings were simultaneously infected with S. granulatus and Pseudopyrenochaeta sp., as indicated by significantly greater measurements in various indicators compared to both the single-inoculated and uninoculated treatments. Fungal inoculation effectively regulated the antioxidant defense responses and photosynthesis of P. tabulaeformis seedlings subjected to excess Cd stress, particularly under mixed inoculation conditions. In addition, the fungal inoculation facilitated the accumulation of Cd in P. tabulaeformis, suggesting a promising potential for the implementation of bioremediation strategies in areas contaminated with heavy metals. The findings from this study indicate that the utilization of root symbiotic fungi obtained from stressed environments could potentially enhance the growth performance and tolerance of P. tabulaeformis towards heavy metals, and simultaneous inoculation of both fungal groups may result in even more pronounced synergistic effects on the overall fitness of the plant.