To investigate the growth-promoting effects of ectomycorrhizal fungus-Lactarius deliciosus on Pinus taeda seedlings.

Six-month-old Pinus taeda seedlings were used as the research material, in a constant temperature and humidity light culture environment, the seedlings were inoculated with L. deliciosus solid inoculum and an infection experiment was conducted for a period of two months. A pot-controlled experiment was adopted to evaluate the mycorrhizal colonization rate, growth volume, chlorophyll content of coniferous leaves, changes in antioxidant enzyme activities and malondialdehyde (MDA) content systematically. Subsequently, the changes and enrichment of differentially expressed genes (DEGs) in the transcriptome was analyzed.

L. deliciosus establish a successful symbiotic relationship with Pinus taeda seedlings, exhibiting a strong mycorrhizal effect with a mycorrhization rate reaching 64.29%. Compared to the non-inoculated control group (CK), inoculation with L. deliciosus significantly enhanced seedling growth; the height and ground diameter of mycorrhizal seedlings increased by 29.18% and 20.65%, respectively. Total chlorophyll content increased by 30.85%. Activities of the antioxidant enzymes peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD) were enhanced by 43.70%, 61.52% and 37.40%, respectively. Analysis based on transcriptome data showed that differentially expressed genes (DEGs) were significantly enriched in the pathways of phytohormone signal transduction, starch and sucrose metabolism, and phenylpropanoid biosynthesis.

Mycorrhization significantly improved photosynthetic capacity and oxidative stress resistance, ectomycorrhizae may promote seedling growth by modulating hormone signaling networks and secondary metabolic pathways.