Abstract: Using untargeted metabolomic and high-throughput sequencing technique, we investigated the differences in root exudates of Juglans mandshurica between J. mandshurica pure plantation and Larix gmelinii-J. mandshurica mixed plantation, with KEGG functional annotation and enrichment analysis. We examined the characteristics, functions, and keystone species network structure of the rhizosphere microbial community, as well as the relationship between root exudates and microorganisms. The results showed that a total of 181 metabolites were identified in the root exudates of J. mandshurica, with significant differences between pure and mixed plantations. There were 105 types from pure plantation. Compared with the mixed plantation, compounds like indolephenanthridine and S-adenosylhomocysteine showed higher relative abundances in pure plantation, and pathways such as atrazine degradation and cyclic nucleotide signaling were more enriched. The mixed plantation contained 76 species of meta-bolites. Compared with the pure plantation, compounds like lavendustin C and benzyl glucosinolate showed higher relative abundances, and pathways including biotin metabolism and phenylalanine degradation were more enriched. In the mixed plantation, L. gmelinii significantly reduced the Ace index (16.2%) and the Chao1 index (16.2%) of fungal community in rhizosphere soil of J. mandshurica, increased the relative abundances of the fungal phyla Mortierellomycota (33.7%), Basidiomycota (39.6%), and Rozellomycota (69.3%), as well as the bacterial phylum Myxococcota (58.8%), and increased the relative abundances of the endophytic fungal groups and the nitrate-reducing bacterial groups by 35.5% and 102.1% in the rhizosphere soil. The redundancy analysis revealed that benzamide compounds and 3-(acrylic acid)-o-benzoquinone were the key factors significantly influencing the composition of rhizosphere fungal community. The independent contribution of sphingolipid substances to bacterial community structure reached 41.7%. After mixed with L. gmelinii, J. mandshurica could alter its root exudate composition, reshape the rhizosphere microbial community, form a functionally enriched structure, and drive the metabolic pathways towards biotin metabolism, phenylalanine degradation and other nutrient cycling directions.

Key words: mixed plantation, root exudate, rhizosphere microorganism, untargeted metabolomic, high-throughput sequencing