关键词: 蒙古栎, 根际土壤, 非根际土壤, 微生物群落结构, 土壤碳氮耦合

Abstract

Aims: The rhizosphere is a critical interface for plant–soil interactions, shapes forest soil nutrient cycling through the differentiation between rhizosphere and non-rhizosphere microbial community structures and their regulatory roles in carbon (C) and nitrogen (N) dynamics. This study aimed to characterize the structural and functional differences of microbial communities in rhizosphere and non-rhizosphere soils of Quercus mongolica pure forests, and to elucidate their responses to soil C and N gradients. 

Methods: Soil samples were collected from rhizosphere (R) and non-rhizosphere (NR) soils of Quercus mongolica pure forests in eastern Liaoning, China. Bacterial 16S rRNA and fungal ITS regions were sequenced, and amplicon sequence variants (ASVs) were clustered with 97% similarity. α diversity indices (Shannon diversity index, Simpson diversity index, Chao1 richness index, Pielou evenness index) and β diversity (NMDS analysis based on Bray-Curtis distance and PERMANOVA test) were analyzed to assess microbial community species richness and heterogeneity. Microbial functions were were predicted using PICRUSt2 based on the MetaCyc database. Soil total carbon (TC), total nitrogen (TN), soil organic carbon (SOC), and C : N were measured using standard protocols. Mantel tests and Pearson correlations were used to evaluate linkages between microbial communities and soil carbon and nitrogen content.

Results: The number of unique ASVs was higher in the rhizosphere soil than in the non-rhizosphere soil. At the phylum level, rhizosphere bacterial communities were dominated by Proteobacteria and Acidobacteria. In the fungal community, the abundance of Ascomycota was significantly higher in the rhizosphere than in the non-rhizosphere, whereas Basidiomycota showed the opposite trend. Copiotrophic bacteria prevailed in the rhizosphere by rapidly utilizing simple carbon sources derived from root exudates, while oligotrophic taxa in the non-rhizosphere were adapted to the nutrient-poor conditions. The predominance of Ascomycota in the rhizosphere and Basidiomycota in the non-rhizosphere was mainly driven by heterogeneity between the rhizosphere effect (characterized by carbon input) and the non-rhizosphere environment (involving decomposition of organic matter). α diversity analysis showed that the Shannon diversity index and Chao1 richness index of fungal communities were significantly higher in the rhizosphere than in the non-rhizosphere, while no significant difference was observed in bacterial diversity. β diversity analysis indicated significant differences in microbial community composition between the rhizosphere and non-rhizosphere soils. Functional prediction suggested that bacterial and fungal communities in Quercus mongolica forest soils were enriched in metabolic pathways related to amino acid biosynthesis and respiration, respectively. Their complementary metabolic functions—such as cofactor synthesis and carbon-nitrogen exchange—may enhance the efficiency of nutrient cycling in these forest soils. Rhizosphere soils were enriched with organic matter-degrading bacteria (such as Candidatus udaeobacter) and nitrogen-cycling functional bacteria (such as Bradyrhizobium), whose metabolic pathways may be dominated by amino acid biosynthesis. Soil carbon and nitrogen gradients had an impact on microbial diversity and abundance through resource competition and metabolic adaptation: rhizosphere bacterial diversity was positively correlated with organic carbon, and fungal community abundance was significantly correlated with total carbon and C : N. 

Conclusion: Quercus mongolica rhizosphere effects drive microbial community assembly through resource competition and metabolic adaptation, fostering copiotrophic bacteria and symbiotic fungi that enhance nutrient acquisition. The strong coupling between microbial diversity and soil carbon and nitrogen gradients highlights the ecological significance of rhizosphere microbiomes in regulating forest soil fertility. These findings provide a mechanistic basis for leveraging rhizosphere engineering in the sustainable management and ecological restoration of degraded Q. mongolica forests in northeastern China.

Key words: Quercus mongolica, rhizosphere soil, non-rhizosphere soil, microbial community structure, soil carbon and nitrogen coupling