Cultivar and tree age jointly shape rhizosphere bacterial diversity and community assembly in Macadamia integrifolia

This study investigates the regulatory effects of cultivar and tree age on the rhizosphere bacterial community of Macadamia integrifolia, aiming to provide theoretical support for targeted regulation of the rhizosphere microecosystem and high-quality, high-yield production in the industry. Using rhizosphere soil from 5-year-old and 8-year-old plants of five major cultivated cultivars as materials, the bacterial community characteristics were revealed through 16S rRNA gene high-throughput sequencing combined with R-based data analysis and visualization. The results show that the community is dominated by two phyla, Actinobacteria and Chloroflexi, with the core dominant genus being Rhodoplanes. Cultivar is the leading factor driving community differentiation, and the effect of tree age is cultivar-specific. Functionally, the community is dominated by amino acid, carbohydrate, and lipid metabolic pathways, which are well-adapted to the host plant's growth demands; the co-occurrence network exhibits predominantly strong positive correlations and high modularity, suggesting synergistic adaptation and metabolic complementarity among dominant bacterial taxa. This study clarified that the rhizosphere bacterial community of Macadamia integrifolia is primarily regulated by cultivar, and has identified core functional taxa such as Rhodoplanes, laying a scientific foundation for the development of specialized microbial inoculants and the coordinated regulation of cultivar-microbe interactions. KEY POINTS: • Cultivar is the dominant driver of macadamia rhizosphere bacterial community, with tree age exerting cultivar-specific effects. • Rhodoplanes is the core dominant genus, and the bacterial community functions are dominated by metabolic pathways. • Macadamia rhizosphere bacterial co-occurrence network shows strong positive correlations and modularity, guiding microbial inoculant development.