Harnessing mycorrhizal flexibility enhances soil nitrogen acquisition and productivity in Eucalyptus plantations

Eucalyptus is a fast-growing plantation tree species cultivated worldwide and is a typically dual-mycorrhizal tree. Dual-mycorrhizal Eucalyptus provides a valuable model to investigate how mycorrhizal associations influence soil nutrient acquisition, which could account for its success in afforestation. However, the relationships between dual-mycorrhizal associations and soil nitrogen (N) acquisition, as well as plant growth in Eucalyptus , remain poorly understood. This study examined the dynamics of mycorrhizal switching and soil N preference in a dual arbuscular mycorrhizal/ectomycorrhizal (AM/ECM) Eucalyptus across a stand chronosequence of 2–22 years. We then conducted a pot experiment to evaluate the responses of mycorrhizal 15 N uptake and growth of Eucalyptus respond to separate or combined inoculation with AM fungi and ECM fungi. The results indicated a significant shift from AM to ECM dominance in dual-mycorrhizal Eucalyptus as stand age increased. AM fungi and ECM fungi exhibited distinct soil N preferences: compared with ECM associations, AM associations showed positive correlations with inorganic ammonium and organic N, while displaying negative correlations with soil nitrate. Dual inoculation with AM and ECM fungi synergistically enhances Eucalyptus growth and 15 N uptake relative to single inoculation. The observed benefits of dual-mycorrhizal associations were consistent with complementary nutrient acquisition strategies between different AM and ECM fungi species. In contrast to AM associations, ECM associations demonstrated both direct and indirect positive effects on Eucalyptus foliar N content and growth, potentially mediated by microbial N cycling genes. This study highlights the ecological significance of mycorrhizal switching in optimizing soil N acquisition and suggests implications for afforestation productivity. These findings underscore the role of dual-mycorrhizal associations in supporting flexible nutrient-use strategies, which may promote Eucalyptus growth in nutrient-poor soils and contribute to sustainable forest management.