Beneficial fungi reprogram tree metabolism toward growth and stress-associated pathways

Beneficial fungi are increasingly recognized as key modulators of plant growth and stress resilience, yet their functional roles in woody tree species remain poorly understood. Here, we examined the physiological, nutritional, and metabolic responses of sengon (Falcataria moluccana) to two plant growth-promoting fungi, Penicillium olsonii TLL1 and Aspergillus aculeatus TLL1, during a 6-month greenhouse experiment. Inoculation with A. aculeatus significantly enhanced leaf number, and shoot and root biomass compared with uninoculated controls, whereas P. olsonii showed more limited growth effects. Fungal inoculation led to a marked increase in root nutrient accumulation, including nitrogen (~2.5-fold), phosphorus (~1.5-fold), magnesium (~1.75-fold), and zinc (~2.5-fold), relative to controls, indicating improved nutrient acquisition. Untargeted metabolomic profiling revealed extensive metabolic reprogramming, with over 1,600 metabolites detected in negative ion mode and 2,800 metabolites in positive ion mode. Comparative analysis identified 367 and 206 differentially regulated metabolites in P. olsonii- and A. aculeatus-treated plants, respectively. Notably, enhanced nutrient status was accompanied by coordinated shifts in hormone-associated and secondary metabolic pathways, including phenylpropanoid-, lignin-, and terpenoid-related metabolites, consistent with a defense-primed metabolic state rather than constitutive defense activation. Together, these findings demonstrate that beneficial fungi reprogram tree metabolism by coupling improved nutrient acquisition with metabolic allocation toward growth and inducible defense, highlighting their potential role in sustainable forestry systems with tangible yield benefits.