Application of Biofertilizers as a Strategy to Reduce P-Mineral Fertilization in the Production of Eucalyptus globulus Labill.

Eucalyptus (Eucalyptus globulus Labill.) plays a fundamental role in the Portuguese forestry sector, highlighting the need for sustainable practices that contribute to maintain soil fertility and biodiversity, without compromising productivity. An experiment was conducted, with a low extractable-P soil (<10 mg P₂O₅ kg⁻¹), to evaluate the use of biofertilizers as a strategy to reduce mineral fertilizers dependency. Eucalyptus trees were inoculated at transplantation, with two commercial inoculants based on Glomus iranicum (an arbuscular mycorrhizal fungus, AMF) and inorganic phosphate-solubilizing bacteria (Pseudomonas putida and Pseudomonas fluorescens), under differential P fertilization conditions. Reducing P fertilization to 70% and 40% of the reference dose did not significantly reduce final aboveground biomass, under the studied conditions. Biofertilizer application enhanced soil P availability, particularly when AMF and Pseudomonas were co-inoculated, suggesting synergistic effects on P mobilization and uptake. Plant physiological performance, assessed through vegetation indices, remained stable across treatments, indicating effective acclimation to reduced P supply, while stomatal conductance suggested improved tolerance to P deficiency in Pseudomonas-inoculated plants. The widespread presence of a well-established native mycorrhizal community, which led to a higher root colonization under low P conditions, highlights the importance of plant–microbe interactions in nutrient-limited environments. Overall, these findings underscore the potential of integrating reduced P fertilization with microbial inoculants to improve P use efficiency and support sustainable eucalyptus production.