Boosting plant welfare and rhizospheric health through the application of phosphorus and potassium-solubilizing fungi from compost and vermicompost

The overuse of agrochemicals has led to soil nutrient depletion and loss of microbial diversity, threatening sustainable crop production. As a sustainable and environmentally friendly alternative, the use of plant growth-promoting microorganisms (PGPMs) can enhance nutrient uptake and overall crop health. In particular, phosphorus (P) and potassium (K) are essential macronutrients that significantly contribute to crop growth and development. Given that certain microorganisms can enhance the availability of these nutrients by solubilizing their insoluble forms, exploring beneficial microbes from compost and vermicompost presents a promising sustainable strategy. Therefore, the main objective of this work was to isolate phosphate- and potassium-mobilizing microorganisms from compost and vermicompost samples and to evaluate their combined application with P-K rich agrochemicals in order to optimize nutrient assimilation during the early developmental stages of tomato plants. A total of 50 morphologically distinct microbial strains were isolated from the composts, including 36 P-solubilizing strains (2 fungi and 34 bacteria) and 14 K-solubilizing strains (3 fungi and 11 bacteria). The strains that showed the highest in vitro solubilization capacity were identified and tested as plant promoting agents in tomato seedlings. In addition, the P-K uptake by seedlings was evaluated as a function of different biofertilization strategies. The fungal strains tested, Penicillium chrysogenum PH2 (P solubilizer) and Aspergillus costaricensis KH2 (K solubilizer), showed the most notable beneficial effect on the improvement of basic plant growth parameters. Moreover, the combined fertilization strategy was found to improve nutrient uptake and the abundance of solubilizing microbial communities present in the rhizosphere.