A group from Department of Horticulture and Landscape Architecture, Center for Root and Rhizosphere Biology, Colorado State University, Fort Collins, CO USA, etc. has reported that root exudate compounds (galactinol, threonine, and 4-hydroxybutyric acid) induced under low P conditions can stimulate the ability of bacteria to solubilize P.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10006420/
The effect of the three root-exudate derived compounds on the enhancement of P solubilization by bacteria was assessed.
In the calcium phosphate (inorganic) media, threonine, 4-hydroxybutyric acid, galactinol, and the combination of compounds significantly increased dissolved P in the medium for Enterobacter cloacae and Pseudomonas pseudoalcaligenes. For Bacillus thuringiensis, only threonine and 4-hydroxybutyric acid increased dissolved P.
In phytin (organic phosphate) media, the effect of the compound additions on the enhancement of P solubilization was not significant for any of the bacterial strains.