Comparative evaluation of eggshells wastes and tricalcium phosphate as substrates for phosphate and calcium solubilization by arid ecosystem fungal isolates

Abstract Fungi can solubilize tricalcium phosphate and eggshell-derived calcium, thereby accelerating nutrient availability and supporting their sustainable use as biofertilizers. This study investigated the solubilization efficiency of four fungal isolates named, Aspergillus terreus (26L), Aspergillus fumigatus [(7L), Emericella nidulans var cristata (1Fcit) and Asperagillus flavus (4Fcit) as using eggshells (EgSh) and tricalcium phosphate (CPh) as growth media substrates, with emphasis on pH reduction, phosphate, and calcium release. All isolates significantly decreased medium pH, with the strongest acidification recorded for 1Fcit (pH 1.2) and 4Fcit (pH 1.6) on tricalcium phosphate substrate (CPh), while eggshells (EgSh) exhibited more moderate declines due to its carbonate buffering capacity. Phosphate solubilization was higher from CPh, where 26L reached a maximum of 0.26 mg mL⁻ 1 , compared to EgSh, which was the highest at 0.067 mg mL⁻ 1 with 4Fcit fungus. Conversely, calcium release was greater from EgSh, with 4Fcit fungus and 1Fcit fungus reaching 12 and 8.2 mg mL⁻ 1 , respectively, while 26L and 7L fungi were weak Calcium solubilizers. These results demonstrated that fungal activity is closely linked to medium acidification [pH] and that solubilization performance is substrate specific subject, with isolates Aspergillus terreus (26L) and Asperagillus flavus (4Fcit) from ecological view showed the greatest potential as bio- fertilizers.