Eight bacterial strains expressing high-levels of rock phosphate solubilization were isolated from Tunisian agricultural soils. 16S rDNA sequencing assigned these strains to four genera, Pseudomonas, Bacillus, Serratia, and Burkholderia. Both qualitative and quantitative assays were performed to study their plant-growth promoting abilities. Five strains released inorganic phosphorus up to 600 µg ml⁻¹ with rock phosphate as sole phosphorus source. They displayed additional capabilities of producing phytases (16.1–24.8 Uml⁻¹), IAA (till 39.6 µg ml⁻¹) and siderophores (9–81.1%). When tested on Medicago truncatula on sterile stand, two strains were discarded since they did not show significant enhancement. The remaining bacterial strains, Pseudomonas corrugata SP77, Pseudomonas koreensis LT62, and Pseudomonas frederiksbergensis G62, were further tested on Medicago in two phosphorus-deficient soils amended with Tunisian rock phosphate. The three strains induced significant enhancement in shoot dry weight and nodule fresh weight; however, the best results were observed with SP77 and the consortium. The increase in shoot dry yield ranged from 40 to 134% and from 13 to 87% for soil 1 and soil 2, respectively. The biomineralization of rock phosphates by these elite strains will constitute an eco-friendly alternative to chemical fertilizer, mainly in neutral and alkaline soils.

The objective of this study is to evaluate the impacts of the direct use of natural rock phosphates on two forage legumes, Vicia sativa, and Medicago sativa. Crops were grown in pots containing two P deficient soils and fertilized with Tunisian rock phosphate (TRP) or chemical triple superphosphate (TSP). TRP amendment significantly increased shoot dry yield (+53% to +162%), P-content, protein content, and chlorophyll content mainly at the rate of 150 kg P ha⁻¹. No significant effects were observed on mycorrhization and antioxidant enzyme activities. However, TSP negatively affected the frequency of root mycorrhization and stimulated antioxidant enzyme activities. TRP amendment induced an increase in fluorescein diacetate activity, alkaline phosphatase activity, and species richness. The stimulation involved mainly Actinobacteria, Proteobacteria, and Firmicutes with higher stimulation of Actinobacteria in the case of vetch. The present work indicated a better P-use efficiency of vetch. It suggested also that at least a part of the enhancement observed in plant-growth parameters following TRP fertilization is driven by changes in the structure of rhizosphere microbial communities. Nevertheless, the correlation between changes in microbial composition and phosphorus uses efficiency needs to be investigated further.

Protists represent a major component of eukaryotic diversity within the soil microbiome, playing critical roles in mediating carbon and nitrogen cycling and influencing nutrient availability and soil health. Their diversity is shaped by multiple factors, including temperature, pH, organic matter content, and land use. In this study, we investigated the protist diversity in rhizosphere soils from both wild and cultivated date palm varieties. Our results identified nitrate, nitrite, calcium, and carbon content as key soil factors significantly correlated with protist diversity. Only 9.2% (42) of operational taxonomic units (OTUs) were shared across all soil samples, suggesting that these taxa possess traits enabling adaptation to extreme environmental conditions. The dominant protist families belonged to Rhizaria, Alveolata, Amoebozoa, and Archaeplastida, primarily comprising bacterial consumers, alongside taxa from Stramenopiles, Opisthokonta, Hacrobia, and Excavata. At the class level, Filosa-Sarcomonadea, Colpodea, Variosea, Tubulinea, and Chlorophyceae were the most abundant. Filosa-Sarcomonadea and Colpodea were positively correlated with bacterial and fungal genera, suggesting their role as consumers, while Variosea showed a negative correlation with bacteria, reflecting predator-prey dynamics. Notably, the protist community composition in wild date palm rhizosphere soils was distinct from that in cultivated soils, with Opisthokonta being particularly abundant, likely reflecting adaptation to drought conditions. Overall, this study highlights the significant differences in protist diversity and community structure between wild and cultivated date palm ecosystems.