Unlocking soil phosphorus resources in semi-arid regions using arbuscular mycorrhizal fungi and phosphorus solubilising bacteria: a systematic review

Semi-arid regions are generally alkaline and deficient in nutrients, specifically phosphorus (P), due to extremely dry climates. In such soils, integrating phosphate-solubilising bacteria (PSB) and arbuscular mycorrhizal fungi (AMF) can provide a synergistic effect that will unlock fixed P resources, thus promoting nutrient uptake, plant growth, and crop yields. Therefore, this study aimed to review and discuss the role of PSB and AMF on soil fertility, crop growth, and factors affecting their performance in semi-arid regions, consolidate findings from various studies to allow for comparisons across different soils, crops, and microorganisms. Twenty-nine primary studies were selected from various databases based on the inclusion and exclusion criteria of the Preferred Reporting Items for Systematic Reviews and Meta-analyses method. The inoculation of PSB and AMF individually increased available P, plant growth, yield, and P-uptake. However, dual inoculation of PSB and AMF outperformed the application of PSB or AMF alone, suggesting a synergism between these microorganisms in improving plant growth and available P. The lack of response of available P and P uptake to PSB and AMF inoculation in some studies was likely caused by high P-fixation, which was not reported in all the studies. Our study highlights the potential benefits of PSB and AMF inoculation for sustainable agriculture. Initial soil properties, type of plant and microbial strain population were identified as regulatory factors influencing the efficiency of PSB and AMF inoculation. However, future studies should account for P-fixation and fractions when investigating the inoculation effects of PSB and/or AMF to clarify and locate where P is being released.