Crop growth is increased by arbuscular mycorrhizae for both phosphate rock and soluble phosphorus fertilizers, but fertilizer solubility primarily determines crop growth

Arbuscular mycorrhizae (AM) are thought to improve crop growth by enhancing phosphorus (P) uptake via scavenging and enhancing dissolution. However, AM-mediated crop growth responses to P forms of varying solubility are often crop-species and soil-context dependent. The relative importance of AM associations and P source solubility on crop growth is not conclusively understood, and requires controlled factorial experiments to test their relative and interactive effects. We conducted a meta-analysis to evaluate how AM impact crop growth responses to rock phosphate relative to soluble phosphates across diverse crop species and soil characteristics. A total of 83 observations utilizing a 2 × 2 factorial design of relative presence or absence of AM and fertilization with rock phosphate vs. soluble phosphates were identified. We found that AM similarly improved crop growth with rock phosphate and soluble phosphates. A distinguishable crop growth benefit from AM coupled with rock phosphate was observed for soils with a low degree of weathering, at soil pH < 6.5 and > 7.5, and when soils were heat-sterilized prior to inoculation with AM. Shoot biomass of legumes was uniquely greater than non-legumes with rock phosphates and AM as compared to soluble phosphates and AM. However, crop growth under rock phosphate fertilization relative to soluble phosphates was still lower irrespective of AM. This meta-analysis reveals that crop growth is more dependent on P fertilizer solubility than AM. Moreover, AM do not appear to close the solubility gap of rock phosphate vs. soluble phosphate fertilizers to support similar crop growth under rock phosphate relative to soluble phosphates. Studies assessing crop growth responses to AM-crop associations effect on contrasting solubility P fertilizers should expand to the field, and greenhouse experiments should be conducted under realistic field growing conditions, such as agronomically appropriate P application rates.