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Role of rhizosphere bacteria and root exudates on the assimilation of phosphorus




Pantigoso Guevara, Hugo A., author
Vivanco, Jorge M., advisor
Fonte, Steven, committee member
Davis, Jessica, committee member
Manter, Daniel, committee member

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Deficient phosphorus (P) bioavailability in soils is a major challenge for sustainable food production as effective strategies to access unavailable P are limited. Solubilizing-bacteria and root exudate metabolites that solubilize P are promising approaches to increase available P for plants. We hypothesized that compounds in root exudates could elicit the P-solubilization activity of bacteria. To test this hypothesis, the root exudates of Arabidopsis grown in vitro under sufficient and deficient P conditions were characterized using GC-MS. We tested the ability of previously screened root exudates to solubilize plant-unavailable P in vitro. In parallel, potential P-solubilizing bacteria were isolated from the rhizosphere of wild potatoes using conventional microbiology techniques. The bacteria strains were tested, both individually and in consortia, for their ability to solubilize organic (phytin) and inorganic (calcium) P sources in vitro and in planta. Lastly, selected root exudate compounds were incubated together with P-solubilizing bacteria, and bacterial growth, P solubilization activity, and plant growth were evaluated. Our results demonstrate that malic, nicotinic, and 3-hydroxypropionic acids improved solubilization of P as compared to a control. Likewise, the bacterial strains E. cloacae, P. pseudoalcaligenes, and B. thuringiensis enhanced plant growth and P content with additions of plant-unavailable P. Furthermore, we found that threonine and 4-hydroxybutyric acid elicit P solubilization in all bacteria, under both organic and inorganic sources, independent of bacterial growth. Subsequent exogenous application of threonine to soils improved plant root growth, enhanced nitrogen and phosphorus content in roots and increased available levels of potassium, calcium, and magnesium in soils. Altogether, our findings expand on the function of exuded specialized compounds and suggest approaches to effectively recover residual P from soil, improving crop growth and nutrition.


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root exudates


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