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dc.creatorJohnson, Sarah Elizabethen_US
dc.descriptionDue to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to, referencing the URI of the item.en_US
dc.descriptionIncludes bibliographical references (leaves 129-134).en_US
dc.descriptionIssued also on microfiche from Lange Micrographics.en_US
dc.description.abstractPhosphate deficiency is frequently a limiting factor in crop production on acid soils due to the tendency of iron oxides to strongly bind phosphate through inner-sphere ligand adsorption. Two of the reported responses of some plants to P-deficiency stress are organic-acid exudation from the roots and increased phosphatase activity. Organic-acid-induced P release from iron-oxide surfaces was studied using synthetic iron oxides. The amounts of P released and Fe dissolved from ferrihydrite and goethite at pH 4.0, 5.5, and 7.0 by citric, malic, melodic, oxalic, succinct, and tartaric acids were measured. At low initial P-adsorption levels, ligand-induced dissolution of the oxide surface as the primary mechanism of P release from oxides was supported by the strong positive relationship between Fe dissolved and P released. At higher initial P-adsorption levels, ligand exchange played a greater role in P release. Ten cultivate of sorghum exhibiting a range of P efficiencies were obtained from EMBRAPA in Brazil and tested for organic-acid exudation and phosphatase activity under P-deficiency stress in hydroponic culture. HPLC analysis of root exudates revealed increases in oxalate and succinate under P- deficient conditions, with significant differences between cultivate. There was no evidence of citrate in the root exudates at either P level. Western blots using arabidopsis purple acid-phosphatase antibodies revealed varying increases in phosphatase activity under P deficiency among the different cultivate. It was concluded that organic-acid exudation might not be expected to significantly improve P uptake by plants grown on weathered soils dominated by well crystalline iron oxide under low P-fertility conditions. Under higher initial P-feritility conditions, organic-acid exudation might play a greater role in plant P acqusitions.en_US
dc.publisherTexas A&M Universityen_US
dc.rightsThis thesis was part of a retrospective digitization project authorized by the Texas A&M University Libraries in 2008. Copyright remains vested with the author(s). It is the user's responsibility to secure permission from the copyright holder(s) for re-use of the work beyond the provision of Fair Use.en_US
dc.subjectsoil science.en_US
dc.subjectMajor soil science.en_US
dc.titlePlant responses to phosphorus-deficiency stress: the role of organic acids in P mobilization from iron oxide and P acquisition by sorghumen_US
dc.typeThesisen_US scienceen_US
dc.format.digitalOriginreformatted digitalen_US

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