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Document Type

Dissertation - University Access Only

Award Date

1992

Degree Name

Doctor of Philosophy (PhD)

Department / School

Plant Science

First Advisor

T.E. Schumacher

Abstract

The rhizosphere (soil-root interface) is the unavoidable link in the transfer of nutrients from soil to plant. There are no published studies, however, of rhizosphere physicochemical properties and nutrient solubility for maize genotypes. Progress in this field is restricted by a lack of convenient methods to examine this opaque and structurally complex medium without disturbing the soil-root interface. This study was 1 conducted to: (1) fabricate a pCO2 microelectrode that would permit analysis of small samples and withstand insertion into the soil; (2) evaluate the suitability of an aseptic agar technique for determining the ability of plants to induce pH change in the rhizosphere and characterize pH patterns within the root system; and (3) determine the effect of bulk soil CaCO3 level on rhizosphere properties and whether the rhizosphere physicochemical properties of two maize cultivars are different. A pCO2 microelectrode was developed by making use of a newly developed pH microelectrode and a semiliquid chlorotrifluoroethylene gas permeable membrane. The fabricated microelectrode had a tip diameter of < 120 µm and a response time of < 3 minutes with a linear slope (58.0 ± 2 mV /log10 pCO2). The ability of the 2 embedded roots to induce pH changes in an aseptic agar medium was followed by photographing the color change of an indicator. The pH at different root zones (maturation, elongation and meristematic) was also monitored by a pH microelectrode. The agar method allows the determination of a cultivar's capability to induce rhizosphere pH changes, while the microelectrode method is necessary for quantifying the spatial variation of specific root developmental zones with high resolution. Soluble nutrients within the rhizosphere (1-, 2- and 3-mm distances from the root surface) of maize (Zea mays L., cv., Pioneer-3732 and -3737) were determined. The roots of the two maize genotypes altered the nutrient composition within the rhizosphere and responded differently to the CaC03 content of the bulk soil. In the calcareous soil, the plant K+/(Ca2+ + Mg2+) ratios were reduced to 47% and 78% for Pioneer-3732 and -3737 respectively, compared to those in the noncalcareous soil. The difference in K+ uptake between the two cultivars was related to differences in rhizosphere pH and pCO2 as well as differences in Ca2+ and Mg2+ uptake.

Library of Congress Subject Headings

Rhizosphere
Plant-soil relationships
Plants -- Nutrition

Format

application/pdf

Publisher

South Dakota State University

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