Kinetics of Pyro- and Tripolyphosphate Hydrolyses in the Presence of Corn and Soybean Roots as Determined by NMR Spectroscopy
1977
Subbarao, Y. V. | Ellis, R. | Paulsen, G. M. | Paukstelis, J. V.
Kinetics of pyro- and tripolyphosphate hydrolyses by corn (Zea mays L. var. ‘NK P × 50 A’) and soybean (Glycine max L. Merv. var. ‘Cutler 71’) roots were studied using a split-root technique to supply nutrients and to prevent precipitation reactions between phosphate sources and other nutrients. Phosphate species were determined by nuclear magnetic resonance (NMR) spectroscopy after freeze drying to concentrate the sample. A chelating agent eliminated interference by ions in sample solutions. Hydrolyses of pyro- and tripolyphosphates at substrate concentrations of 75 ppm P followed zero-order kinetics. Pyro- and tripolyphosphates were hydrolyzed faster by corn roots than by soybean roots under the conditions studied. The zero-order rate constant for hydrolysis of pyrophosphate was 4.36 × 10⁻² mmoles hour⁻¹ in the presence of corn roots and 1.38 × 10⁻² mmoles hour⁻¹ in the presence of soybean roots. During tripolyphosphate hydrolyses by corn and soybean roots, tripolyphosphate concentration decreased linearly and orthophosphate concentration increased linearly; pyrophosphate hydrolyzed faster than tripolyphosphate. Rate constants for hydrolysis of tripolyphosphate were 2.50 × 10⁻² mmoles hour⁻¹ and 5.42 × 10⁻³ mmoles hour⁻¹ by corn and soybean roots, respectively.
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