Plant and Soil

, Volume 38, Issue 1, pp 161–175 | Cite as

Diffusion of phosphate to plant roots in soil

I. Quantitative autoradiography of the depletion zone
  • K. K. S. Bhat
  • P. H. Nye
Article

Summary

Improved resolution in autoradiography, achieved by the use of the low β energy isotope, P33, as tracer for soil phosphorus, enables the exchangeable phosphorus in a soil block to be measured quantitatively. A technique is described for the autoradiography of the P-depletion zone around the roots growing in soil, from which the P gradients are measured by microdensitometry.

The amounts of P taken up by rape (Brassica napus) on a P-treated Begbroke Sandy Loam compared well with that removed from the soil as measured from the autoradiograph of the depletion zone. The P gradient around the roots suggests intense root hair activity; but the zone of depletion extended well beyound the tips of root hairs. The experimentally observed gradient is much closer to the one predicted from diffusion theory considering uniform depletion from within the equivalent root hair cylinder, than to the one obtained assuming the root hairs are inactive.

A rapid depletion of up to about 60 per cent of the exchangeable P was observed within the root hair cylinder during the initial 3 days of absorption. The corresponding concentration of P in solution within the cylinder determined from a desorption isotherm, is hence brought down to a low level very rapidly, and is held at or near this level at later periods. The amounts transferred into the root hair cylinder from outside as calculated from a diffusion model were lower than the experimental values. It is suggested that the discrepancy may lie in the calculation of the effective diffusion coefficients for P in the soil from a P-desorption isotherm, owing to difficulties involved in simulating the root environment in the desorption isotherm experiment

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References

  1. 1.
    Bagshaw, R., Vaidyanathan, L. V., and Nye, P. H., The supply of nutrient ions by diffusion to plant roots in soil. VI — Effects of onion plant roots on pH and phosphate desorption characteristics in a sandy soil Plant and Soil 37, 627–639 (1972).Google Scholar
  2. 2.
    Barber, D. A., The influence of the microflora on the accumulation of ions by plants. In Ecological Aspects of the Mineral Nutrition of Plants. Blackwell Publ., Oxford, 191–200 (1969).Google Scholar
  3. 3.
    Doniach, M. C. and Pelc, S. R., Autoradiograph technique. Brit. J. Radiol. 23, 184–192 (1950).Google Scholar
  4. 4.
    Drew, M. C. and Nye, P. H., The supply of nutrient ions by diffusion to plant roots in soil. II — The effect of root hairs on the uptake of potassium by roots of rye grass (Lolium multiflorum). Plant and Soil 31, 407–424 (1969).Google Scholar
  5. 5.
    Drew, M. C. and Nye, P. H., The supply of nutrient ions by diffusion to plant roots in soil. III — Uptake of phosphate by roots of onion, leek and rye-grass. Plant and Soil 33, 545–563 (1970).Google Scholar
  6. 6.
    Drew, M. C., Nye, P. H., and Vaidyanathan, L. V., The supply of nutrient ions by diffusion to plant roots in soil. I — Absorption of potassium by cylindrical roots of onion and leek. Plant and Soil 30, 252–270 (1969).Google Scholar
  7. 7.
    Lewis, D. G. and Quirk, J. P., Phosphate diffusion in soil and uptake by plants. III — P31 movement and uptake by plants as indicated by P32-autoradiography. Plant and Soil 26, 445–453 (1967).Google Scholar
  8. 8.
    Mayr, J., Advantages given by P33-or aged P32-in autoradiography. Experimentia 12, 298–299 (1956).Google Scholar
  9. 9.
    Nye, P. H., The effect of nutrient intensity and buffering power of a soil, and the absorbing power, size and root hairs of a root, on nutrient absorption by diffusion. Plant and Soil 25, 81–105 (1966).Google Scholar
  10. 10.
    Nye, P. H. and Marriott, F. H. C., A theoretical study of the distribution of substances around roots resulting from simultaneous diffusion and mass flow. Plant and Soil 30, 459–472 (1969).Google Scholar
  11. 11.
    Olsen, S. R. and Watanabe, F. S., Diffusive supply of phosphorus in relation to soil textural variations. Soil Sci. 110, 318–328 (1970).Google Scholar
  12. 12.
    Place, G. A., Phillips, R. E. and Brown, D. A., Self-diffusion of phosphorus in clays and soils. II — The effect of pH. Soil Sci. Soc. Am. Proc. 32, 657–659 (1968).Google Scholar
  13. 13.
    Vasey, E. H. and Barber, S. A., Effect of placement on the absorption of Rb86 and P32 from soil by corn roots. Soil Sci. Soc. Amer. Proc. 27, 193–197 (1963).Google Scholar
  14. 14.
    Whitehouse, W. J. and Putman, J. L., Radioactive Isotopes O.U. Press, London (1953).Google Scholar

Copyright information

© Martinus Nijhoff Publishers 1973

Authors and Affiliations

  • K. K. S. Bhat
  • P. H. Nye

There are no affiliations available

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