The rhizosphere has biological, chemical and physical properties that differ from those of bulk soil and which influence the availability of water and nutrients. Mucilage produced by roots contains a surface active agent which reduces the surface tension around the root. The presence of root cap cells in the mucilage gives it viscoelastic properties which draw soil particles towards the root surface and, together with the increasing viscosity as the soil dries and mucilage dehydrates, facilitates the formation of rhizosheaths.The development of non-invasive imaging allied with computed tomography (CT) has allowed the study of root systems in situ and the observation of root growth. It is now possible to achieve cone beam images in a scanning time of 30 minutes with a resolution of 100 .m. Further developments of this technique should allow changes in bulk density and water content close to the root surface to be observed and quantified.
Anderson, M. A., Hung, A. Y. C., Mills, D., Scott, M. S. (1995): Factors affecting the surface tension of soil solutions and solutions of humic acids. Oil Sci., 160, 111-116.
'Factors affecting the surface tension of soil solutions and solutions of humic acids ' () 160 Oil Sci. : 111 -116 .
Paton, G. I., Rattray, E. A. S., Campbell, C. D., Cresser M. S., Glover L. A., Meeussen, J. C. L., Killham, K. (1997): Use of genetically modified microbial biosensors for soil ecotoxicity testing. In: Pankhurst, C., Doube, B., Gupta, V. (eds.) Biological Indicators of Soil Health and Sustainable Productivity. CAB International, Wallingford, pp. 397-418.
Biological Indicators of Soil Health and Sustainable Productivity , () 397 -418 .
Hainsworth, J. M., Aylmore, L. A. G. (1983): The use of computer-assisted tomography to determine spatial distribution of soil water content. Aust. J. Soil Res., 21, 435-443.
'The use of computer-assisted tomography to determine spatial distribution of soil water content ' () 21 Aust. J. Soil Res. : 435 -443 .
Hamza, M., Aylmore, L. A. G. (1992): Soil solute concentration and water uptake by single lupin and radish plant roots. I. Water extraction and solute accumulation. Plant and Soil, 145, 187-196.
'Soil solute concentration and water uptake by single lupin and radish plant roots ' () 145 I. Water extraction and solute accumulation. Plant and Soil : 187 -196 .
Heeraman, D. A., Hopmans, J. W., Clausnitzer, V. (1997): Three dimensional imaging of plant roots in situ with X-ray computed tomography. Plant and Soil, 189, 167-179.
'Three dimensional imaging of plant roots in situ with X-ray computed tomography ' () 189 Plant and Soil : 167 -179 .
Hinsinger, P. (1998): How do plants acquire mineral nutrients? Chemical processes involved in the rhizosphere Adv. Agron., 64, 225-265.
'How do plants acquire mineral nutrients? Chemical processes involved in the rhizosphere ' () 64 Adv. Agron. : 225 -265 .
Jenneson, P. M., Gilboy, W. B., Morton, E. J., Luggar, R. D., Gregory, P. J., Hutchinson, D. (2000): Optimisation of X-ray micro-tomography for the in situ study of the development of plant roots. I.E.E.E. (In press).
'Optimisation of X-ray micro-tomography for the in situ study of the development of plant roots ' () I.E.E.E. .
Lynch, J. M. (1990): The Rhizosphere. Wiley Interscience, Chichester, UK.
The Rhizosphere , ().
McCully, M. E. (1995): The efflux of water from the surface of field-grown maize roots. Physiol. Plant., 95, 217-224.
'The efflux of water from the surface of field-grown maize roots ' () 95 Physiol. Plant. : 217 -224 .
Passioura, J. B. (1988): Water transport in and to roots. Annu. Rev. Pl. Physiol. Pl. Molec. Biol., 39, 245-265.
'Water transport in and to roots ' () 39 Annu. Rev. Pl. Physiol. Pl. Molec. Biol. : 245 -265 .
Read, D. B., Gregory, P. J., Bell, A. E. (1999): Physical properties of axenic maize mucilage. Plant and Soil, 211, 87-91.
'Physical properties of axenic maize mucilage ' () 211 Plant and Soil : 87 -91 .
Watt, M., McCully, M. E., Canny, M. J. (1994): Formation and stabilisation of rhizosheaths in Zea mays L. Effect of water content. Plant Physiol., 106, 179-186.
'Formation and stabilisation of rhizosheaths in Zea mays L. Effect of water content ' () 106 Plant Physiol. : 179 -186 .
Young, I. M. (1995): Variation in moisture contents between bulk soil and the rhizosheath of wheat (Triticum aestivum L. cv. Wembley). New Phytol., 130, 135-139.
'Variation in moisture contents between bulk soil and the rhizosheath of wheat (Triticum aestivum L. cv. Wembley) ' () 130 New Phytol. : 135 -139 .
Read, D. B., Gregory, P. J. (1997): Surface tension and viscosity of axenic maize and lupin mucilages. New Phytol., 137, 623-628.
'Surface tension and viscosity of axenic maize and lupin mucilages ' () 137 New Phytol. : 623 -628 .
Asseng, S., Aylmore, L. A. G., MacFall, J. S., Hopmans, J. W., Gregory, P. J. (1999): Computer assisted tomography and magnetic resonance imaging. In: Techniques for Studying Roots (in press).
Techniques for Studying Roots , ().
Aylmore, L. A. G. (1993): Use of computer-assisted tomography in studying water movement around plant roots. Adv. Agron., 49, 1-54.
'Use of computer-assisted tomography in studying water movement around plant roots ' () 49 Adv. Agron. : 1 -54 .
Bhat, K. K. S., Nye, P. H. (1973): Diffusion of phosphate to plant roots in soil. 1. Quantitative autoradiography of the depletion zone. Plant and Soil, 38, 161-175.
'Diffusion of phosphate to plant roots in soil ' () 38 1. Quantitative autoradiography of the depletion zone. Plant and Soil : 161 -175 .
Bowen, G. D., Rovira, A. D. (1991): The rhizosphere: the hidden half of the hidden half. In: Waisel, Y., Eshel, A., Kafkafi, U., (eds.) Plant Roots: The Hidden Half. Marcel Dekker Inc., New York, pp. 641-670.
Plant Roots: The Hidden Half , () 641 -670 .
Foster, R. C. (1986): The ultrastructure of the rhizoplane and rhizosphere. Annu. Rev. Phytopathol., 24, 211-234.
'The ultrastructure of the rhizoplane and rhizosphere ' () 24 Annu. Rev. Phytopathol. : 211 -234 .
Gregory, P. J., Hinsinger, P. (1999): New approaches to studying chemical and physical changes in the rhizosphere. Plant and Soil, 211, 1-9.
'New approaches to studying chemical and physical changes in the rhizosphere ' () 211 Plant and Soil : 1 -9 .