The uptake of colloidal organic substances by plant roots as shown by experiments with $^{14}$C-labelled humus compounds
Führ, F.
Sauerbeck, D.
Publikationen vor 2000; PRE-2000; Retrocat
Jülich Kernforschungsanlage Jülich, Verlag 1967
12 p.
Report
Book
ohne Topic
Berichte der Kernforschungsanlage Jülich 490
OpenAccess
Please use the identifier: http://hdl.handle.net/2128/14616 in citations.


In their natural growth medium, plant roots are confronted with mineral compounds as well as with colloidal soll organic matter. Contrary to the known importance ofmineral nutrients, the immediate influence of organic compounds of the growth medium on plant metabolism is as yet a matter of debate. That plant roots are in fact able to absorb organic molecules up to a considerable size is demonstrated sufficiently. Whether this is tme even for colloidal soll organic matter compounds has been investigated using $^{14}$C-labelled humus substances. Substances of this kind, if dissolved in nutrient solutions, are fixed to a considerable extent by plant roots. However, only a small portion can be translocated to the plant tops, depending on the molecular weight of the material applied. Most of the fixed radiocarbon remains on or in the plant roots and cannot be redissolved in water. Because of the colloidal nature of the compounds applied, this insolubility in water does not prove a true uptake. Obviously precipitation reactions occur within the root surface, rendering the material insoluble in neutral solutions. With different solvents as used for the extraction of soll organic matter a karge portion of the root-fixed labelled compounds can be removed. However, depending on the alkalinity of such solvents, the root tissue itself is attacked. This makes it difficult to differentiate exactly between adsorbed and ttuly absorbed radiocarbon. Tissue radioautographs of roots and root organs also show that most of the labelled material is irreversibly fixed on or in the root epidermis. Only smaller molecules such as the so-called "fulvic acids" can penetrate through the root epidermis and may even reach the central cylinder. The distribution pattern of the different materials applied is rather typical and proves the assumption that the metabolic influence of soll organic matter an plant growth is mainly due to its low molecular compounds.