Eine Kultivierungsmethode zur Untersuchung von Phytohormoneffekten auf Rhizosphärenprozesse

Higher plants affect processes in the rhizosphere by root exudation. The exuded compounds may directly influence nutrient availability or may serve as a substrate for various nutrient-solubilizing soil microorganisms. Furthermore, plant growth promoting effects of rhizosphere microbes include the production of a vast range of metabolites (biological active substances) that may affect plant growth directly after being taken up by the plant, or indirectly by modifying the soil environment. Phytohormones like auxines (indole-3-acetic acid, IAA), gibberellins (gibberellic acid, Ga₃) or cytokinins (trans-zeatin, t-Z) belong to this groups of substances. It is well documented that cultures of several plant growth promoting microorganisms produce these phytohormones in considerable amounts. But there are only few data available about long-term effect of these coumpounds on rhizosphere processes of intact plants.In the present investigation, four cultivars of maize plants (Zea mays L.) were grown in a greenhouse pot experiment with coarse sand as substrate. Control plants were supplied with nutrients by daily watering with a nutrient solution (40 mg P/1) and P-deficient plants were cultivated in a substrate containing 324 mg of sparingly soluble Ca₃ (PO₄)₂ (65 mg P). Additionaly, the concentration of IAA, GA₃ or t-Z in the rhizosphere of maize plants was maintained at 0.1 mM (IAA, GA₃) or 0.01 mM (t-Z) by daily addition of a freshly mixed hormone-containing nutrient solution to one half of each P treatment. Three factorial analysis of variance showed significant effects of hormone treatment, P availability, and genotype on growth of maize plants indicating that the presented method is suitable for induction and investigation of long-term hormone effects on rhizosphere processes of higher plants.