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The effect of increased mechanical impedance on pH and release of organic substances by roots of maize grown in nutrient solution was studied. pH of the nutrient solution and release of water soluble and insoluble exudates per unit of root weight increased as mechanical impedance increased. Root and top growth was reduced with increasing mechanical impedance.
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Rola rizosfery w mineralnym odzywianiu sie roslin

86%
The biology and chemistry of the soil-root interface (rhizosphere) has recently received increased attention. Of special interest is the identification and quantification of organic and inorganic root exudates, which may alter the flow of nutrients in the rhizosphere mainly via soil pH and ionic concentration changes in the rhizosphere soil. Release of inorganic ions, such as H⁺ abd HCO₃⁻ , resulted from ion uptake by roots directly affects the pH of rhizosphere soil what can modify the acquisition of nutrients by plants. Exudation of organic compounds by roots may influence the ion solubility and uptake through their indirect effects on microbial activity, physical properties of rhizosphere and dynamics of root growth and directly through the acidification, chelation, precipitation and oxidation-reduction reactions in the rhizosphere. Plant roots release a variety of organic substances; however, the water soluble compounds are most readily decomposable substances which serve as a source of nutrients for microbial populations of microorganisms colonizing root surface. The microorganisms in turn can affect the growth and physiology of plants either directly via various microbial metabolites or by modifying the soil-root interface environment. Although the rhizosphere studies are difficult, understanding the biology and chemistry of rhizosphere is essential to determining the mobility and availability of mineral elements at the soil-root interface and their impact on plant nutrition.
The studies were carried out in laboratory conditions. Poa pratensis root exudates were obtained in the CRETS (continuous root exudate trapping system) and then in glass platter experiment was determined their biological activity in biotest on seed germination, length of roots and height of Phleum pratense seedlings. In the experiment were used the following concentrations of Poa pratensis root exudates: 0,80%, 0,40% and 0,20%. Conducted studies showed that higher concentrations of Poa pratensis root exudates (0,80% and 0,40%) caused total inhibition of germination. Lower concentrations of exudates significantly limited number of germinated seeds and inhibited of root elongation and growth of tested species seedlings. These results indicate that Poa pratensis root exudates seem to include chemical compounds of allelopathic nature.
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Mikoryza wezikularno-arbuskularna roslin zielnych

72%
Probably all gymnosperms and about 85% angiosperms are able to form mycorrhizae. All terrestial gymnosperms seem to require mycorrhizae for survival and reproduction in the natural environment. Most of the herbaceous plants are exlusively VAMF partners. The VAM fungi show a wide distribution - they belong to several genera of the Zygomycetes, Glomales and Gigasporinae orders. They are obligatory biotrophic organisms, acquiring nutritional elements from living cells of plant roots. The interaction between root cells and arbuscular mycorrhizal fungi changes: quantity and quality of roots exudates; transportation of carbon between leaves, stalks and roots of plants, uptake of P, N and microelements by plants. The root colonization by symbiotic fungi contributes to biocontrol of plant pathogens, decrease of water deficiency stress and toxicity of heavy metals to plants. Plant roots colonization by VAM fungi is controlled by molecular signals. These signals reach both the fungal spores and intracellular receptors of plants on specific points on the membrane. Molecular signals from VAM fungi induce expression of specific plant symbiosis genes controlling establishment and effectiveness of mycorrhiza.
The purpose of the studies conducted in the years 1996 - 1998 was to determine the composition of bacteria and fungi populations in the rhizosphere of winter wheat, spring wheat, soybean and potato, and in non-rhizosphere soil. Besides, the effect of root exudates of these plants on the formation of pathogenic fungi communities was established. The microbiological analysis showed that the greatest total number of bacteria was found in the rhizospheres of potato and soybean, and the lowest number in non-rhizosphere soil. The smallest total number of fungi was found in the rhizosphere of winter wheat, and the largest in the rhizosphere of soybean. Pathogenic fungi dominated in the rhizospheres of soybean and potato, while non-rhizosphere soil was the poorest in these microorganisms. Among the pathogenic fungi, Fusarium oxysporum, F. culmorum and F. solani were most frequently isolated. Soybean roots exudated the greatest amount of aminoacids, and acidie aminoacids, which have a positive effect on the development of phytopathogens, dominated in their content. On the other hand, the best quantitative and qualitative composition of aminoacids was found out in the root exudates of winter wheat, since they contained big amounts of alkaline and aromatic aminoacids.
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