Die Bedeutung der Rhizosphäre von Bromus mollis L. als Ort erhöhter mikrobieller Aktivität im Boden für eine mögliche Mineralisation von Xenobiotika

In the presented study the connection between root growth and degradation of xenobiotics in the rhizosphere of Bromus mollis L. (Poacea) has been investigated with an especially assembled experiment. The regular root system (secondary homorhizie) of the test plant as well as the sufficient production rate of the root-biomass (about 200 mg/ g soil dry weight (dw) within 9 weeks) under given test conditions and given testing time have been important conditions for significant and reproducible test results. At first root surface growth and root development have been investigated in root-development-tests. Parallel to the analyse of root development the microbial abundance (measurement of total bacteria number) as well as the microbial activity (substrate induced respiration and reductase activity) in the soil and rhizosphere respectively have been registered. The parallel measurement of the parameter at different sowing densities was used to eliminate methodical errors as well as to statistically ensure the results. Independent of the sowing density the microbial parameter correlate with a rise of the density of roots up to a root-surface of 4000 to 5000 cm2 per g soil dw. The abundance of microorganisms in the planted soil reached three times the amount (n = 16 x 10E9 x gE-1) of the unplanted control whereas the rates of both physiological parameters reached one and a half times the amount (reductase activity: DMS / dw soil x t = 600 ng / g x h respectively substrate induced respiration: CO2 / dw soil x t = 0.06 mg / g x h). The degradation rate of the rhizosphere of Bromus mollis was tested by using 14C-labeled chemicals in basically same built and controlled ventilated model ecosystems. The comparison of both test series enables a correlation between root development of Bromus mollis and degradation rate of organic substances in the rhizosphere. The same kind of "natural" soil has been used in both test series (root-development-tests and degradation tests). It was taken from a loamy farmland location. By using soil with a natural composition and structure as well as a natural population of microorganisms to begin with enabled a transferability of the results towards outdoor conditions despite of the prevailing standardized laboratory conditions. With p-nitrophenol and pyrene two different persistent 14C-labeled chemicals were used as xenobiotics. P-nitrophenol as a metabolite of parathion for example represents a pesticide-transformation-product. Pyrene has been used exemplary for the widespread substance-group of polycyclic aromatic hydrocarbons (PAH's). The degradation rate of the rhizosphere of Bromus mollis concerning these two xenobiotics shows significant differences: Compared to the unplanted control, the degradation of p-nitrophenol in the rhizosphere-system was only slightly increased. This can be explained by the fast degradation of p-nitrophenol by non-rhizosphere microorganisms. Within the first week - at a time when Bromus mollis only just germinated - 80% of the applied amount of 14C-p-nitrophenol were already mineralised. When using the more persistent xenobiotic pyrene the rhizosphere-effect could be clearly made out. Here the rate of mineralization in the rhizosphere-system was about 40% of the applied amount of 14C-pyrene and by that 30% higher than in the unplanted control test after seven weeks. The correlation of the mineralization of the degradation tests with the development of the reductase activity and substrate induced respiration respectively in the root-development-tests shows a direct proportionality between degradation capacity and microbial activity in the rhizosphere. Compared to that the abundance of microorganisms as a measured parameter does not show the development of the degradation capacity in a sufficient way. The root-development-tests as well as the degradation tests show that the increasing activity of the microorganisms is casually connected with the increased degradation capacity and that it is indirectly caused by the structural and physiological changes in the root system of Bromus mollis. The root surface as a measured parameter allows only limited conclusions concerning the degradation capacity of the rhizosphere of Bromus mollis. To achieve a better understanding of the interactions in the rhizosphere, a characterization of the physiological condition (of parts) of the roots as well as the measuring of the root surface should be included in future experiments.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2003

Author dc:creator

• Aletsee, Manfred

Contributors dc:contributor

• Schuphan, Ingolf

• info:eu-repo/classification/ddc/570
• Biowissenschaften, Biologie
• Rhizosphäre
• Dekontamination
• Bromus mollis
• p-Nitrophenol
• Pyren
• Xenobiotika
• Abbau

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-123758%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:62168