Publikationsserver der RWTH Aachen University
Der mikrobielle Umsatz von Ernterückständen in einem landwirtschaftlich genutzten Boden und dessen Beeinflussung durch ausgewählte Xenobiotika
Abstract
dc:descriptionMicroorganisms in agricultural soils are responsible for maintaining soil fertility by participating in many different turnover processes. Along with the degradation of organic matter, humification takes place, plant-available nutrients are released, and the naturally occuring nutrient-cycles are preserved. Cultivation, fertilization, and environmental chemicals may affect the microbial communities and impair these processes. In the thesis presented, the effect of different active substance concentrations of the herbicide Benazolin and the PAH representative Benzo[a]pyrene on microorganisms involved in the turnover of crop residues was investigated in three successive experiments. The experiments were performed as part of the HGF (Helmholtz Association of National Research Centres) project soil functions. In microcosm studies 14C-labelled maize straw was incorportated into typical orthic luvisol to simulate the degradation of crop residues in agricultural soils. Apart from radio-analytical determination of 14C-mineralization rates, microbial activity was assessed by means of DMSO reductase-rates. Fungal biomass was analyzed by means of soil ergosterol contents. Additionally the microbial community structure was characterized by denaturing gradient gel electrophoresis (DGGE) and sequence analyses of 18S rDNA fragments. The experimental results can be summarized as following: Application of Benazolin had a concentration-depended effect on the mineralization of maize straw and on the microbial activity. During the first days after application of the highest applied concentrations of Benazolin (50 and 200 mg kg-1), mineralization of maize straw was reduced. At the same time the lower concentrations of applied Benazolin (1 and 10 mg kg-1) stimulated the 14CO2-releases and highest microbial activities were observed in these treatments. In contrast to the inhibiting effect of high amounts of Benazolin, Benzo[a]pyrene stimulated the turnover of plant material in the concentrations of 50 and 200 mg kg-1. In these treatments also the highest microbial activity was detected. Towards the end of the incubation time of 150 days both xenobiotics induced a concentration-dependent increase of the fungal biomass with the strongest increase in the soils with highest concentrations of Benazolin and Benzo[a]pyrene. However, this had no effect on the structure of the fungal communities, which were similar in all soils treated with maize straw. The DGGE analysis of the 16S rDNA indicated an influence of high concentrations of the applied xenobiotics on the composition of the bacterial communities. Accordingly, Benazolin treatment resulted in a decrease of the amount of bands in the DGGE gel and after application of Benzo[a]pyrene new bands appeared. From gels with amplified DNA from Benazolin and Benzo[a]pyrene treated soils (200 mg kg-1) individual DGGE bands were excised. The DNA from those bands was cloned, sequenced and phylogenetically classified. Only some of these sequences were related to organisms frequently occurring in contaminated soils with organic pollutants. The fungal 18S rDNA fragments, which were representative for all treatments with maize straw, were related to fungi known to degrade lignin and cellulose compounds. The results reveal that the xenobiotics a analyzed are only able to affect the turnover of the maize straw if they are applied at extremely high concentrations. The same is true for the microbial community composition, which was only changed in treatments which received the highest amounts of Benazolin or Benzo[a]pyrene. Overall the possible impact of the applied xenobiotics on the turnover of crop residues and the microbial communities involved can be considered small.
Degree
thesis:*- Grantor dc:publisher
- Publikationsserver der RWTH Aachen University
- Year dc:date
- 2004
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Bulawa, Beata
- Contributors dc:contributor
-
- Schäffer, Andreas
Subjects
dc:subject × 7Rights
dc:rights- Statement dc:rights
-
- info:eu-repo/semantics/openAccess
- Language dc:language
- ger