How do pesticides impact soil microbial structure and functioning?
Howell, Christopher Carl (2011) How do pesticides impact soil microbial structure and functioning? PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b2568654~S1
Pesticides are used worldwide and exhibit a plethora of different modes of action against a wide
spectrum of organisms. Therefore, before they can be marketed they have to be tested against certain
standardised regulations. These include the Food and Environment Protection Act 1985 (FEPA), the
Control of Pesticides Regulations 1986 (COPR), and more recently the European Council Directive
1991 91/414 and the Plant Protection Products Regulations 1991 (PPPR). However, the current tests
used to determine pesticide impacts on microorganisms as detailed by the OECD focus on only broadscale
analytical methods that may mask more subtle effects that may still be ecologically significant.
Therefore, this project aimed to determine the effects of a widely-used model pesticide, azoxystrobin
on both target and non-target microbial communities across different trophic levels.
The techniques used to perform this included broad- (soil microbial biomass and soil dehydrogenase
activity) and fine-scale (T-RFLP, cloning/sequencing, and qPCR) analytical methods. The results of
these analyses showed that the application of azoxystrobin had a significant, concentration-dependent
impact on soil dehydrogenase activity whilst biomass was unaffected. The molecular analyses showed
that azoxystrobin significantly impacted fungal community structure, diversity and gene copy number.
Additionally, pesticide application significantly altered nematode community structure and general
eukaryotic diversity. Soil and liquid culture enrichments showed that azoxystrobin degradation can be
enhanced following repeated applications and enabled the isolation of two degrader organisms with
sequence homologies to a Cupriavidus sp. and a Rhodanobacter sp. Further work showed that
sequential enrichments with azoxystrobin also conferred cross-enhanced degradative abilities for three
other strobilurin fungicides: pyraclostrobin, kresoxim methyl and trifloxystrobin. The work performed
in this thesis served to illustrate how the current OECD test procedures may benefit from the
incorporation of finer-scale molecular methods into its tests, as well as how difficult the task can be to
produce compounds that persist in the environment long enough to perform their required function,
but do not have significant deleterious impacts on non-target organisms when present.
|Item Type:||Thesis or Dissertation (PhD)|
|Subjects:||S Agriculture > S Agriculture (General)|
|Library of Congress Subject Headings (LCSH):||Pesticides -- Testing, Agricultural microbiology|
|Official Date:||September 2011|
|Institution:||University of Warwick|
|Theses Department:||School of Life Sciences|
|Supervisor(s)/Advisor:||Bending, G. D. (Gary D.) ; K. T. (Kirk T.)|
|Sponsors:||Biotechnology and Biological Sciences Research Council (Great Britain) (BBSRC)|
|Extent:||xxiv, 305 leaves : ill., charts|
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