Soil is an important ecosystem that supports a wide variety of organisms such as bacteria,
fungi, arthropods and nematodes. This sensitive ecosystem may be influenced by various
factors, including agricultural management practices. With the introduction of genetically
modified (GM) glyphosate-tolerant (RoundUp ® Ready: RR) crops, herbicides such as
glyphosate have been increasingly used. However, little is known about the effect of
glyphosate on the biological communities in these herbicide-sprayed soils. With the intimate
proximity that microorganisms and nematodes have with the roots of plants, these
organisms can be used to assess changes that may occur in the soil surrounding roots of
RR crops. The aim of this study was to determine microbial community structure and
nematode diversity, with emphasis on that of non-parasitic nematodes, in soil samples from
conventional soybean (CS) - and RR- soybean fields compared to that in adjacent natural
veld (NV) areas.
Samples were collected from twenty three sites at six localities that are situated within the
soybean-production areas of South Africa. These sites represented fields where RR and CS
soybean grew, as well as surrounding NV. All RR fields have been treated with glyphosate
for no less than five years. Microbial community structures of the twenty three sites in the
RR, CS and NV ecosystems were determined by phospholipid fatty acid (PLFA) analyses.
Nematode diversity was determined by extracting the nematodes from soil samples and
conducting a faunal analysis. Soil physical and chemical properties were determined by an
independent laboratory, Eco-Analytica (North West University, Potchefstroom) according to
standard procedures.
Results from this study indicated differences in microbial community structure between the
various localities. However, there were no significant (p ≤ 0.05) differences in microbial
community structures between RR- and CS ecosystems. Soils of both RR- and CS crops
were primarily dominated by bacteria. Nematode identification and faunal analysis also
indicated no significant (p ≤ 0.05) differences between the different non-parasitic/beneficial
nematodes that were present in soils of these two ecosystems during the time of sampling.
Non-parasitic nematode communities were primarily dominated by bacterivores. A faunal
analysis indicated that most of the sites contained enriched, but unstructured soil food-webs.
However, four of the sites showed enriched and structured food webs due to the presence of
non-parasitic nematodes with high coloniser-persister (cp) values. Relationships between non-parasitic nematode – and microbial communities showed that there was a positive
relationship between nematode functional groups and their corresponding microbial prey.
From the results obtained in this study, it can be concluded that the community structures of
both non-parasitic nematodes and microorganisms shared similarities. These community
structures showed no long-term detrimental effects of glyphosate application in the soils
surrounding roots of RR soybean crops. Relationships existed between non-parasitic
nematode and microbial communities in the rhizosphere of soybean crops and natural veld.
For example, bacterivore nematodes had a strong positive relationship with gram-negative
bacteria. Similar but weaker relationships also existed between carnivores, omnivores, plantparasitic
nematodes and gram-negative bacteria. A positive relationship also existed
between fungivores and fungal fatty acids. This emphasises the value of these organisms as
indicators of soil health and also the impact that agricultural practices can have on soils. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2014
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:nwu/oai:dspace.nwu.ac.za:10394/13339 |
| Date | January 2014 |
| Creators | Jansen, Chantelle |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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