Doctoral Dissertations

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Entomology, Plant Pathology and Nematology

Major Professor

Ernest C. Bernard

Committee Members

Parwinder Grewal, Mark Radosevich, Sean Schaeffer


Modern human civilization occurs at the expense of biodiversity. Human activity has extensively transformed the land surface by agricultural intensification and urbanization. Notably, agricultural practices mainly tillage have diverse impacts on plants, soils and soil organisms. Tillage changes soil properties and affects organisms that are living in the soil. In addition, human activities such as burning of fossil fuels, urbanization, agriculture, deforestation and desertification are rapidly changing the world’s climate through the emission of greenhouse gases. Increase in the emission of greenhouse gases leads to global warming. Increase in air temperature congruently increases soil temperature, which could affect biodiversity in the soil. Nematodes are the most abundant multicellular soil organisms and are morphologically and functionally diverse. The objectives of this study were: 1) to assess the influence of agricultural intensification and urbanization on nematode communities by comparing different ecosystems through meta-analysis of published literature on a global scale, 2) to evaluate the effect of tillage on nematode communities in terms of increasing level of physical disturbance in an undisturbed forest ecosystem and 3) to investigate the response of nematodes to a 5 oC rise in soil temperature by simulating future global warming using heating cables in forest and agricultural ecosystems. Results from the meta-analyses indicated that overall richness was higher in forest than in natural grassland, disturbed grassland, urban, and agriculture ecosystems. In contrast, overall abundance was highest in disturbed grassland, agriculture and forest ecosystems. Effects of tillage on nematode communities suggested that it significantly reduced nematode richness but not abundance. Soil warming in agricultural site did not affect nematode abundance, whereas nematode richness was significantly decreased in the warming treatment. On the other hand, nematode abundance and richness were not affected by soil warming in the forest ecosystem. Results from the warming experiment support the idea that nematode communities in the forest ecosystem may be more resilient to environmental fluctuations than to communitites in agricultural ecosystems. Overall, this research strengthens the concept that human interventions adversely impact nematode richness, which is crucial for the maintenance of the full suite of ecosystem services provided by soil food webs.

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