Impact of Farming Practices on Soil Bacterial Community Composition, Diversity, and Interactions in the Main Agricultural Regions of Alberta

• Author / Creator

  Aguirre Monroy, Angelica M

• Soil health refers to “the capacity of soil to function as a vital living system”, implying not only the capacity of soil to providing services of human interest, but also its capacity to provide ecological services, which makes ecosystems sustainable for the long term. The assessment of soil health in agricultural systems is crucial for the sustainability of both agriculture and soil. While agriculture depends on soil resources and their ability to support plant growth and crop productivity, the intensification of management in these systems represents a stress to the soil environment and can lead to soil degradation. The assessment of soil health could provide insights about the impact of the different agricultural practices on soil attributes. Given that soil health is a non-directly quantifiable feature that reflects multiple soil physical, chemical, and biological attributes, measurable indicators are used as proxies of the soil condition and integrated into single-score indexes. However, many of the developed indexes overlook the role of microbial communities in the soil health. Microorganisms play a crucial role in soil functionality, are involved in biogeochemical cycling, and contribute to the availability of nutrients in soil. They form symbiotic relationships with plants and are basal feeders of trophic networks in these systems. Moreover, microbial communities are sensitive to the changes in the soil environment. Changes in soil microbial communities should therefore provide information regarding shifts in processes occurring in soils from different natural and managed systems. Though, due to functional redundancy in microbial communities, shifts in their structure may be independent from changes in soil processes.

  In Alberta, the Soil Quality Monitoring Program (SQMP) conducted from 1997 to 2007 aimed to characterize soil quality over time from benchmark sites across the province by evaluating multiple soil physico-chemical parameters. However, no biological indicators of the soil quality were included at the time. Given that agricultural practices could affect the soil environment and microbial communities are sensitive to environmental changes, I revisited the SQMP benchmark sites and evaluated bacterial communities from soils undergoing different agricultural practices (i.e., tillage intensity, crop type, herbicide use, and fertilization method). I assessed the effect of agricultural practices on bacterial community composition, heterogeneity, diversity, and co-occurrence via high-throughput sequencing of the 16S rRNA marker gene and statistical and multivariate analyses. pH and ecoregion were important drivers of bacterial community composition. Agricultural practices influenced the heterogeneity and evenness of bacterial communities but did not play a major role in shaping their composition. On the other hand, co-occurrence network analyses revealed that the complexity and behavior of interactions among the members of the soil bacterial community are altered by different agricultural practices. These changes in the community dynamics could indicate changes in microbial functionality, and the capacity of the community to overcome environmental stress, which in turn could influence the functionality of the soil system. Altogether, my results indicate that bacterial community composition is insensitive to different agricultural practices such as tillage, fertilization, crop type and herbicide usage. However, co-occurrence network metrics may be promising indicators of soil health in agricultural systems.

• Subjects / Keywords

  • soil
  • microorganisms
  • DNA
  • high
  • high throughput sequencing

• Graduation date

  Spring 2022

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-fkk5-ar97

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.