Molecular Analysis of Soil Mesofaunal Diversity and the Effects of Natural Capital in Agroecosystems

Abstract

Soil biodiversity is key to maintaining ecosystem functions, but is threatened by anthropogenic changes. To help mitigate these risks, retaining small habitat patches within agroecosystems is a promising method, but it can be challenging to study due to the vast diversity of soil organisms. One important, but understudied, group that contributes to ecosystem functions, such as contributing to soil structure and cycling nutrients in the soil, is the soil mesofauna (~0.2 - 2 mm in size), mainly consisting of mites and springtails. DNA metabarcoding is a tool that is increasingly used to expand our knowledge of biodiversity, but it is still a work in progress with respect to investigating soil mesofaunal communities. A comparison of this technique performed on bulk mesofauna specimens versus bulk soil samples, collected in 2021 from an intensively farmed area of Eastern Ontario, found differences in species richness, but nonetheless, similarities were detected in community composition between both methods (Chapter 2). Identifying specimens morphologically gave different results compared to both molecular methods. During the summer of 2022, a survey of mesofauna in four types of non-field habitats (ditch margins with and without trees, small forest patches, and larger forest patches) was conducted in the same region (Chapter 3). Although the number of mesofaunal species was highly variable across all the sites surveyed, differences were detected in community composition between forested and unforested sites. The communities were highly variable within each habitat type. The lack of overlap in species presence between the different sites could be due to a variety of factors, such as the small-scale habitat features of the sites or differences in microhabitats between samples. As well, there was no clear separation between small and large forest patches with respect to mesofaunal community composition, which showcases the value that even small patches of natural habitat can have within agroecosystems. Soil physicochemical properties, particularly organic matter, moisture, and cation exchange capacity (CEC), also influenced these communities, while there was little evidence that the mesofaunal community varied over the growing season. This thesis improves understanding of soil mesofaunal diversity and community composition within agroecosystems in Canada, which remain largely uncharacterized. DNA metabarcoding yields insights into species composition of soil mesofaunal communities that are elusive, at best, using traditional morphological techniques.