Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Biology

Supervisor

Lindo, Zoë

Abstract

Boreal peatlands are important ecosystems for carbon cycling, storing 1/3 of the world’s terrestrial carbon in only ~3% of the globe, making them a key component of potential mitigation strategies in response to global climate warming. Experiments have shown that warming can affect plant and microbial communities in ways that potentially shift peatlands from carbon sinks to sources. Soil food webs, including the microarthropod community, are key in carbon cycling but are relatively understudied both in peatlands and under experimental warming. My research capitalized on a large-scale experimental field manipulation of warming in two contrasting peatland sites in Northern Ontario, and addressed: 1) the diversity of oribatid mites in Canadian peatlands, 2) factors that drive litter decomposition and oribatid mite communities, by examining different microhabitats, 3) how these communities shift under experimental warming, and 4) the carbon flux in the soil food web, using energetic models for natural and warmed conditions. My published synthesis of oribatid mites in peatlands of Canada updates the species records from 71 to 186 species. I also show that peatland oribatid mite communities are driven by soil moisture and temperature, and that responses to warming are species- and site-specific. Oribatid mite community composition is driven by interactions between temperature and moisture, and dependant on peatland type, leading to the conclusion that oribatid communities follow a species sorting metacommunity paradigm driven by environmental filters. Models of carbon flux suggest that compositional changes in the soil food web under warming will significantly alter carbon cycling and potentially the carbon storage potential of peatlands. Using field experiments alongside modelling approaches for soil fauna, my research provides a comprehensive view of the role of peatland microarthropods and their relation to ecosystem processes under environmental changes. My work is also novel because soil systems are often treated as a ‘black box’ in global change carbon models; thus, my work is the first to link changes in peatland soil biodiversity to carbon storage and release.

Summary for Lay Audience

Peatlands are wetland ecosystems with a high-water table that are important for carbon cycling because of a large organic soil layer composed of partially decomposed plant material called peat. In the boreal zone, peatlands store 1/3 of the world’s terrestrial carbon, but only occupy ~3% of the globe. This ability to store high amounts of carbon in relatively small areas confer boreal peatlands the property of acting as a key component of mitigation strategies in response to global climate warming. This is because by storing more carbon than releasing carbon, less carbon is then in the atmosphere to drive higher temperatures. Different microbial, animal and plant species inhabit peatlands, and they are also involved in this carbon storage ability. Studies have shown that higher temperatures can change the plant and microbial types that dominate peatlands, and this change can thus alter the carbon cycle, but studies demonstrating how warming will affect peatland invertebrates are scarce. My thesis focuses on oribatid mites, which are small arachnids related to spiders, but are involved more directly in carbon cycling. I describe their diversity in two contrasting peatland sites in Northern Ontario, and show that oribatid mites of peatlands in Canada are more diverse than we thought, the fauna includes specialist as well as generalist species, and also that species that reproduce asexually tend to dominate. Using a climate change experiment in both sites, I show that warming and warming-induced moisture reduction have variable effects on oribatid mite communities that depend on species and peatland type. I then confirm that moisture has a more important influence on oribatid mite communities than plant litter type when assessing the oribatid mite fauna in litterbags. Finally, I use food web energetic models to show that changes in oribatid mite community composition caused by warming and warming-induced moisture reduction are suggested to alter the carbon cycling and potentially the carbon storage potential of peatlands.

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