Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Science

Program

Biology

Supervisor

Zoë Lindo

Abstract

Temperature and moisture are two key factors that are expected to change under current and future climate projections, with significant impacts on ecosystems and biological communities. In northern latitudes, boreal peatlands, known as major carbon stores, are particularly vulnerable to these changes. Changes in temperature and moisture levels are predicted to shift boreal peatlands from carbon sinks to carbon sources by altering decomposition dynamics, primarily through effects on below-ground communities such as microarthropods, as well as effects on below-ground processes such as decomposition and nutrient cycling. Oribatid mites are one of the most dominant microarthropod communities in boreal peatlands as well as other terrestrial systems; they contribute to carbon flux and soil nutrient cycling by feeding on decomposing organic matter and regulating microbial communities. Here, I used both field and controlled lab experiments to study the effects of experimental warming and moisture reduction on oribatid mite communities. I observed significant changes in oribatid mite community composition under warmer temperatures, driven by a decline in diversity and evenness due to an increase in smaller (< 300 μm) oribatid mites. This compositional shift towards smaller oribatid mites also led to a decline in average community body size. Overall, my results show that temperature was a strong driver of shifts in oribatid mite communities in boreal peatlands.

Summary for Lay Audience

The organisms that live in soils are estimated to make up more than half (59%) of all species on Earth. These organisms play important roles, such as breaking down organic debris, cycling soil nutrients, and helping soils store carbon; these processes are essential for the proper functioning of many ecosystems. Recent climate predictions suggest that climate change will impact soil ecosystems, affecting the abundance, richness, diversity, and functions of soil organisms. The effects of climate change on soil organisms will arise through several factors, particularly increases in soil temperature and reductions in soil moisture. Changes in these factors are especially important in wetland systems like boreal peatlands, which are characterised by low temperatures and high moisture conditions. Low temperatures and high moisture slow down decomposition in boreal peatlands; combined with the presence of unique soil organisms, this allows boreal peatlands to hold more carbon than other terrestrial systems, making them significant carbon stores. Climate change is expected to increase temperature and reduce moisture in boreal peatlands, affecting soil organisms in ways that could shift boreal peatlands from carbon stores to carbon sources. To understand how soil organisms in boreal peatlands will respond to climate change, I conducted a field and a lab experiment to mimic future climate conditions, particularly changes in soil temperature and moisture. I focused on oribatid mites, one of the most dominant groups of soil organisms. My results show that temperature was a strong factor affecting oribatid mite communities in boreal peatlands. More specifically, I found that warmer temperatures changed community structure by increasing the abundance of smaller oribatid mites, which in turn reduced overall diversity. This increase in smaller oribatid mites led to a reduction in the average body size of the oribatid mite communities. As one of the dominant groups in soils, changes in oribatid mite communities may alter decomposition and nutrient cycling processes in peatland, ultimately impacting the ability of peatlands to function as long-term carbon storage.

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