Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Science

Program

Biology

Supervisor

Lindo, Zoë.

Abstract

Plant community composition, of particularly the Sphagnum mosses, is a key regulator of peatland ecosystem dynamics. Sphagnum traits related to growth and water-holding/acquisition dynamics will determine species-specific responses to increases in temperature. To understand plant community dynamics in response to seven years of experimental field warming, I quantified the composition of the vascular and bryophyte communities and measured key Sphagnum traits. I found that the frequency of bare peat increased under warming indicating a loss of Sphagnum coverage, specifically I observed decreases in the abundance of the Sphagnum species S. angustifolium. In warmed plots I also found trends of decreasing S. fuscum, but slight increases in S. divinum that are likely related to water holding capacity traits. My results suggest a transition of peatland plant community composition that may have consequences for the stability of these ecosystems as they experience climate change.

Summary for Lay Audience

Peatlands are wetland ecosystems where the rate of plant matter growth exceeds what is being decomposed. This results in more carbon being stored within the soil than what is released to the atmosphere, making peatlands key sinks of carbon. There are three key factors that keep rates of decomposition low: cool temperatures, high moisture levels, and a group of plant known as Sphagnum mosses. The Sphagnum mosses are ecosystem engineers of peatlands, and their traits have significant influence on regulating water-dynamics, decreasing vascular plant cover, and reducing rates of decomposition. Sphagnum species in peatlands are predominantly determined by moisture gradients and form structures known as hummocks (dry-adapted species: S. fuscum), hollows (wet-adapted species: S. angustifolium), and the space in-between these two extremes, lawns (generalist species: S. divinum). Sphagnum traits are significantly different between species, and this is related to their position along the moisture gradient and help create feedbacks to peatland ecosystem processes like water storage and carbon dynamics. To appropriately understand how carbon storage in peatlands will be affected by climate warming it is critical to identify how the Sphagnum community is changing, which species are driving these changes, the mechanisms (their traits) causing these shifts, and if these traits are changing in response to warming. To identify these shifts, I utilized a long-term climate warming experiment that increased both air and soil temperatures. I found that Sphagnum abundance significantly decreased under warming and this was being driven by losses in the moisture-adapted species S. angustifolium; there were no significant changes in abundance in either S. divinum or S. fuscum. Warming itself did not significantly affect species traits, but there were significant trait differences between species related to their ability to acquire and store water. The likely mechanisms causing the decreases in S. angustifolium relate to their poor ability to store and acquire water from the environment. This research highlights the importance of understanding the species-specific responses of Sphagnum to environmental pressures to accurately identify how the structure and functioning of peatlands will be affected by climate change in the future.

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