Evaluating trait-based ecology in Sphagnum moss

Investigations into the distribution and abundance of non-vascular plants have largely focused on their diversity and productivity in given environments. A trait-based approach, which considers intraspecific variation and evolution of functional traits and how plant–environment interactions influence ecosystem processes has not been explored in this plant group. A way forward is to evaluate moss traits within the context of theories such as resource economics theory (RET) and optimal partitioning theory (OPT), which provide clear mechanistic predictions for pattern of trait responses that reflects the life-history strategies of species. RET posits that plant traits are coordinated for fast or slow resource acquisition and growth strategies. OPT predicts that plants would invest in the organ receiving the most limiting resource. Collectively, these theories can provide insights into how traits influence ecophysiological adaptation of different species and the importance of intraspecific variability in this plant group. In this thesis, I used combinations of factorial and field experiments to evaluate the trait-based ecology in Sphagnum moss traits in the context of the RET and OPT. In the first chapter, I used a factorial experiment involving light, moisture and plant density to test whether two ecologically disparate Sphagnum species conformed to the fast-slow strategies predicted by RET and often observed in vascular plants. Consistent with OPT, Sphagnum diverted biomass from branch to capitulum under moisture stress to optimize atmospheric sources of moisture. In the second chapter, I used factorial experiments involving plant origin (hummock versus hollow), light, and moisture to show that intraspecific trait variability influences the range of environment that Sphagnum occupies within peatland, and therefore matters to the ecophysiology of this plant group. In the third chapter, I explore trait variability in Sphagnum moss at different spatial scales. I found that the traits varied the most within patches, which is the smallest sampling unit but also that the mechanisms controlling different traits may be operating at different spatial scales. Collectively, the studies showed that Sphagnum traits are integrated for performance but that the relationships among traits operates differently from that of vascular plants. Nonetheless, the traits are adaptable to the trait-based framework and could be tested against additional ecological theories.