Sphagnum is an important peat-forming group of mosses that often dominate northern peatlands. There has been great interest in understanding Sphagnum traits and its influence on ecosystem processes. However, most research has focused on interspecific variation, contrasting species that occupy different microtopographic positions. Here we used Sphagnum fuscum and Sphagnum magellanicum to explore intraspecific variation in traits related to ecohydrology (hyaline cell density, water retention). We also explored S.fuscum C:N and potential CO2 production rates as measures of tissue decomposability. We asked whether there was meaningful intraspecific variation in traits, and if so, to explore the spatial scale of variation. We implemented a hierarchical design in which we quantified traits at three spatial scales: 1) between individuals within 8 cm diameter patches, 2) between replicate patches located within a single hummock or hollow location, and 3) between hummocks (S.fuscum) or hollows (S.magellanicum).
Results/Conclusions
For both species, we found that the majority of variation in traits consistently occurred within patches, our smallest sampling unit. In S.magellanicum, 55-73% of the total variance in ecohydrological traits occurred within patches, 13-24% of variance occurred between-patches, and 0.1-32% occurred between hollows. In S.fuscum, variance in ecohydrological traits between-patches or between-hummocks were negligible, while variance within-patches was high (73–100% of total variance in traits). C:N varied more within-patches (63% of variance) than between patches or between hummocks, while CO2 production rates varied more between-patches (70% of total variance) than at the other scales. Tissue decomposability positively correlated with tissue water content (r2 = 0.5, p = 0.0005).
Traits also varied considerable between species. Capitula mass and whole-plant dry weight of S.magellanicum were typically more than double that of S.fuscum. Individuals of S.magellanicum had greater moisture retention rates relative to S.fuscum individuals. Our results suggest that intraspecific trait variation is mostly influenced by fine scale heterogeneity. For example, we measured tremendous variability in Sphagnum traits within individual hummocks; remarkably this variation is consistent and repeated across hummocks. Currently we are using multiple experimental approaches to partition genetic and environmental effects on traits. Our long-term goal is to understand how variation in these traits is affected by natural selection, and in turn how it influences resource dynamics and ecosystem-level processes.