Getting to the root of the matter: Variations in vascular root biomass and production in peatlands and responses to global change.

摘要

Root biomass, production and decomposition have been poorly studied in peatland ecosystems despite evidence that they may be equal to or greater than aboveground vascular plant components and contribute significantly more carbon (C) to the soil organic matter pool. At the same time, global change phenomena such as water table drawdown (via rising temperatures) and increased nitrogen deposition threaten to dramatically alter these systems, primarily through changes to vegetation. This makes quantifying root biomass, production, and decomposition critical to our understanding of peatland C cycles. Understanding how these belowground stocks and fluxes vary with aboveground plant components in relation to environmental (climate, water table) and biological (vegetation type, species diversity) factors can provide insight into how peatland plant communities adapt to different environments. Additionally, the implications of these adaptations to C cycling within and among sites and in response to global change phenomena can then be considered.;My results indicate that the majority of vascular plant biomass in wetlands is located belowground while the majority of production occurs aboveground. Belowground biomass and production were positively related to aboveground biomass and production. Both temperature and precipitation were consistently significant predictors of biomass and production as well as vegetation type. In the Mer Bleue bog community, belowground biomass also exceeded aboveground biomass. Areas with deeper water tables had higher above- and belowground biomass and belowground production, deeper root depths, higher stem: leaf biomass and above-: belowground biomass ratios, and lower aboveground biomass: belowground production. Root decomposition declined with increasing soil depth, particularly below the mean growing season water table level. Long-term water table drawdown in the Finnish bog did not affect total root production as a result of a significant increase in tree root production at the expense of declines in herb root production. Fertilization effects on root biomass at Mer Bleue Bog were limited, with only one of the six treatments showing any effect. Small root (0.5--1 mm diameter) biomass was significantly higher in the top 10 cm of NPK plots fertilized at 10 times the ambient deposition rates relative to the controls. Overall, strong relationships between above- and belowground biomass components suggest that allometric relationships can be developed to estimate belowground biomass and production in these dwarf shrub plant communities. An expanded set of research sites that focuses on belowground processes is necessary in order to gain a better understanding of the environmental and biological aspects that drive root processes in these systems.;My research began by evaluating relationships between above- and belowground biomass and production in a review of wetland plant communities and determining the effect of vegetation type and environmental and climate factors on these relationships within and among wetland types, including peatlands. My subsequent research focused specifically on bog plant communities in Canada and Finland, and the relationships between belowground biomass and production and aboveground biomass as they relate to variations in water table, a key environmental driver within a bog site. Root decomposition rates, a crucial process determining root contributions to soil organic matter, were also studied for the two main evergreen and deciduous shrub species as they relate to root size and soil depth using the litterbag method. The final component of my research evaluated the response of root production and root biomass to long-term water table drawdown and fertilization, respectively, as they relate to aboveground biomass. Root production was estimated using in-growth cores and root biomass was sampled using soil coring.