Peatland biogeochemistry and plant productivity responses to field-based hydrological and temperature simulations of climate change.

摘要

Northern peatlands have accumulated approximately one third of all soil carbon (C) and therefore play an important role in the global C cycle. Besides the C sink function, peatlands are one of the largest biological sources of atmospheric methane (CH4) and represent approximately 10% of global soil nitrogen (N) stocks. These ecosystems are present at latitudes that are predicted to be highly sensitive to climate change that will likely result in deeper water table positions. The reduction in soil moisture may increase peat decomposition rates and consequently affect nutrient dynamics. While attempts have been made to assess the impact of climate change on peatland C gas exchange and nutrient dynamics, controlled field experimentation remains limited. Therefore, the objectives of this thesis were to estimate the responses of peatland carbon dioxide (CO2) and CH4 flux, nutrient dynamics, and plant productivity to a recent- and a ten-year old drainage, and a warming treatment induced by opentop chambers, across the peatland's hummock-hollow microtopography. The study was carried out at a dry continental treed bog in boreal Alberta during 2011-2013.;Water level drawdown in the longer-term resulted in shifts in biomass coverage and plant community composition between the microforms. The moss biomass was replaced by vascular plant biomass (mostly woody shrubs) at hummocks, and by lichen biomass at hollows. The shift in dominant vegetation was reflected in CO2 fluxes; the longer-term drained hummocks were the largest sink of CO2 while hollows at the same site were the largest sources. While the short- and longer-term drained sites were net sources of CO 2, the warming treatment converted the longerterm drained site to a sink of CO2-C. Water table drawdown greatly reduced CH4 flux at both hummocks and hollows, and the reduction increased with time. The warming treatment increased emissions of CH4 at hollows and increased consumption of CH4 at hummocks. The extractable and available nutrient pools in the peat soil increased with deepening of water level, and over time. The water level driven dynamics of peat nutrient pools were reflected in the vegetation C:N ratio. The warming treatment increased nutrient pools more at hummocks than at hollows and the impact increased with time. Based on these results, I suggest that, models of peatland development need to include C and nutrient cycling links to moisture and temperature parameters to better predict plant productivity and C exchange under changing climatic conditions.