Models of global environmental change are dependent on accurate predictions of
the processes regulating carbon (C) and nutrient cycling in terrestrial ecosystems.
Currently much research is focused on peatlands since they contain one-third of
the world's soil C stock and therefore alteration to the processes regulating C and
nutrient cycling have the potential to feedback on predicted global climate
change via carbon dioxide (CO2) loss to the atmosphere.
This study examined the climatic/physicochemical factors that regulate biogeochemical cycling in Sphagnum dominated peatlands and whether Sphagnum productivity affects soil decomposition processes under current and
future climate change scenarios. Field surveys of a riparian peatland and a
blanket bog identified a number of climatic and physicochemical factors that
regulate CO2 fluxes and soil enzyme activities. Peatland mesocosm experiments
identified the effect of Sphagnum productivity on net CO2 ecosystem exchange
and soil enzyme activities under current and future climate change scenarios.
From this thesis, the following conclusions could be drawn regarding plant and soil processes in peatland ecosystems: (1) temperature is the major control on CO2 fluxes in peatland ecosystems although shifts in the water table can modify the effect; (2) Sphagnum and soil respiration represent approximately 50% of ecosystem respiration and thus both are important for predicting respiratory
losses from peatlands by global warming; (3) ecosystem respiration showed a
greater sensitivity to temperature (Q10) than estimated gross Sphagnum
photosynthesis suggesting that global warming may lead to the release of CO2
from blanket bogs; (4) elevated CO2 and temperature forced net CO2 sequestration in the short-term that may lead to an increase in the growing
season; (5) the CO2 fertilization effect may be limited by climatic and
physicochemical factors particularly nutrient availability suggesting that in the
long-term global warming may result in net CO2 emission from peatlands; and
(6) under current environmental conditions, Sphagnum productivity did not
appear to affect ex situ measurements of soil decomposition but may affect in
situ soil CO2 respiration. However, an increase in Sphagnum CO2 fixation by
elevated CO2 may increase soil enzyme activities that may feedback on plant and
microbial growth by increasing nutrient availability and affect the C balance of
northern peatland ecosystems in the future.
Overall, the results from this thesis suggest that multiple, interacting factors
will determine the effect of climate change on the C balance of peatlands in the future. Positive feedback mechanisms such as the CO2-plant-enzyme-nutrient
interaction may have important implications for future C storage in these
systems. The magnitude and duration of this indirect enzymic response to
elevated CO2 may be the key to the C balance of peatland ecosystems in the
future. Without this mechanism, global warming will probably lead to the release of stored soil C to the atmosphere as CO2 or DOC from northern peatlands.