Northern peatlands historically represent a natural sink for global atmospheric carbon, but it is unclear how peatland carbon balances will respond to changing climate and disturbance regimes. Remote sensing in interior Alaska has shown that major wetland complexes are drying, while permafrost thaw and groundwater upwelling produces flooding due to thermokarst and ground subsidence. Both scenarios have the potential to influence carbon sequestration through changes in factors such as plant succession and resource controls on primary production.  At the Alaskan Peatland Experiment (http://www.uoguelph.ca/Apex), located near the Bonanza Creek Experimental forest, we are examining the effects of water table manipulations in a rich fen, and the effects of permafrost thaw in a black spruce bog. The objective of this presentation will be to examine the responses of gross primary production (GPP) and vascular net primary productivity (NPP) across the APEX sites (rich fen and bog) and treatments (fen: control, drought and flooded plots; black spruce bog: plots in stable permafrost, recent thaw and older thaw).

Results/Conclusions

In the rich fen, there was large inter-annual variability in the understory vascular NPP for both the flooded (raised water table treatment) and drought (lowered water table treatment) plots between harvests from 2007 and 2009, while NPP at the control plot did not vary between years. Understory vascular NPP decreased in the flooded plot relative to the control by more than 50%, and increased in the drought plot relative to the control.  Also during this time period, the drought plot consistently had lower growing season carbon uptake (GPP) than either the control or flooded plots, presumably because of moss responses to altered hydrology. NPP of understory vascular species was 50% lower in the permafrost bog than both thaw ages, with no differences in NPP between older and newer regions of permafrost thaw in the bog. However, GPP was consistently higher in the area of more recent thaw relative to both the older thaw and the intact permafrost bog. Together, these results indicate that new biomass accumulation (NPP) and rates of plant carbon uptake (GPP) in boreal peatlands are very sensitive to changes in both hydrology and permafrost stability, both of which are already being impacted by climate change.