Increases In Woody Plant Root Respiration Found with Decreased Water Depth In a Northern Peatland.

Climate change models predict about a 3.5^°C increase in mean annual temperature by 2100 for northern Michigan. This shift in climate has the potential to lower the water table in peatland systems and alter peatland carbon cycling. Root respiration rates can also be influenced by soil moisture and nutrient availability, and their response to changes in these factors as water table depth changes was the focus of research at Seney National Wildlife Refuge in the Upper Peninsula of Michigan. Woody plant root respiration was measured in drained, wet and control plots established in Seney National Wildlife Refuge. The roots were placed in a chamber attached to an infrared gas analyzer to determine specific root respiration rates.  Ecosystem root respiration was calculated as the product of specific respiration rates and root biomass. The wet and control plots were similar in specific root respiration, ecosystem respiration and root biomass, but all three of these variables were much higher for the drained plots.  There was also a species composition shift from leatherleaf (Chamaedaphne calyculata) dominated hummocks in the wet and control plots, to a mixture of leatherleaf, black spruce (Picea mariana) and tamarack (Larix laricina) in the drained plots.  These results indicate that if increased evaporative demand under climate change leads to lower water tables in peatlands, this in turn may increase the amount of soil CO₂ efflux to the atmosphere from root respiration.  This increase would be due to the combined effects of increasing woody plant density and direct effects of warmer temperature on specific respiration rates.  However, this increased soil CO₂ efflux from root respiration is C that was fixed by growing woody vegetation, and thus it does not contribute to these systems potentially becoming net atmospheric C sources, as net woody biomass increment is greater for the drained peatlands.