Sources of Below-Ground Respired Carbon in a Northern Minnesota Ombrotrophic Spruce Bog and the Influence of Heating Manipulations.

Abstract:

A significant uncertainty in future land-surface carbon budgets is the response of wetlands to climate change. A related question is the future net climate (radiative) forcing impact due to ecosystem and environmental change in wetlands. Active wetlands emit both CO₂ and CH₄ to the atmosphere. CH₄ is, over a few decades, a much more potent greenhouse gas than CO₂ whereas as a consequence of a much longer atmospheric lifetime, CO₂ has a longer ‘tail’ to its influence. Whether wetlands are a net source or sink of atmospheric carbon under future climate change will depend on the response of the ecosystem to rising temperatures and elevated CO₂. The largest uncertainty in future wetland budgets, and its climate forcing, is the stability of the large belowground carbon stocks, often in the form of peat, and the partitioning of CO₂ and CH₄released via ecosystem respiration.

We have characterized the isotopic signatures (^14,13C of CO₂ and CH₄, D-CH₄) of the respired carbon used for the production of CO₂ and CH₄ from the DOE Spruce and Peatland Responses Under Climatic and Environmental Change (SPRUCE) site in the Marcell Experimental Forest, which contains replicated mesocosm manipulations including above/below ground warming and elevated CO₂. Deep warming (1-2 m) was initiated in July of 2014 and above ground heating will be initiated in July 2015. Comparison of the respired CO₂ and CH₄with recently fixed photosynthate, below-ground peat (up to 11,000 years old), and dissolved organic carbon allow us to determine the primary substrates used by the microbial community.

Control and pre-perturbed plots are characterized by the consumption and respiration of recently fixed photosynthate and recent (few years to 15 yr) carbon. Although CH₄ fluxes have begun to respond to deep-heating, the source of carbon remains similar in the control and perturbed plots. Respired CO₂ remains consistent with being sourced from carbon only a few years old. We will present additional data collected in July, August, and September 2015 which will include the combined influence of above and belowground heating.