In January of 2014, we were notified of the acceptance of our proposal for funding, entitled "Changes in Soil Carbon Dynamics in Response to Long-Term Soil Warming - Integration Across Scales from Cells to Ecosystems". This award is for three years of study, and the PIs are Dr. Kristen DeAngelis, Dr. Jeffrey Blanchard (UMass Biology) and Dr. Jerry Melillo (The Ecosystems Center, MBL).
Soils contain an estimated 2,500 Pg carbon (C), about three times as much as in the atmosphere as carbon dioxide and five times as much as in terrestrial vegetation in various organic carbon forms. A substantial fraction of the soil carbon occurs in relatively complex organic compounds, which are resistant to decomposition under current environmental conditions. How the decay of these compounds will change in a warmer world is not clear. A major question in Earth System Science is now: Will global warming accelerate the decomposition of these complex compounds by microorganisms, releasing carbon dioxide, a powerful heat-trapping gas, to the atmosphere, thereby creating a self-reinforcing (positive) feedback to the climate system? Put another way, will warming beget warming, with microorganisms as the central “actors?” The research proposed here will address this question by leveraging an ongoing climate-change experiment in which the soil in field plots has been heated year-round for 21 years. Soil temperatures in the experimental plots have been raised 5 degrees Celsius above ambient temperatures in a deciduous forest stand at the Harvard Forest Long-term Ecological Research (LTER) site in central Massachusetts. Soils from the heated and control plots will be analyzed to evaluate both biogeochemical and microbial mechanisms of altered C cycling with warming on an ecological time scale. This new information will be used to develop a new model of soil organic matter decay so that it represents the soil decay responses to climate change in a more mechanistic and better way.
The overarching hypothesis is that long-term warming enables and accelerates microbially catalyzed decay of stored, recalcitrant soil carbon and in this way leads to a self-reinforcing feedback to the climate system. Measurements to be made include soil respiration in situ, chemical composition of the soil organic matter, as well as extracellular- enzyme potential activity, compound-specific carbon-use efficiency and microbial RNA sequencing in the laboratory. The research products will include times-series data on microbial communities that span two years. This approach will provide new mechanistic understanding of the interactions among temperature, moisture, soil carbon and microbial metabolic functions, as well as provide a rich template for exploring the descriptive and predictive ability of nucleic acid sequences from soil communities.
Data from the field and laboratory research will be used to integrate biogeochemical and microbiological factors into a new process-based model. The new model will be built within the framework of the Community Land Model’s soil organic matter decay module, which we will enrich with the inclusion of microbial dynamics. Our new decay model will explicitly relate microbial biomass, microbial physiology and extracellular enzyme dynamics to the decay of soil organic matter in response to changes in environmental conditions including changes in soil temperature and moisture.