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Harvard Forest REU Symposium Abstract 2016

• Title: Explaining Thermal Acclimation of Soil Respiration in Response to Prolonged Soil Warming
• Author: Catherine A Polik (Harvard University)
• Abstract:

  Soil organic matter (SOM) is the largest organic carbon reservoir in land ecosystems. The warming climate has the potential to accelerate SOM decay through increased microbial respiration, releasing more carbon dioxide into the atmosphere. At the Prospect Hill Soil Warming Experiment, plots have been heated to 5° C above ambient soil temperature for the last 25 years. Despite increases in annual carbon fluxes from the soil, at any given temperature the heated soils were respiring less than the control soils. This response has been termed thermal acclimation. To explore this further we incubated soils by horizon (surface organic and upper mineral) from the heated and control plots at a range of temperatures and measured how this affected heterotrophic respiration rates. The respiration patterns seen in the incubation matched the field data. Heated soils respired less, but also had less SOM and lower microbial biomass than control soils. When scaled by SOM, the acclimation response disappeared in the organic horizon, but remained in the mineral horizon. Scaling microbial biomass by SOM also provided similar values across treatments in the organic horizon, but lower values in the heated plot for the mineral horizon. Thus, scaling respiration by biomass removed the acclimation response in both horizons. We later added sucrose to release the microbes from substrate limitation, but the acclimation response persisted. Therefore, microbial biomass is the key to explaining the acclimation. These results are integral to modeling the response of soil carbon to warming and potential self-reinforcing feedbacks to the climate system.

• Research Category: Forest-Atmosphere Exchange; Large Experiments and Permanent Plot Studies; Soil Carbon and Nitrogen Dynamics