Harvard Forest Research

Modeling acclimation of soil respiration to cliamte change in the context of rising CO2, nitrogen deposition, and ozone

Principal Investigator: Benjamin Felzer
Lehigh University: Oct 01 2009 - Oct 01 2011:

Abstract:
Abstract

Project Objectives: We plan to use an integrative model-data approach to demonstrate the effect of warming on root and heterotrophic respiration at the Harvard Forest soil warming sites. We will also use data from the eddy covariance tower for model runs. We will show how different assumptions about acclimation and decomposition rates will affect model projections of the future terrestrial carbon sink. The effects of climate change will be explored with and without increasing CO2, ozone, and nitrogen deposition to examine the impact of these distinct stressors.

Hypotheses: From recent data, we hypothesize that root respiration may acclimate to warmer climate thus reducing its response, while variable rates of decomposition within the soil may result in the appearance of acclimation through slower release of CO2 to the atmosphere. This potential for below-ground respiration to acclimate to a warmer climate leads to great uncertainty in how future respiration rates will increase. Soil respiration is affected by multiple stresses, which raises some key questions. How will acclimation to a warmer climate respond to rising atmospheric CO2 in nitrogen-limited and ozone-damaged forested ecosystems? What are the effects of slower increases in the rates of soil respiration on the terrestrial carbon sink? By answering these questions, we will gain a deeper understanding of how the effect of warming on soil respiration will alter the terrestrial carbon sink within the context of CO2 fertilization, nitrogen limitation, and ozone pollution.

Methods: We propose to refine our Terrestrial Ecosystems Model (TEM) by developing multiple soil physical layers and quality pools to better model soil temperature and moisture, and to allow for variable decomposition rates of soil organic matter. The model will be validated for historical periods using eddy covariance, soil respiration, and root respiration data. We will perform a factorial set of experiments to explore the effects of climate on respiration and decomposition and other experiments to ascertain if and how plant and microbial respiration acclimatize to warmer temperatures, using several SRES future scenarios.

Accomplishments: This research will undertake a data-model synthesis to explore how soil respiration will respond to future warming. We will determine the most appropriate temperature-dependencies for plant and microbial respiration and the degree to which temperature acclimatization needs to be considered. The new model development will be the basis for extrapolation to the Northeast region and future model intercomparison studies and workshops.

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