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Harvard Forest Symposium Abstract 2011

• Title: Soil warming alters nitrogen cycling in a New England forest: implications for ecosystem function and structure
• Primary Author: Rose Smith (Marine Biological Laboratory)
• Additional Authors: Noelia Aponte (University of Puerto Rico); Frank Bowles (Research Designs); Sarah Butler (Marine Biological Laboratory); Troy Hill (Marine Biological Laboratory); Jennifer Johnson (Marine Biological Laboratory); Heidi Lux (Harvard Forest); Jerry Melillo (Marine Biological Laboratory); Paul Steudler (Marine Biological Laboratory); Chelsea Vario (Dartmouth College)
• Abstract:

  Global climate change is expected to affect terrestrial ecosystems in a variety of ways. Some of the more well-studied effects include the biogeochemical feedbacks to the climate system that can either increase or decrease the atmospheric load of greenhouse gases such as carbon dioxide and nitrous oxide. Less well-studied are the possible relationships among changes in climate, microbial processes and possible shifts in plant community composition. Here we report the results of a seven-year soil warming study that focuses on the linkages among climate change, microbial processes and plant community responses. Over the first eight years of the study, we observed significant changes to the nitrogen cycle with potential consequences for species composition and storage of organic matter. Since the start of the experiment, we have observed a 45% average annual increase in net nitrogen mineralized and a 25% increase in nitrification rates. Analysis of nitrogen isotopes in bulk soil samples shows relative enrichment of 15N in the warmed area, suggesting that microbes are attacking a more stabile pool of organic matter in response to warming. The warming-induced increase in available nitrogen has also resulted in increased relative growth rate and foliar nitrogen content, and enrichment of 15N in foliar tissue of canopy trees. Acer rubrum (red maple) trees have responded the most after 8 years of warming, with the greatest increases in relative growth rates, foliar nitrogen and percent nitrogen resorption in leaves. Quercus rubra (red oak) has the highest nitrate reductase activity, possibly giving it a competitive advantage if warming continues to enhance soil nitrification rates. Our study suggests that, as inorganic nitrogen availability and form continues to shift in response to warming, species-specific nitrogen acquisition and retention strategies may dictate changes in forest composition and feedbacks to climate change.
  
  
  
  

• Research Category: Large Experiments and Permanent Plot Studies
  Soil Carbon and Nitrogen Dynamics