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Harvard Forest Symposium Abstract 2011

  • Title: Response of fine root respiration and biomass to soil warming in hardwood forests
  • Primary Author: Andrew Burton (Michigan Technological University)
  • Additional Authors: Sarah Butler (Marine Biological Laboratory); Jerry Melillo (Marine Biological Laboratory)
  • Abstract:

    Soil warming typically causes large initial increases in soil respiration, with the enhancement lessening over time. This transient response is often attributed to rapid decomposition of labile soil C compounds in the first years of heating, but the potential role of changes in root respiration is not well understood. To assess the degree to which root respiration adjusts to soil warming, specific root respiration rates (nmol CO2/g/s) were measured in a long-term warming experiment at Harvard Forest initiated in 2003. On fourteen dates between September 2007 and May 2010, respiration rates were assessed for fine roots (< 1 mm) from the top 10 cm of control and heated (+ 5 degrees C) 30 m x 30 m plots. Measurements were made at both a reference temperature of 18 degrees C and at the ambient soil temperature of the control or heated treatment on that day.



    Averaged across all measurement dates, fine root respiration rates at the constant reference temperature of 18 degrees C were 17% higher for the heated plot than the control plot (Figure 1A). As a result, specific root respiration rates at ambient soil temperature for the heated plot were significantly higher than for the control for all measurements (Figure 1B), often by more than would be predicted for the 5 degrees C warmer conditions using typical Q10s for root respiration of 2 to 3. Higher fine root metabolic capacity (rate at the 18 degrees C reference temperature) for fine roots from the heated plot were accompanied by higher root N concentrations. However, differences in N concentration did not fully explain differences in metabolic capacity, as respiration rates per unit N tended to be lower for the heated plot than for the control plot (Figure 2), suggesting that a common relationship between fine root N and respiration can not be applied to both treatments.



    The average biomass of roots sorted from soil cores from the heated plot for this study was 48% less than that obtained from the control plot, providing evidence of a large change in fine root biomass in response to soil heating. When this biomass data is used in conjunction with specific respiration rates, the resulting estimates of ecosystem fine root respiration rates are often similar for the control and heated plots (Figure 3). A more detailed sampling conducted on the plots suggests the actual reduction in root biomass is even greater. Overall, the data showed no evidence for acclimation of root respiratory capacity (i.e. lower respiration rates at the reference temperature) in response to warming, with higher rates in the heated plots more common than lower rates. Observations made during fine root sampling indicated instead that reduced root biomass is the key response to warming that is regulating ecosystem root respiration.

  • Research Category: Large Experiments and Permanent Plot Studies

  • Figures:
  • F:WarmingProjectHarvardForestHF2007-2008HarvardForest-Burton2011Abstract-Figure1.pdf
    F:WarmingProjectHarvardForestHF2007-2008HarvardForest-Burton2011Abstract-Figure2.pdf
    F:WarmingProjectHarvardForestHF2007-2008HarvardForest-Burton2011Abstract-Figure3.jpg