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Harvard Forest Symposium Abstract 2010

  • Title: Response of fine root respiration rates and root N 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. Much of this transient response has been 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 warmer soil temperature regimes, specific root respiration rates (nmol CO2/g/s) were measured in two long-term soil warming experiments at Harvard Forest in September, 2007, six times from May through October, 2008 and five times from June through November, 2009. Soils in the two experiments had been heated since 1991 (6 m x 6 m plots) and 2003 (30 m x 30 m “mega” plots). On each measurement date, respiration rates for fine roots (< 1 mm) from control and heated plots were measured both at a reference temperature of 18 degree C and at the ambient soil temperature of the control or heated (+ 5 degree C) plots on that day.

    Averaged across all measurement dates, fine root respiration rates at the constant reference temperature of 18 degree C were similar for control and heated plots for the 1991 warming experiment and 20% higher for the heated mega plot from the 2003 warming experiment (Figure 1). As a result, respiration rates at ambient soil temperature for these experiments were higher for the heated plots throughout the year (Figure 2), and for the 2003 mega plot warming were often more elevated for the 5 degree C warmer conditions than would be predicted using typical Q10s for root respiration of 2 to 3. Higher fine root metabolic capacity (rate at the 18 degree C reference temperature) for fine roots from the mega plots were accompanied by higher root N concentrations. However, differences in N concentration did not fully explain differences in metabolic capacity. Respiration rates per unit N tended to be lower for the heated plots than for the control plots for both experiments (Figure 3), suggesting that a common relationship between fine root N and respiration can not be applied to both treatments.

    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 in the two experiments, with higher rates in the heated plots more common than lower rates. Other research at the sites, exploring the effects of warming on fine root biomass, will be utilized in conjunction with the specific respiration rates to assess how the two factors combine to regulate ecosystem level responses of root respiration to soil warming. Field observations made during fine root sampling suggest reduced root biomass may play an important role in regulating annual ecosystem root respiration, especially in the mega plots.

  • Research Category: Large Experiments and Permanent Plot Studies

  • Figures:
  • E:WarmingProjectHarvardForestHF2007-2008HarvardForest-Burton2010Abstract-Figure1.jpg