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Harvard Forest Symposium Abstract 2008

• Title: Adjustment of fine root respiration rates to soil warming in hardwood forests
• Primary Author: Andrew Burton (Michigan Technological University)
• Additional Authors: Serita Frey (University of New Hampshire - Main Campus); Jerry Melillo (Marine Biological Laboratory)
• Abstract:

  Soil heating typically causes large initial increases in soil respiration, with the enhancement lessening over time. This transient response is 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-1 s-1) were measured in three soil warming experiments at Harvard Forest in September, 2007. Soils in the experiments had been heated since 1991, 2003 and 2006. Respiration rates for fine roots (< 1 mm) from control and heated plots were measured both at a common reference temperature of 18 oC and at the ambient soil temperature of the measurement date (15 oC for control and 21 oC for heated). Respiration rates at field soil temperature for heated plots were 45% greater than for unheated plots (Figure 1). This enhancement is lower than the 52 to 77% increase that would be predicted by typical Q10's for forest root respiration of 2.0 to 2.6. As a result, respiration rates at the constant reference temperature of 18 oC were significantly lower for the heated plots, by an average of 23% (Figure 2). Root N concentration did not differ among treatments, thus respiration rate per unit N at the reference temperature was significantly lower for roots from heated plots (Figure 3). Lower respiration rates for roots from warmed soils may indicate physiological acclimation to warmer temperatures or may simply be a consequence of drier soils on the heated plots. Soil moisture contents were 11 to 18% lower for the heated plots, with the treatment effect being significant for two of the three experiments. Continued root respiration measurements during the 2008 growing season will help us separate effects of dry soils from true temperature acclimation and assess the combined effects of warmer and drier soils on the contribution of fine roots to growing season soil respiration flux and belowground C allocation.

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


• Figures:
HF2008AbstractFigure1.pdf
HF2008AbstractFigure2.pdf
HF2008AbstractFigure3.pdf