See more from this Division: S07 Forest, Range & Wildland Soils
See more from this Session: General Forest, Range & Wildland Soils: I
Monday, November 1, 2010: 2:45 PM
Long Beach Convention Center, Room 103C, First Floor
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 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-1 s-1) were measured in long-term warming experiments
at Harvard Forest initiated in 1991 and 2003. On twelve dates between September, 2007 and
November, 2009, respiration rates for fine roots (< 1 mm) from control and
heated (+ 5 oC) plots were measured at both a reference temperature
of 18 oC and at the ambient soil temperature of the control or
heated plots. Average fine root
respiration rates at the constant reference temperature of 18 oC
were similar for control and heated plots for the 1991 warming experiment and
20% higher for the 2003 warming experiment.
As a result, respiration rates at ambient soil temperature were higher
for the heated plots throughout the year, and for the 2003 warming experiment
were often more elevated for the 5 oC increase than would be
predicted using typical Q10s for root respiration of 2 to 3. Higher fine root metabolic capacity (rate at
the 18 oC reference temperature) for the 2003 warming treatment was
accompanied by higher root N concentrations.
However, respiration rates per unit N tended to be lower for the heated
plots, 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 specific root respiratory capacity in response to warming, but
field observations made during fine root sampling suggest reductions in root
biomass with warming may play an important role in regulating annual ecosystem
root respiration response.