Short-term metabolic response of sugar maple roots to soil warming

Background/Question/Methods

Exponential increases in plant respiration in response to increased temperatures could create a positive feedback loop that decreases carbon allocation to biomass production, and increases the amount of CO₂ returned to the atmosphere. The objective of this study was to see if the fine roots (<1 mm) in an experimentally warmed sugar maple (Acer saccharum Marsh.) dominated northern hardwood forest can metabolically acclimate to increased soil temperatures, avoiding excessive C loss to respiration. Experimental treatments included a control, soil warming (+4° C) by infrared lamps, water addition (130% ambient), and soil warming plus water. The water additions are intended to offset the increased evaporative water loss due to warming. Fine root respiration was measured periodically over two and a half growing seasons with an open-system infrared gas analyzer at both ambient soil temperature and a constant reference temperature of 18° C. Measurements at the reference temperature were used to assess changes in respiratory capacity over time and across treatments.

Results/Conclusions

Measurements made before experimental warming was initiated indicate fine root respiration increases exponentially with soil temperature (Q₁₀ = 2.7), with no acclimation of respiratory capacity to seasonal changes in soil temperature. Measurements of fine root respiration after warming was initiated indicate that no short-term (days to weeks) acclimation has occurred on the plots that receive warming plus water additions when compared to the control plots. Decreased respiration has occurred on the warming only plots when compared to the control plots, but this appears to be associated with drier soil conditions. Further measurements will be taken during the growing season of 2011 to assess the longer-term response of root system metabolic capacity to the warming treatments.