Root and Mycorrhizal Respiration at Harvard Forest Soil Warming Experiments since 2007

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 and mycorrhizal 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) are being measured in three soil warming experiments at Harvard Forest. Soils in the experiments had been heated since 1991, 2003 and 2006. Respiration rates for fine roots (less than 1 mm) from control and heated plots were measured both at a common reference temperature of 18 deg C and at the ambient soil temperature of the measurement date for the control and heated (+ 5 deg C) treatments. Mycorrhizal respiration is being assessed through the use of hyphal ingrowth bags which allow determination both mycorrhizal hyphal biomass and respiration rate. Changes in mycorrhizal community composition are also being investigated. Specific questions we will address include: Does rapid temperature acclimation occur in roots of large perennial woody plants? How do root biomass, root N concentration, and root respiration rates adjust to long-term changes in soil temperature and moisture and concomitant changes in N availability? How is mycorrhizal biomass and activity influenced by the effects of warmer soil temperatures on host C balance and soil N availability? How do the short- and long-term responses of roots and mycorrhizae to warming and associated changes in soil nutrient cycling affect soil CO2 efflux and C availability for aboveground NPP? Are the interrelationships between warmer soil temperature regimes and C fluxes to and from roots and mycorrhizae adequately described by current ecophysiological models?