A comparison of heterotrophic soil respiration versus total soil CO2 efflux and eddy-covariance based whole ecosystem respiration in a mid-latitude deciduous forest

The single largest component in the calculation of net CO₂ flux from mid-latitude deciduous forests is the flux from forest floor and soil respiration; however, accurate measurements and partitioning of this flux into heterotrophic and autotrophic components are difficult.  In recent years, there has been increased interest in measuring and modeling soil respiration as various ecosystem-level carbon dynamics studies have continued to identify the importance of this flux.  Estimates of seasonal soil respiration rates for 2005 made by direct measurement using an automated chamber system in trenched (heterotrophic only respiration) and untrenched (total soil CO₂ efflux) plots are compared with estimates of whole ecosystem respiration generated by eddy covariance flux measures.  This research was conducted at the AmeriFlux site in the Morgan-Monroe State Forest (MMSF).  MMSF is predominately secondary successional broadleaf forest.  There are a wide variety of tree species present in this region, as it is located within the transition zone between the maple-beech and oak-hickory associations of the Eastern Deciduous Forest.  We estimate an annual partitioning ratio for heterotrophic versus autotrophic respiration to be ~1:1.  Estimates of total ecosystem respiration by the flux tower are consistently lower than estimates of total soil CO₂ efflux though these should be higher during the growing season.  However, trenched, untrenched and whole ecosystem respiration measurements were similar during the non-growing season, as expected.