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Tuesday, November 3, 2009
Convention Center, Exhibit Hall BC, Second Floor
Abstract:
We used density fractionation and radiocarbon-based turnover times to assess differences in soil C cycling amongst four eastern deciduous forests of varying climate, soil type and parent materials, and soil ecology. We collected mineral soil from 0-5 cm and 5-15 cm depth at Harvard Forest (HAF) in central Massachusetts, Bartlett Experimental Forest (BEF) in New Hampshire, the University of Michigan Biological Station (UMBS), and Baskett Wildlife Recreation and Education Area in the Missouri Ozarks (MOZ). We fractionated soil samples by density using sodium polytungstate (1.65 g ml-1) into free light (unprotected SOM), occluded light (physically protected SOM), and heavy (mineral-protected) fractions, measured C concentration and radiocarbon in bulk soil and fractions, and used a three-pool steady-state model to determine radiocarbon-based turnover times for fractions.
Northeastern sites, HAF and BEF, had higher bulk soil C (65 and 40 g C kg soil-1, respectively) than MOZ or UMBS (20 and 10 g C kg soil-1). Radiocarbon values (Δ14C) decreased with depth and were lower at northeastern sites than Midwestern sites (36, 8, 113, and 65 ‰ for 0-5 cm at HF, BEF, MOZ, and UMBS, respectively).
Approximately 20% of bulk soil C was recovered in free light fractions and 10% was recovered in occluded light fractions at HAF, BEF, and MOZ. However, at UMBS, the site with the sandiest soil, over one-third of the bulk soil C was recovered in the free light fraction and only 4% was recovered in the occluded light fraction.
Preliminary radiocarbon-based SOM turnover times for the sites suggest that soil carbon pools in all three fractions turn over much more quickly at MOZ, the warmest site, than the other sites. In addition, turnover times for free and occluded light fractions are slower at UMBS and BEF, the coolest sites, than at HAF and MOZ.
Northeastern sites, HAF and BEF, had higher bulk soil C (65 and 40 g C kg soil-1, respectively) than MOZ or UMBS (20 and 10 g C kg soil-1). Radiocarbon values (Δ14C) decreased with depth and were lower at northeastern sites than Midwestern sites (36, 8, 113, and 65 ‰ for 0-5 cm at HF, BEF, MOZ, and UMBS, respectively).
Approximately 20% of bulk soil C was recovered in free light fractions and 10% was recovered in occluded light fractions at HAF, BEF, and MOZ. However, at UMBS, the site with the sandiest soil, over one-third of the bulk soil C was recovered in the free light fraction and only 4% was recovered in the occluded light fraction.
Preliminary radiocarbon-based SOM turnover times for the sites suggest that soil carbon pools in all three fractions turn over much more quickly at MOZ, the warmest site, than the other sites. In addition, turnover times for free and occluded light fractions are slower at UMBS and BEF, the coolest sites, than at HAF and MOZ.
Deeper soil samples have been collected (to 75 cm in some cases). Carbon storage is being determined for all depths and radiocarbon based turnover times for greater than 15 cm depth may be determined in the future.