PARENT SESSION
Oral Session #40: Carbon sequestration and flux.
Presiding: G. Koch
Tuesday, August 6. 1:00 PM to 4:45 PM. Gila Meeting Room, TCC.

Role of resistant fractions in soil C sequestration.

MORRIS, SHERRI^*,1, LEAVITT, STEVEN², GREGORICH, ED³, PAUL, ELDOR⁴, ¹ Bradley University, Peoria, IL² University of Arizona, Tucson, AZ³ Agriculture Canada, Ottawa, Ontario, Canada⁴ Colorado State University, Fort Collins, CO

ABSTRACT- Mitigation for the effects of elevated CO₂ on global change can be achieved through use of terrestrial C sinks. Afforestation of agricultural lands provides both above and belowground C sinks, with as much as 30% of the C sequestered in the soil. Our research evaluates the role of active, slow and resistant fractions in C sequestration. Three sites containing current agriculture and native and afforested deciduous forests on the same soil type were selected for study. Silt loam and sandy textured soils in Ohio, and sandy loam soil in Canada were analyzed for organic C pool dynamics. Active and slow C pools were measured by long-term incubations and resistant pools by acid hydrolysis and ¹⁴C dating. Long-term incubations (300 days) showed significant differences in CO₂ accumulation in all horizons. The active fraction represented less than 5-10% of total soil C for A horizons and 1-5% for lower horizons. The resistant fractions represented approximately 43% of soil organic C in the A horizon and 36% in lower horizons across sites and ranged in ¹⁴C ages from 38 to 368 yrs in the A horizon to 1031 to 4861 years in the lower horizons. The slow and resistant fractions of soil organic C have the potential to provide long-term storage for atmospheric C and should be included in global change models and decision-making for mitigation of elevated CO₂.

KEY WORDS: C sequestration, resistant fractions, afforestation