Park, E.J. and A.J.M. Smucker
Presented at the All Scientist Meeting (2002-10-04 )
Intra-aggregate respiration of agroecosystem soil aggregates, during solution flow, identifies new mechanisms that control the sequestration of carbon © within soil aggregates. Respiration of soil aggregates were estimated by measuring CO2 evolution during incubation and by determining dissolved oxygen changes in solutions flowing through single aggregates, 6.3-9.5 mm across. Maximum generation of CO2 following rewetting of air dried aggregates were observed at 6 hours and at 20 hours of incubation for Hoytville and Wooster agricultural soils, respectively. Long-term conventional tillage (CT) significantly reduced aggregate porosities by 15%. Consequently, saturated hydraulic conductivity (Ks) through individual aggregates from native forest (NF) soil, 1.6´10-4 cm/sec, was 12-fold greater than the Ks for CT soil aggregates. Water flux rates through NT aggregates were nearly twice those of CT aggregates. Carbon mineralization rates, on the fifth day of incubation, for aggregates from no-till (NT) soils in Hoytville and Wooster were stable at 1.8 and 1.7 mg CO2-C/g soil/hr, nearly 2.8-fold and 3.6-fold greater than those of CT soil aggregates. In contrast, oxygen consumption by interior regions of aggregates from Wooster CT soils, 3.38 m10-4 cm/sec, was 12-fold greater than the Ks for CT soil aggregates. Water flux rates through NT aggregates were nearly twice those of CT aggregates. Carbon mineralization rates, on the fifth day of incubation, for aggregates from no-till (NT) soils in Hoytville and Wooster were stable at 1.8 and 1.7g CO2-C/g soil/hr, nearly 2.8-fold and 3.6-fold greater than those of CT soil aggregates. In contrast, oxygen consumption by interior regions of aggregates from Wooster CT soils, 3.38g O2/g soil/hr, was 2-fold greater than aggregates from NT soils. Our single aggregate flow cell data suggest that DOC could be leached out of soil aggregates by flowing water before being consumed by microorganisms. We are collecting more biogeochemical data for interior regions of aggregates to identify additional domains that contribute to the multiple C sequestration processes within aggregates.
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