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Soil aggregation and organic matter quality: effects on carbon turnover in eleven ecosystems along a management intensity gradient.
Grandy, A. Stuart*,1,2, Roberston, G. Philip1,2, 1 Michigan State University, East Lansing, MI2 WK Kellogg Biological Station, Hickory Corners, MI
ABSTRACT- Changes in soil aggregation may have important consequences for the capacity of terrestrial ecosystems to sequester carbon and mitigate greenhouse gas accumulation in the atmosphere. We tested whether the interacting effects of vegetation and soil disturbance on aggregation and organic matter quality could explain soil C concentrations in eleven ecosystems in southwest Michigan. The ecosystems represent a management intensity gradient and contain soil carbon levels ranging from 1.0 (a conventionally managed corn-soybean-wheat rotation) to 3.6% (midsuccesional community). Large aggregates (2-8 mm) as a percentage of the soil weight varied from 20% in the conventionally managed field crop rotation to 50% in an old-field successional community. Large aggregate levels associated with no-till agriculture (alfalfa: 33%; field crop rotation: 32%) demonstrated the degradative effects of tillage; aggregation in an organic field crop rotation that includes a cover crop (29%) and in several different successional communities (27-50%) highlighted the importance of plant community composition. Data are consistent with the hypothesis that soil aggregation protects soil organic matter and that aggregation is related not just to soil disturbance but also to plant community characteristics. We use respiration rates of crushed and intact aggregates in three size classes together with inter- and intra-aggregate light fraction organic matter isolation to infer management intensity effects on the mechanisms controlling C cycling.
KEY WORDS: carbon, soil organic matter, aggregation, disturbance