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CASMGS Insider
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Task 1, Subtask 2: Soil Aggregation, Organic Chemistry, and Microbial Community Composition, Divers |
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SOC constitutes an important global reservoir of carbon (C), accounting for about two times the amount of C tied up in atmospheric CO2 and representing two-thirds of the SOC present in the terrestrial biosphere. As atmospheric levels of CO2 increase steadily due to industrialization, the ability of terrestrial systems to assimilate this increasing burden of CO2 is critically linked to the amount of C sequestered in soils and to the rate that living terrestrial biomass is converted to and sequestered as soil C. Moreover, the rate at which this sequestered C is returned to the atmosphere, either as CO2 or CH4, is intimately linked to its bioavailability and the oxidation process. The bioavailability of C is determined both by its chemical composition and its physical location within the soil matrix. While much is known of the general composition of SOC, the specific structural characterization of SOC has proved a formidable task. Similarly, the importance of soil structure (i.e. physical protection) in determining C dynamics has received considerable recent attention; however, the link between and the relative importance of physical protection versus structural composition is largely unknown. In addition, the influence of microbial community structure/diversity on the oxidation rate of C and the interactions between microbial community structure/diversity, SOC structural composition, and physical protection warrant further study. We have organized a research team in Group B with expertise in soil chemistry, molecular soil organic matter characterization, stable isotope geochemistry, soil mineralogy, soil biophysics, soil structure and physical fractionation, and microbial community characterization. The institutions participating in this Group are CSU, OSU, PU, MSU, KSU, MTSU, PNNL and UNL. This collaboration provides a unique opportunity to link several research approaches to the study of SOC dynamics that have, in the past, often been undertaken independently of one another. The benefits of linking across universities within CASMGS is that each institution maintains long-term agricultural field experiments, and each has unique and complementary expertise in state-of-the-art methodologies relevant to C sequestration research. Linking across institutions will ensure a uniformity of approach, as well as technology transfer, ensuring meaningful comparisons and outcomes.
The primary goal of subtask 2 is to elucidate the biological, chemical, and physical mechanisms controlling the long-term storage of carbon in agricultural soils. Specific objectives are to: •Investigate the role of soil structure (aggregation) on the sequestration of SOC. •Determine the locations of plant and microbial-derived soil organic matter constituents within soil aggregates. •Quantify rates of turnover of specific biomolecules characteristic of plant and microbial origin within SOC and characterize the rate-limiting steps in the C stabilization process •Determine growth yield efficiency and substrate partitioning and relate them to field determined 13C sequestration under different cropping/tillage systems at different sites. •Investigate how microbial community structure, diversity and activity influence C turnover and stabilization. Four sites have been selected for an across-site comparison of aggregation, SOC structural composition, and microbial community characterization. The sites are Wooster, OH; Konza Prairie, KS; Mead, NE; and Sterling, CO. These were selected to represent the major cropping systems in the US (continuous corn, corn-soybean, wheat-fallow), and to include irrigated cropland (Mead, NE) and rangeland (Konza). We will sample a tillage comparison experiment (no-tillage versus conventional tillage) with a continuous corn rotation at Wooster, burned and unburned range plots at Konza, irrigated and rain fed corn-soybean plots at Mead, and wheat-fallow and wheat-corn-fallow plots at Sterling. We estimate that we will process 43 whole soil samples and 215 aggregate fractions. Sample collection will occur in Spring 2002. Six intact soil cores will be collected from each replicate plot to a depth of 20 cm and divided into two depth increments (0-5 and 5-20 cm). The soils will be carefully sieved (8 mm) to avoid aggregate disruption and the six cores from each plot and depth increment will be bulked. Subsamples for whole soil analyses will be shipped immediately on ice to each participating institution. Microbiological analyses will begin within 72 hr of sampling. Additional soil will be sent to CSU for aggregate fractionation and to MSU for separations of aggregates into concentric layers (peeling). The isolated aggregate fractions will then be sent to each participating laboratory for the aggregate analyses. Participants:
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