Progress 12/15/00 to 12/31/03
Outputs
This termination report summarizes work completed on this project while the PI (Frey) was on the faculty at Ohio State University. The work will continue for another two years under a new project number at the University of New Hampshire where the PI is now employed. The overall goal of this project is to quantify bacterial and fungal contributions to soil organic matter formation and stabilization in no-tillage (NT) and conventional tillage (CT) agricultural systems. Field samples were collected during fall 2000 from NT and CT plots at sites in Wooster, OH and Athens, GA to determine where microbial-derived organic matter is located within the soil matrix. The samples were separated into the following aggregate size classes by wet sieving: >2000, 250-2000, 53-350, and <53 microns. The small macroaggregates (250-2000 micron fraction) were further fractionated to isolate coarse particulate organic matter (POM), microaggregates and the silt+clay fraction. These fractions
were analyzed for total C and N, POM-C, and amino sugar concentrations. The results were summarized in an earlier progress report and will be published in a forthcoming publication. We have also measured amino sugar concentrations on archived soil samples collected from thirteen paired NT and CT plots. These soils were previously analyzed for soil moisture, texture, bulk density, pH, total organic C and N, particulate organic matter C and N, and mineralizable C and N. We are using the expanded database (including amino sugars) to examine potential controls on the relative accumulation of bacterial versus fungal-derived cell wall products. Results from this component of the project were also summarized in the earlier report. A manuscript is in preparation and will be submitted for publication in the Soil Science Society of America Journal (see publication section below). During December 2001, we (Frey and Six) worked with colleagues at the University of Bayreuth, Bayreuth, Germany to
develop a method for using stable isotopes (13C) to follow the fate of carbon into bacterial versus fungal cell wall residues. We labeled three soils which varied in clay content with 13C-labeled glucose and incubated in the lab for 30 days. At day 2 and 30 we extracted fungal-derived glucosamine and bacterial-derived muramic acid from the soil and analyzed the isotopic signature of these sugars. We found a significant enrichment in both bacterial and fungal-derived products. We are currently completing an additional analysis of unlabeled soil that is required to accurately interpret our earlier results. Our plans for the coming year include further optimization of the stable isotope procedure and a field experiment during summer 2003 in which we will inject 13C-labeled wheat into adjacent NT and CT plots. We will then extract labeled amino sugars at several sampling times throughout the growing season and examine the relative accumulation of bacterial versus fungal cell wall
materials. The wheat material is currently being labeled and will be ready to apply to the field plots in spring 2003.
Impacts
This research provided new information on the interactions between microbial community composition, soil properties (e.g., texture, aggregation), and carbon storage in no-tillage and conventional tillage soils. The results will provide information relevant to the maintenance of soil fertility and to the development of sustainable agricultural systems that can, through sequestration of soil carbon, help mitigate rising atmospheric carbon dioxide concentrations.
Publications
- Frey, S.D., J. Six and E.T. Elliott. 2002. Decomposer fungi pump litter carbon belowground. Soil Biology & Biochemistry (in review).
- Frey, S.D., T. White-Burford, J. Six and M. Chantigny. 2002. Climate, Texture, and Tillage Effects on Microbial-Derived Amino Sugars in Agroecosystems. Soil Science Society of America Journal (in prep).
- Six, J., S.D. Frey, and R. Thiet. 2002. Bacterial and fungal contributions to carbon sequestration in agroecosystems. Soil Biology & Biochemistry (in review).
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Progress 01/01/01 to 12/31/01
Outputs
The overall goal of this project is to quantify bacterial and fungal contributions to soil organic matter formation and stabilization in no-tillage (NT) and conventional tillage (CT) agricultural systems. Specific objectives are to (1) determine where bacterial and fungal-derived organic matter is located within the soil aggregate structure, (2) examine factors controlling fungal:bacterial biomass ratios and the relative accumulation of bacterial and fungal cell wall products, and (3) examine whether microbial community composition, particularly the relative abundances of bacteria and fungi, influence the overall production and degradation of microbial-derived organic matter. Bacterial and fungal cell wall constituents (muramic acid and glucosamine, respectively) are being measured to quantify the relative contributions that bacteria and fungi make to the formation and stabilization of microbial-derived organic matter. During fall 2000, field samples were collected
from NT and CT plots at sites in Wooster, OH and Athens, GA to determine where microbial-derived organic matter is located within the soil matrix. The samples were separated into the following aggregate size classes by wet sieving: >2000, 250-2000, 53-350, and <53 microns. At both sites we found a higher aggregation level under NT than under CT in the 0-5 cm depth. In the 5-20 cm layer, aggregation was higher under no-tillage at the Wooster site, but not at the Athens site. In the Wooster soil, C content increased with increasing aggregate size whereas there was no difference in carbon content across the three largest size classes in the Athens soil. The small macroaggregates (250-2000 micron fraction) were further fractionated to isolate coarse particulate organic matter (POM), microaggregates and the silt+clay fraction. These fractions are currently being analyzed for total C and N, POM, and amino sugar concentrations. We also measured amino sugar concentrations on archived soil
samples collected from thirteen paired NT and CT plots. These soils were previously analyzed for soil moisture, texture, bulk density, pH, total organic C and N, particulate organic matter C and N, and mineralizable C and N. We are using the expanded database (including amino sugars) to examine potential controls on the relative accumulation of bacterial versus fungal-derived cell wall products. We hypothesized that fungal cell wall products would be relatively more abundant than bacterial cell wall products in NT compared to CT systems because of the relative dominance of fungi in NT systems. However, our results showed a significant increase in glucosamine relative to muramic acid in NT compared to CT at only 2 of the 13 sites sampled. We also predicted that clay content would be a significant factor in determining the relative accumulation of microbial cell wall products within agroecosystems. We found a positive relationship between clay content and the concentrations of both
glucosamine and muramic acid in the NT plots. In the CT soils there was a positive relationship between muramic acid concentration and clay content, but not glucosamine and clay content.
Impacts
Our research will improve our understanding of the linkages between soil microbial communities and carbon cycling by addressing the mechanisms underlying observed patterns in microbial community structure and microbial-derived soil organic matter in agricultural soils.
Publications
- No publications reported this period
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