Source: UNIV OF NEW HAMPSHIRE submitted to NRP
MICROBIAL CONTRIBUTIONS TO CARBON SEQUESTRATION
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
COMPLETE
Funding Source
NRI COMPETITIVE GRANT
Reporting Frequency
Annual
Accession No.
0194545
Grant No.
2001-35107-12975
Cumulative Award Amt.
(N/A)
Proposal No.
2003-01031
Multistate No.
(N/A)
Project Start Date
Jul 1, 2002
Project End Date
Dec 31, 2004
Grant Year
2003
Program Code
[25.0]- (N/A)
Recipient Organization
UNIV OF NEW HAMPSHIRE
(N/A)
DURHAM,NH 03824
Performing Department
(N/A)
Non Technical Summary
There is growing interest in determining to what extent agricultural soils can sequester carbon (C) and thereby serve as one of several mitigation strategies for reducing rates of carbon dioxide accumulation in the atmosphere. There is particular interest in the use of conservation tillage practices, especially no-tillage (NT), to increase soil C storage. Soil C concentrations are ultimately determined by processes occurring at the level of the microbial cell, even though microbial biomass C typically accounts for only 3-5% of the total soil C. Changes in the rates of microbial processes can have an enormous impact at the ecosystem level and ultimately, on the global C budget. Previous work in NT systems indicates that NT soils generally have higher soil C contents, higher fungal:bacterial biomass ratios, greater accumulations of fungal compared to bacterial-derived soil organic matter (SOM), and increased aggregation compared to adjacent conventional tillage (CT) systems. Links between, on the one hand, fungal abundance and aggregation, and on the other hand, aggregation and SOM dynamics have been made. However, little research has been done to examine how tillage-induced shifts in microbial communities influence aggregation and consequently SOM dynamics, particularly the accumulation of soil C. The purpose of the study is to investigate the role of soil microorganisms in the formation and stabilization of soil organic matter in agricultural soils.
Animal Health Component
(N/A)
Research Effort Categories
Basic
100%
Applied
(N/A)
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
10201101070100%
Knowledge Area
102 - Soil, Plant, Water, Nutrient Relationships;

Subject Of Investigation
0110 - Soil;

Field Of Science
1070 - Ecology;
Goals / Objectives
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.
Project Methods
Bacterial and fungal cell wall constituents (muramic acid and glucosamine) are being measured to quantify the relative contributions that bacteria and fungi make to the production and stabilization of microbial-derived soil organic matter (SOM). 13C-labeled substrates (glucose or plant residues) will be used to trace the movement of substrate C into bacterial and fungal products and to examine rates of bacterial versus fungal product decomposition. This research will focus on the interactions between microbial community composition, soil properties (e.g., texture, aggregation), and C stabilization and will provide information relevant to the maintenance of soil fertility and to the development of sustainable agricultural systems that can, through sequestration of soil C, help mitigate rising atmospheric CO2 concentrations.

Progress 07/01/02 to 12/31/04

Outputs
The goal of this work was to examine microbial contributions to soil organic matter formation and stabilization in no-tillage agroecosystems. We published a detailed literature review which summarizes the current knowledge of microbial processes affecting C sequestration in agroecosystems. Additionally, we used a combination of field observations and laboratory experiments to evaluate (1) the effect of reduced tillage on the accumulation of fungal- versus bacterial-derived organic matter within the soil matrix, and (2) whether microbial community composition, particularly the relative abundances of bacteria and fungi, influences the metabolic efficiency of the soil microbial community. We addressed objective 1 by quantifying the amino sugars glucosamine, galactosamine, and muramic acid in aggregate size fractions isolated from no-tillage (NT) and conventional tillage (CT) soil. Intact soil cores (0-5 and 5-20 cm depth) were collected from the long-term tillage experiment at Horseshoe Bend in Athens, Georgia. Four water-stable aggregate size fractions were isolated: large macroaggregates (>2000 microns), small macroaggregates (250-2000 microns), microaggregates (53-250 microns), and the silt+clay fraction (<53 microns). Small macroaggregates were further separated into coarse particulate organic matter, microaggregates contained within macroaggregates, and the silt+clay fraction. Amino sugars were extracted from all fractions, purified, and analyzed by gas chromatography. Fungal-derived amino sugar C (FAS-C) comprised 63%, while bacterial-derived amino sugar C (BAS-C) accounted for 37% of the total amino sugar C pool under both tillage treatments. No-tillage soil contained 21% more amino sugar C than the CT soil across the entire plow layer. Both the % of total organic C as FAS-C and BAS-C were significantly higher in the silt+clay fraction of NT versus CT soil. The % of total organic C as FAS-C was significantly higher in small macroaggregates of NT versus CT soil due to a preferential accumulation of FAS-C in the microaggregates contained within these macroaggregates. These results indicate that microbial-derived C is stabilized in NT soils, due primarily to a greater fungal-mediated improvement of soil structural stability and concurrent deposition of fungal-derived C in microaggregates contained within macroaggregates. To address objective 2, we measured microbial growth yield efficiency in agricultural soils by following 13C-labeled glucose loss and CO2 evolution in two experiments (differing in N amendment levels) in which the fungal:bacterial biomass ratios (F:B) were manipulated. No differences in efficiency were observed for communities with high versus low F:B in soils with or without added inorganic N. Our experiments do not support the widely held assumption that soil fungi have greater growth efficiency than soil bacteria. Thus, claims of greater fungal efficiency may be unsubstantiated and should be evoked cautiously when explaining the mechanisms underlying greater C storage and slower C turnover in fungal-dominated soils.

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. 2003. Reciprocal transfer of carbon and nitrogen by decomposer fungi at the soil-litter interface. Soil Biology & Biochemistry 35, 1001-1004.
  • Simpson, R.T., S.D. Frey, J. Six, and R.K. Thiet. 2004. Preferential accumulation of microbial carbon in aggregate structures of no-tillage soils. Soil Science Society of America Journal 68, 1249-1255.
  • Six, J., S.D. Frey, R.K. Thiet, and K.M. Batten. 2005. Bacterial and fungal contributions to carbon sequestration in agroecosystems. Soil Science Society of America Journal (in press)
  • Thiet, R.K., S.D. Frey, and J. Six. 2005. Growth yield efficiencies of soil microbial communities with different fungal:bacterial ratios. Soil Biology & Biochemistry (in press)
  • Vaisanen, R.K., M.S. Roberts, J.L. Garland, S.D. Frey, and L.A. Dawson. 2005. Physiological and molecular characterization of microbial communities associated with different water-stable aggregate size fractions. Soil Biology & Biochemistry 37, 2007-2016.