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Title: ELEVATED CARBON DIOXIDE (FACE) AND IRRIGATION EFFECTS ON WATER STABLE AGGREGATES IN AN AGRICULTURAL SORGHUM FIELD: A POSSIBLE ROLE FOR ARBUSCULAR MYCORRHIZAL FUNGI

Author
item RILLIG, MATTHIAS - UNIV. OF MONTANA
item Wright, Sara
item KIMBALL, BRUCE - USDA PHOENIX, ARIZONA
item PINTER, PAUL - USDA PHOENIX, ARIZONA
item WALL, GARY - USDA PHOENIX, ARIZONA
item ADAM, NEAL - USDA PHOENIX, ARIZONA
item LAMORTE, ROBERT - USDA PHOENIX, ARIZONA
item OTTMAN, MICHAEL - UNIV. OF ARIZONA, TUCSON
item LEAVITT, STEVE - UNIV. OF ARIZONA, TUCSON
item MATTHIAS, ALLAN - UNIV. OF ARIZONA, TUCSON

Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/14/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Increases in atmospheric carbon dioxide highlight the need to explore ways to trap and sequester this greenhouse gas in terrestrial ecosystems. Plants allocate a part of fixed carbon to roots and soil. Organic carbon in soil plays an important role in soil aggregation. Soil aggregates are groups of primary particles that adhere to each other more strongly than to surrounding soil particles. Within soil aggregates, addition carbon is sequestered sometimes for over 400 years. Aggregates are maintained by the presence of biological glues. Increased atmospheric carbon dioxide leads to greater allocation of carbon to plant roots, and this leads to an increase in glue produced by a group of symbiotic root fungi. The glue is glomalin and is produced by arbuscular mycorrhizal fungi. This study shows that glomalin and other measures of arbuscular mycorrhizae activity are related to aggregate stability in an agricultural sorghum field. This information, along with studies of other terrestrial ecosystems that relate glomalin production to increases in aggregate stability, will be used to show that carbon sequestration by soils is manageable.

Technical Abstract: While soil biota and processes are becoming increasingly appreciated as important parameters to consider in global change studies, the fundamental characteristic of soil structure is a neglected area of research. In a sorghum [Sorghum bicolor (L.) Moench] field experiment in which CO2 [supplied using free-air CO2 enrichment (FACE) technology] was crossed factorially with an irrigation treatment, soil aggregate (1-2 mm) water stability increased in response to elevated CO2. Aggregate water stability was increased by 40% and 20% in response to CO2, at ample and limited water supply treatments, respectively. There was no significant effect of water supply itself on soil aggregate stability. Soil hyphal lengths of arbuscular mycorrhizal fungi (AMF) increased strongly in response to CO2, and the concentrations of one fraction (easily extractable glomalin, EEG) of the AMF-produced protein glomalin were also increased. Two fractions of glomalin, and AMF hyphal lengths were all positively correlated with soil aggregate water stability. Our results further support the hypothesis that AMF can become important in global change scenarios via their effects on soil structure. This could be of great importance in agricultural systems threatened by erosional soil loss.