Exploring the Role of Arbuscular Mycorrhizal Fungi in Carbon Sequestration in Agricultural Soil [GRACEnet].

Sequestering carbon in agricultural soils is a possible mechanism of mitigating increases in atmospheric greenhouse gases.  Work at The Rodale Institute’s Farming Systems Trial® indicates significant potential for carbon sequestration in organically farmed soils.  A potential mechanism for this is C storage in the form of the arbuscular mycorrhizal [AM] fungus produced glycoprotein glomalin, a compound that plays a role in stabilizing soil aggregates and is resistant to degradation.  A two year study was initiated in 2006 utilizing three farming systems: conventional, organic with animal manure addition, and organic with legume cover crops.  Soil samples were collected to a depth of 80 cm on Nov. 29, 2006 and Nov. 1, 2007 following corn (Zea mays) harvests.  Samples were segmented by soil profile depth and analyzed for AM fungi, glomalin, soil C and organic matter, and water stable soil aggregates.  Bulk density for each FS x depth combination was determined on the 2007 samples.  The organic rotations had more propagules of AM fungi in the top 20 cm of soil than the conventional rotation.  Propagules were nearly absent at the 60-80 cm depth in all systems.  Soil carbon in the top 20 cm was significantly greater in the manure (2.59%) and legume (2.41%) based organic systems than in the conventional system (1.79%), but was similar in all systems below that depth.  The organic systems tended to sequester more carbon through the 30 cm depth than the conventional, with sequestration below 30cm equal among the three systems.  Carbon sequestration in the organic systems, over and above that of the conventional, averaged 367 and 460 Kg ha^-1 yr^-1 for the legume and manure systems, respectively.  Glomalin and water stable soil aggregation also will be presented and correlated to AM fungi and soil carbon data.