INTEGRATED AGRICULTURAL SYSTEMS FOR THE NORTHERN GREAT PLAINS
Location: Northern Great Plains Research Laboratory
Title: Arbuscular Mycorrhizal Fungi and Glomalin Enhance Carbon Sequestration in Organic Farming Systems
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: May 1, 2009
Publication Date: July 6, 2009
Citation: Nichols, K.A., Douds, D.D., Hepperly, P.R., Seidel, R. 2009. Arbuscular Mycorrhizal Fungi and Glomalin Enhance Carbon Sequestration in Organic Farming Systems. Meeting Abstract.
Interpretive Summary: Utilizing alternative farming practices, the soil may be a sink for atmospheric carbon dioxide as opposed to a source. The Rodale Institute’s Farming Systems Trial® (FST) has been in continuous production since 1981 and provides an ideal site for comparing organic and conventional systems. Previous research showed the carbon levels rose 0.5% in the organic treatments but remained study in the conventional treatments. Research has also indicated higher amounts of arbuscular mycorrhizal (AM) spore populations and propagules in the organic treatments. This three year study will continue measuring AM spore populations and propagules, as well as water stable aggregation (WSA) and glomalin (an AM glycoprotein) levels in these treatments. Percentage carbon in glomalin extracts will be used to measure the proportion of soil organic carbon is represented by glomalin. Preliminary data indicates that AM fungi and glomalin may enhance carbon sequestration in an organic management system directly through production of glomalin and indirectly by the stabilization of soil aggregates.
Atmospheric carbon dioxide concentrations have increased nearly 100 ppm in the last 250 years. Soils may be able to mitigate this by sequestering carbon, but agricultural soils are often a source rather than a sink for carbon. The Rodale Institute’s Farming Systems Trial® (FST), initiated in 1981 to develop economically competitive organic farming systems, showed carbon levels in the organically farmed soils rose to 2.5% while those of the conventionally farmed soil remained at 2.0% over the first 22 years of treatment. In the 1990’s, significantly higher populations of arbuscular mycorrhizal [AM] fungi were present in organic vs. conventionally farmed soil. AM fungi are symbiotic soil fungi which assist the host plant by taking up mineral nutrients and water from the soil and helping the plant resist pathogens. AM fungi also produce glomalin; a glycoprotein that i) helps to stabilize soil aggregates, ii) is resistant to degradation, and iii) may be a significant portion of soil organic carbon. In 2006, a three year study was initiated to analyze soil samples collected to six depths (0-5, 5-10, 10-20, 20-30, 30-60, and 60-80 cm) in the conventional, organic legume-based, and organic manure-based treatments. Each sample was tested for soil carbon and soil organic matter concentrations, spore populations, and total AM propagules using the MPN bioassay. In addition, soil samples were dry sieved to separate out three aggregate size classes (1-2, 0.25-1, and 0.053-0.25 mm) which were weighed to determine the portion of soil in each size class and analyzed for percentage of water stable aggregates and glomalin-related soil protein (GRSP) concentration. Finally, the GRSP extract was analyzed to estimate the amount of carbon in this fraction per sample. In 2007 and 2008, spore and propagule data followed trends similar to analysis in the 1990’s. GRSP values in 2007 and 2008 were about twice as high as those in 2006, but in all years, the data followed similar patterns with higher values in the organic treatments over the conventional treatment. Percentage carbon values in the GRSP extracts indicate GRSP to be a carbon storage sink. All AM parameters (i.e. spore populations, propagule number, and glomalin concentration) and soil C values declined with increasing depth. The data indicate organic farming systems have the potential to enhance carbon sequestration particularly through the beneficial relationship between AM fungi, glomalin, and plant host production.