A SURVEY OF SOILS FOR AGGREGATE STABILITY AND GLOMALIN, A GLYCOPROTEIN PRODUCED BY HYPHAE OF ARBUSCULAR MYCORRHIZAL FUNGI

Understanding the contributions of soil microorganisms to soil stabili zation at the molecular level will lead to ways to enhance inputs for sustainable agricultural systems. Recent discoveries of copious produc tion of glycoprotein (glomalin) by arbuscular mycorrhizal (AM) fungi a nd the apparent recalcitrance of this material in soils led to the com parison between concentration of glomalin and aggregate stability. Sta bility was measured on air-dried aggregates rewetted by capillary acti on and then subjected to wet sieving for 10 min. Thirty-seven samples from four geographic areas of the U.S. and one area of Scotland were t ested. The monoclonal antibody used to discover glomalin on AM hyphae was employed to assess immunoreactive glomalin on aggregate surfaces b y immunofluorescence and in extracts from aggregates by enzyme-linked immunosorbent assay (ELISA). Immunofluorescence was observed on at lea st some surfaces of aggregates from all soils examined, but was most e vident on aggregates with high glomalin concentrations. Easily extract able glomalin (EEG) was solubilized by 20 mM citrate, pH 7.0 at 121 de grees C for 30 min, and total glomalin (TG) was solubilized with 50 mM citrate, pH 8.0 at 121 degrees C for 90 to 450 min. Some soils requir ed up to seven sequential extractions to remove all of the glomalin. A ggregate stability was linearly correlated (p < 0.001) with all measur es of glomalin (mg/g of aggregates) in these soils. The best predictor of aggregate stability (AS) was immunoreactive easily extractable glo malin (IREEG) according to the following relationship: AS = 42.7 +61.3 x log(10) IREEG (r(2) = 0.86; p < 0.001, n = 37).