Influences of storage temperatures and extraction solutions on the determination of glomalin in Paraiban soils

Abstract

Arbuscular mycorrhizal fungi (AMF) produce glomalin, a glycoprotein that contributes to the formation of stable aggregates, to the sequestration of heavy metals and as a pool of C and N in soils. Soil, climate, fungi specie, vegetation type, land use system, and crop management practices influence the amount of glomalin deposited by the AMF. The efficiency of two extraction solutions and the effect of two storage temperature on the amount of glomalin were determined in samples of a Fluvic Neosol and a Luvisol, located in the semi-arid area of Paraiba state, Northeast Brazil. Glomalin contents were quantified soon after sampling and 15 months after storing part of the samples at room temperature (± 25 ºC) or in a refrigerator (± 4 ºC). Quantification was tested with sodium citrate or with sodium pyrophosphate (both at 20 mM, pH 7.0). The samples stored in the refrigerator had up to 47.6% more glomalin that the ones maintained at room temperature. There were no significant differences between the amounts extracted with sodium citrate or with sodium pyrophosphate. It is recommended to refrigerate the soil samples after field collection, to obtain a better quantification of glomalin.