Glomalin in soil aggregates under different forest and pasture systems in the North of Rio de Janeiro state, Brazil

Abstract Reforestation with forest legumes associated with nitrogen-fixing bacteria and arbuscular mycorrhizal fungi has been shown to be a favorable technique for revegetating degraded soils. This study was conducted with soils under forest legume plantations, secondary forest and pasture. Soil protein related to glomalin (SPRG) production and the organic C and total N accumulation were quantified in whole soils and in aggregate-size fractions. Structural equation modeling was used to test relational models between SPRG, C and N levels in whole soil and aggregate-size fractions. A principal component analysis (PCA) was performed to assess the dissimilarity between vegetation covers. The present study sought to answer the following questions: Do legume plantations favor SPRG production and consequently C and N accumulation in the whole soil and in the aggregate-size fractions?; and 2) Are SPRG concentrations directly related to the C and N levels of soils and aggregate size-fractions? The structural model of the whole soil pointed out that the number of spores had a direct and weaker effect on glomalin, but a direct and relatively strong effect on OM accumulation. The models of fractions > 2.00 mm and macroaggregates showed that glomalin had a direct and strong effect on OM accumulation in these fractions. However, the relationship in the fraction > 2.00 mm was positive, and the OM accumulation in the macroaggregates was at the expense of glomalin. In turn, the PCA highlighted that all the analyzed SPRG did not explain much of the dissimilarities between the vegetation covers.