Soil organic matter fractions and aggregate distribution in response to plant community changes

Abstract. Vegetation type is one of the most relevant pedogenic factors controlling soil organic carbon. We determined the influence of vegetation composition on the soil organic carbon in three different plant communities. Three dominant plant communities were selected in grassland habitats in north-western Iran. To compare the soil organic matter (SOM) parameters, soil samples from each community were collected from depths of 0-15cm and 15-30cm. The results showed that the spatial variation of SOM was probably affected by the plant community composition. The highest values of total C occurred in Astragalus microcephalus and Pterpyrum aucheri communities. Total N, POM-C and also POM-N were generally highest in the Astragalus microcephalus community. POM-N contents in both soil depths of the Astragalus microcephalus and Pterpyrum aucheri communities were significantly higher than the Prangus uloptera community. There was a significantly smaller proportion of soil present as macro-aggregates in the upper soil layer of the Astragalus microcephalus community compared to the other communities. There was also a significantly higher proportion of soil present as micro-aggregates in the upper soil layer in the Astragalus microcephalus and Prangus uloptera communities compared to Pterpyrum aucheri. There was no significant difference between micro- and macro- aggregates in the lower soil layer between plant communities. We suggest that, in conservation projects based on higher carbon sequestration, managers should identify the plant communities which can add higher carbon contents to soil and try to extend such communities.