This study analyzed the relationship between the vertical distribution of root biomass and soil organic carbon (SOC) content in the arid shrub lands of Semnan province in Iran. Three sites were selected based on differences in canopy cover of Artemisia sieberi (5%, 10% and 15%). Average density of shrubs, root biomass and SOC were determined at different depths (0-20, 20-40, 40-60, 60-80 cm) in 20 quadrats at each site and are expressed on a per ha basis. Simple equations were used to calculate the relationship between SOC and root biomass for each site. Statistical analyses were conducted using ANOVA. The results showed that the root biomass and the SOC content generally decreased as soil depth increased. There was an acceptable relationship between root biomass and SOC at all sites. The proportion of SOC in the soil was found to be positively related to the vertical distribution of root biomass; 75% of total root biomass was found at 0-25 cm, while this same soil layer contained 48% of SOC.
