Topsoil Carbon Stock and Soil Physicochemical Properties in Riparian Forests and Agricultural Lands of Southwestern Iran

— This study aimed to evaluate subsoil carbon stock in different stands of riparian forests. Four different sites in the studied riparian forests located in Behbahan in southern Iran, pure Populus euphratica , Tamarix arceuthoides stands, and mixed T. arceuthoides - P. euphratica stands as well as agricultural lands were examined. One hundred and three soil samples were randomly taken at depths of 0–20 cm from all studied sites. Soil carbon content and the physiochemical properties pH, organic carbon, nitrogen, phosphorus, potassium, calcium carbonate, bulk density, and soil texture were determined in the laboratory. The results indicated that soil carbon stocks reach 52.9, 48.5, 25.9, and 25.8 t ha –1 in P. euphratica stands, agricultural lands, mixed T. arceuthoides - P. euphratica stands, and T. arceuthoides stands, respectively. There was no significant difference in soil carbon content between the P. euphratica stands and agricultural lands, but there was a significant difference between T. arceuthoides stands and mixed T. arceuthoides - P. euphratica stands. The high soil carbon content in agricultural lands was probably because of alfalfa and the use of organic fertilizer, like manure, because alfalfa was planted in most of the agricultural lands, and this plant species can store atmospheric nitrogen and, consequently, increase the carbon content in the soil. Furthermore, greater soil biological activity in the P. euphratica stands compared with the T. arceuthoides stands might be responsible for the higher soil carbon content in the P. euphratica stands. The physiochemical properties of soil also play important roles in soil carbon content, the most important of which are soil organic carbon, bulk density, and clay, respectively.