Pool and Dynamics of Soil Carbon after Firing the Semi Steppe Rangelands of Chaharmahal and Bakhtiari

Firing the vegetal coverage of rangelands is one of the human important interferences in natural ecosystems and specially may lead to change in the ecosystem processes such as soil carbon (C) mineralization. The objective of this study was to investigate the impact of fire on soil organic matter distribution and C mineralization in semi-steppe rangeland of Karsanak region in Chaharmahal and Bakhtiari province. Therefore، three rangeland sites affected by fire in three، two and one years prior to this study (i. e. 2008، 2009 and 2010، respectively) were selected. The soil samples were taken from two depths (0-10 cm and 15-25 cm) of each site with 9 replications; the numbers of soil samples for laboratory analysis were 108. Then، the impacts of fire on the Organic matter pool، C mineralization، and C mineralization rate in the whole soil and its fine and coarse aggregates were analyzed statistically using the independent t-test (p≤ 0. 05). The results showed that the soil organic matter pool in the surface layer reduced significantly in 1 and 2 years after fireing. C mineralization in the surface layer decreased significantly just 1 year after firing and the reduction was 22 percent compared with the control site. C mineralization rate in the surface layer increased significantly in 1 and 2 years after fireing، and the increased amounts were 34 and 22 percent compared with the control site، respectively. Furthermore، C mineralization of the macro fraction in the surface and subsurface layers decreased significantly in 1 year after fire. Totally، it was concluded that firing reduced the rate of soil carbon sequestration during the primary years after firing، but by increasing time its negative effects on soil decreased، relatively.