Soil aggregate stability and 13C CP/MAS-NMR assessment of organic matter in soils influenced by forest wildfires in Çanakkale, Turkey

The impact of forest fire on soil quality is not well appreciated. This study investigated the influences of forest wild fires that occurred 12, 8, 2 years and 2 weeks before the time of sampling on the composition of the forest floor organic matter by comparing total carbon (C) and total nitrogen (TN), composition of organic functional groups as determined by 13C CP/MAS-NMR and soil aggregate stability of unburned and burned forest floor in Çanakkale, Turkey. Fire altered soil organic matter composition and reduced organic C content of surface (0-5 cm) soil. The 13C CP/MAS-NMR analyses confirmed that the forest soils exposed to fires 12, 10 and 2 years before the time of sampling had higher potential for humification than unburned control soils. However, soils exposed to the fire 2 weeks before the time of sampling became more humified than unburned control soils. Carbohydrate contents of the recently burned soils were distinctly lower than those of the control soils. This is expected, as burning would reduce fresh litter which contains labile and easily decomposable materials. There was 20% decrease in 1990, 52% in 1994, 43% in 2000 and 11% in 2002 of soil organic carbon values of burned soils, compared to unburned forest floor. Fire also reduced the stability of soil aggregates by 1-16%. It was found that carbohydrate content of soil organic matter was directly related (r2=0.92) to the stability of soil aggregates but not to the total amount of organic matter. The very high correlation coefficient suggests that carbohydrate C functional group plays an important role in the stabilization of soil aggregates.