Thilini D. Ranatunga;Zhongqi He;Kamala N. Bhat;Junyan Zhon

College of Sciences, Old Dominion University, Norfolk VA 23529 (USA); Intertek, Allentown PA 18195 (USA;USDA-ARS, Southern Regional Research Center, New Orleans LA 70124 (USA);Department of Biological & Environmental Sciences, Alabama A&M University, Normal AL 35762 (USA);Department of Physics, Chemistry and Mathematics, Alabama A&M University, Normal AL 35762 (USA)

som fractions;thinning;ecosystem;state 1;3c;prescribed burnin

Forest management practices such as prescribed burning and thinning in forest ecosystems may alter the properties of soil organic matter (SOM). In this study, surface soils from field plots in the Bankhead National Forest, Alabama, USA, were used to investigate possible SOM transformations induced by thinning and burning. Elemental analysis and solid-state 13C cross polarization magic angle spinning nuclear magnetic resonance (13C CPMAS NMR) spectroscopy were used to characterize SOM fractions in whole soils, humic substances, and density fractions. Our data revealed that the changes in SOM fractions due to the repeated burning carried out in the forest ecosystem studied were involved mainly with alkyl C, O-alkyl C, and carbohydrate functional groups, implying that most prominent reactions that occurred involved dehydrogenation, de-oxygenation, and decarboxylation. In addition, burning and thinning might have also affected the distribution and composition of free and occluded particulate SOM fractions. The limited structural changes in SOM fractions suggested that low-intensity prescribed fire in the forest ecosystem studied will not create major structural changes in SOM fractions.