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Title: Solid-state 13C nuclear magnetic resonance spectroscopic characterization of soil organic matter fractions in a forest ecosystem subjected to prescribed burning and thinning

Author
item RANATUNGA, THILINI - Alabama A & M University
item He, Zhongqi
item BHAT, KAMALA - Alabama A & M University
item ZHONG, JUNYAN - Old Dominion University

Submitted to: Pedosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/2016
Publication Date: 10/23/2017
Citation: Ranatunga, T.D., He, Z., Bhat, K.N., Zhong, J. 2017. Solid-state 13C nuclear magnetic resonance spectroscopic characterization of soil organic matter fractions in a forest ecosystem subjected to prescribed burning and thinning. Pedosphere. 27(5):901-911.

Interpretive Summary: Prescribed burning and thinning are gaining popularity as low-cost forest protection measures. The goal of this study is to obtain information on heat-induced structural modification of soil organic matter (SOM) and distribution of SOM fractions in a Southern Appalachian forest ecosystem subjected to prescribed burning and thinning treatments. Chemical and physical fractionation methods of SOM combined with advanced nuclear spectroscopy were used to investigate structural changes in SOM. Results suggested that certain thermal induced composition changes in SOM fractions could be observed during burning process depends on the fire intensity and the type and quantity of burned or partially burned vegetative cover remaining on the soil surface. Those changes were involved mainly with three types of C functional groups, implied that most prominent reactions occurred during this low-intensity burning process involved dehydrogenation, de-oxygenation, and decarboxylation. The limited structural changes of SOM fractions suggested the prescribed burning and thinning treatments had very low impact on changing composition of organic C forms in the soils studied, indicating that low intensity fire treatments in this ecosystem would not severely affect any structural changes in organic matter forms.

Technical Abstract: Prescribed burning and thinning are gaining popularity as low-cost forest protection measures. Such field management practices could alter the chemical properties of soil organic matter (SOM), especially humic substances. In this work, we collected surface soil samples from the Bankhead National Forest, Alabama, containing field plots subjected to thinning and burning treatments. The organic matter in the whole soils and their humic and density-based fractions were characterized by elemental analysis and solid state 13C NMR spectroscopy. Our data revealed certain thermal induced composition changes in SOM fractions occurred during burning process depends. We attributed those structural differences observed in humic (HA) and fulvic (FA) acid fractions from burnt only and thin/burn treatment sites to complete combustion of ground vegetation in burn only sites relative to thin/burn sites containing partially burnt or non-charred plant debris. Those changes were involved mainly with alkyl C, O-alkyl C, and carbohydrate functional groups, implied that most prominent reactions occurred during this low-intensity burning process involved dehydrogenation, de-oxygenation, and decarboxylation. The limited structural changes of SOM fractions suggested the prescribed burning and thinning treatments had very low impact on changing composition of organic C forms in the soils studied, indicating that low intensity fire treatments in this ecosystem would not severely affect any structural changes in organic matter forms.