Conversion from Native Forest to Managed Ecosystems Alters Thermal Stability of Organic Matter in Soil Fractions in the Karst Region of Southwest China

Dr Zhangliu Du1, Ms Weiwei Zhu1

1Institute of Environment and Sustainable Development in Agriculture, Chinese Academy Of Agricultural Sciences, Beijing, China

Understanding the stability of soil organic matter (SOM) after land-use changes is of critical importance to C sequestration. The present study was to evaluate the thermal stability of SOM in different soil fractions after converting from the native forest (NF) to eucalyptus forest (EF), unused grassland (UG) and corn field (CF) in the Karst region of southwest China using thermogravimetry (TG) and differential scanning calorimetry (DSC) techniques. Soil samples were collected from the 0- to 10-cm layer and physically separated into four classes (i.e., >53, 53-20, 20-2 and <2 μm). The results showed that the derivatives of thermogravimetry curves (DTG) and DSC curves had two peaks, near 300 and 500°C for both bulk soil and fractions. The percentage of thermal labile SOM (weight loss in 200–400°C accounting for that in 200–550°C, %Exo1) and energy densities (ED) of SOM (energy release per unit SOM) declined with decreasing particle sizes. The TG-T50 (the temperature leading to half of total SOM loss) increased with decreasing particle sizes, and the DSC-T50 (the temperature at which half of energy released resulting from SOM combustion) was insensitive to the land-use type. Conversion from NF to UG and CF reduced the quantity but increased thermal stability of SOM in bulk soil, indicating by less weight loss at combustion, lower %Exo1 ratio, lower ED and higher TG-T50. Compared with NF, EF and CF significantly decreased thermal stability of SOM within the 53-20 μm and <2 μm fractions, reflecting by the higher weight loss, %Exo1 ratio and ED and lower TG-T50. We concluded that the human-disturbed altered thermal stability of SOM in bulk soil and fractions. Our findings highlight the importance of land-use managements on SOM stability and thus terrestrial C cycle.

Biography: My research interests lie in the field of terrestrial soil organic matter (SOM) biogeochemistry. I am interested in the mechanisms and process that act to stabilize and destabilize SOM in surface soils. Currently, I focus on the  feedbacks between the management options  (e.g., tillage, residues, manure, and biochar) and SOM transformations.

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