Comparison of elementary and humus composition of woody plants before and after burning

Abstract

Charred woody plant fragments are widely distributed in Japanese Ando soils (Kurobokudo) containing Type A humic acids with a high degree of darkening. In this study, to gain more information about the nature, properties, and role of charred woody plants produced during the burning of vegetation by man and wild fires, the elementary and humus composition of non-charred and charred (at 250°C for 30 min) woody plants was compared. The woody plant samples used consisted of powdery debris of twigs and branches from 10 evergreen broad leaf and 10 deciduous broad leaf trees, as well as 10 coniferous trees. In all the woody plants studied, the carbon and nitrogen contents increased considerably after burning, while the hydrogen and oxygen contents and the H / C, O/ C, and C / N ratios decreased remarkably. Furthermore, after burning, the extraction ratios of humic and fulvic acids decreased markedly, while the degree of darkening of the humic acids increased substantially. Although the absorption curves of the humic acids obtained before burning showed the presence of lignin- and tannin-like structures, their specific absorption bands mostly disappeared after burning. In the charred woody plants, Type B humic acids (medium degree of darkening) predominated with a small proportion of Type A humic acids. It was very difficult to differentiate the 3 types of woody plant species based on the changes in various parameters of elementary and humus composition associated with the burning of woody plants.