Effects of fire on soil organic matter in northern Amazonian forest fragments

Abstract

Forest fires incorporate pyrogenic organic matter into the soil, affecting the characteristics of soil organic matter (SOM) due to its high aromaticity, increasing its renewal time. However, the factors that control the concentration of pyrogenic organic matter and its chemical composition and structure are still little known. Forest fragments dispersed in a savanna matrix of the northern Brazilian Amazon are frequently impacted by fires, which can affect the composition of SOM within the fragments. The aim of this study was to analyse the chemical composition of SOM in the border and interior of six forest fragments in the Roraima savanna, in the northern Brazilian Amazon. Soil samples were collected at 10-cm intervals up to 1 m in depth at the border and in the interior of each fragment. Soil organic material concentration was determined with 10% HF solution and its elemental composition, thermogravimetric index, and 13C CPMAS NMR spectroscopic analysis were determined. There was no significant difference in the aromaticity index between border and interior. The concentration of alkyl C structures between border (22 to 25%) and interior (19 to 29%) indicated the occurrence of medium-intensity fires in the study area. The thermogravimetric analysis showed no significant difference in the thermal stability of SOM between border and interior. Our results showed no pronounced difference in SOM quality up to 1 m depth between the border and the interior of the evaluated forest fragments, indicating that this compartment is stable throughout the fragments.

Temporal changes in soil chemical compositions in acidified mountain forest soils of Czech Republic

“…The aromaticity index decreased dramatically with increasing soil profile depths (F > H > A > B), which means the aromatic content increased with depths. A similar result was found by Zech et al (1989) and Silva et al (2022), showing that the content of aromaticity increased from L to B horizons. It was contrast to the finding of Ohno et al (2014) where the abundance of condensed aromaticity of SOM was much lower in subsoil under coniferous and deciduous forests due to the adsorption of aromatic compounds to the minerals present in the soil profiles.…”

“…Furthermore, aromatic compounds were more likely adsorbed onto the soil particles than mobile in the soil solution through the soil profile (Thai et al 2022;Ohno et al 2017). Besides that, the high inputs of root lignin and cool climate in the study sites were considered as a cause of stability in the aromaticity content in the soil under spruce and in the subsoil horizons (Zech et al 1989;Silva et al 2022).…”