This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The biopolymer lignin—one of the most important carbon reservoirs in plants and soils—not only decays through fungi or bacteria but can also be chemically attacked by iron linked to reactive oxygen species, without the involvement of microorganisms. When this happens, lignin is converted into methanol and subsequently into formaldehyde.
That is shown by a study conducted at Heidelberg University's Institute of Earth Sciences. The researchers also proved that this conversion takes place in natural soils—solely through wetting and without adding chemicals. This form of lignin degradation shines a light on a previously overlooked abiotic process that is related to Earth's carbon cycle and can have implications for trace gas fluxes and atmospheric chemistry.
The paper is published in the journal Nature Communications. Lignin constitutes a considerable part of terrestrial nonfossil organic carbon and gives wood and other plant matter their solidity. Characteristic of the biopolymer are so-called methoxy groups (–OCH₃).
The compounds methanol and formaldehyde are best known as important industrial chemicals, but they also develop naturally and, in the soil, serve as carbon and energy sources for microorganisms. It was previously unknown that an iron-induced process of lignin decay can be an important source of both compounds. Iron minerals are natural components of many soils, and reactive oxygen species—oxygen-containing molecules with very high chemical reactivity—can also form there, particularly under changing environmental conditions.
When reactive iron-oxygen species attack lignin without the involvement of microorganisms, the methoxy groups (–OCH₃) are directly released from the biopolymer. Previously known decay pathways only liberate the methyl share of such groups. In the course of demethoxylation, methanol and subsequently formaldehyde are formed under natural conditions.
"The reaction takes place at ambient temperature and under normal pressure in water, and will only intensify at higher temperatures. So far it has only been known from industry—using temperatures of over 285 degrees Celsius, at higher pressure and in a hydrogen atmosphere," explains Dr. Jonas Hädeler from the Institute of Earth Sciences, who carried out the laboratory experiments in the biogeochemistry research group led by Dr.
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