Lignin phenols derivatives in lichens.

Area of Science:

• Biogeochemistry
• Organic Chemistry
• Ecology

Background:

• Lignin, a complex polymer in plant cell walls, provides structural support and defense.
• Understanding lignin composition across different plant taxa is crucial for tracing carbon cycling and ecosystem functions.
• Previous studies have characterized lignin in higher plants, mosses, and algae, but lichens remain understudied.

Purpose of the Study:

• To analyze the lignin monophenol composition in various lichen species using cupric oxide oxidation.
• To compare the syringyl (S), vanillyl (V), and p-hydroxyl (P) phenol ratios in lichens with those in other plant groups.
• To investigate the potential contribution of non-lignin phenols to the oxidation products and assess lichens as a source of soil and hydrosphere aromatics.

Main Methods:

• Cupric oxide (CuO) oxidation of dried lichen samples from diverse systematic groups.
• Gas chromatography-mass spectrometry (GC-MS) analysis to identify and quantify lignin-derived phenols (S, V, P units).
• Calculation of molecular ratios (S/V, S/P) and acid/aldehyde ratios to characterize lignin structure and potential non-lignin contributions.

Main Results:

• Syringyl structures were found to strongly dominate over vanillyl and p-hydroxyl structures in most lichens (S/V ratios: 7-583; S/P ratios: 3-30).
• This syringyl dominance distinguishes lichens from algae and mosses (where p-hydroxyl phenols dominate) and higher plants (with lower S/V ratios).
• Phenol and acid/aldehyde molecular ratios in lichens differed from higher plant lignin, suggesting the presence of non-lignin phenols in CuO oxidation products.

Conclusions:

• Lichens possess a unique lignin signature characterized by a high abundance of syringyl units, differing significantly from other plant lineages.
• The composition of CuO oxidation products indicates that lichens may contribute non-lignin aromatic compounds to environmental samples.
• Lichens can be a substantial source of aromatic structures in soils and the hydrosphere, particularly in regions with abundant lichen populations.