Capacity of biological soil crusts colonized by the lichen Diploschistes to metabolize simple phenols

Abstract

Aims In biological soil crusts (biocrusts) in which Diploschistes diacapsis (Ach.) Lumbsch is the predominant lichen (DIPLOS biocrusts), metabolic activity increases in response to wetting, and hot water-soluble components that react to Folin-Ciocalteu reagent are consumed during the mineralization process. We aimed to determine the types of compounds that contribute to the high rates of respiration. Methods Aliquots of aqueous extracts (80°C, 24 h) obtained from DIPLOS biocrusts incubated for 10 days in the dark, at 25°C and at different levels of moisture (M1, 9.6 %; M2, 26 %; M3, 52 % and M4, 78 %, expressed as the percentage of water retained at field capacity), were analyzed by HPLC and LC/ESI/MS/MS. Results The intensity of the peaks in HPLC chromatograms decreased as the moisture level increased, and LC/ESI/MS/MS analysis revealed that the compounds are mainly diphenols (or very small polymers of these) and products derived from these via the metapathway of phenol metabolism. A mycosporine-like product, which is stable at low moisture levels, but metabolized at high moisture levels, was also detected. Conclusions DIPLOS biocrusts display high oxidative enzymatic activity that is capable of degrading phenols and that is probably associated with non-lichenized free living fungi proliferating at high moisture levels. The high rates of respiration associated with high humidity, together with the metabolism of compounds like mycosporines (with key functions in providing protection against UV radiation), may lead to structural collapse of the biocrusts under such conditions.