Organic boundaries between a moss species and a limestone as analyzed by multiple micro-spectroscopic methods

•This study characterized the boundary regions between a moss and a limestone.•Elemental distributions, polysaccharides and bacterial flora were analyzed.•Multiple micro-spectroscopic nondestructive methods are conducted.•Polysaccharides containing sulfur can fix the moss on the rock.•The polysaccharides retain nutrients including N on the limestone. In order to examine direct interactions of mosses and rocks before soil formation, boundary portions between a moss species (Homomallium japonica-adnatum) and a limestone have been measured by visible, Raman and infrared (IR) micro-spectroscopy, scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDS), Field Emission (FE) SEM with EDS and X-ray photoelectron spectroscopy. Bacterial flora was also analyzed. Although some enhancements of chemical weathering of the limestone could be recognised, physical weathering effects by the present moss species were not major. No significant differences in bacteria flora are detected between the limestone surfaces with and without mosses. On the other hand, at the boundary of the moss and the limestone, S-containing organic portions with N were detected. Their IR spectra indicated that these portions are mainly polysaccharides. One of them can be similar to a microbial polysaccharide biopolymer (gellan gum) produced by a bacterium Sphingomonas, which was detected in bacterial flora. Another was considered to be polysaccharides with sulfate-esters. Although their formation mechanisms need further study, these adherent polysaccharides can bind mosses to limestone, retaining nutrients and providing sites for further developments of plants.