Fasi Wu

The surface of the Great Wall harbors a large number of non-vascular plants dominated by cyanobacteria, lichens and mosses as well as microorganisms, and form biocrusts by cementing with the soils and greatly alters the pore structure of the soil and the ecohydrological processes associated with the soil pore space, and thus influences the soil resistance to erosion. However, the microscopic role of the biocrusts in influencing the pore structure of the surface of the Great Wall is not clear. This study chose the Warring States Qin Great Wall in Weiyuan, Gansu Province, China, as research site to quantify thepore structure characteristics of the three-dimensional of bare soil, cyanobacterial-lichen crusts, and moss crusts at the depth of 0–50 mm, by using optical microscopy, scanning electron microscopy, and X-ray computed tomography and image analysis, and the precipitation infiltration process. The results showed that the moss crust layer was dominated by large pores with long extension and good connectivity, which provided preferential seepage channels for precipitation infiltration, while the connectivity between the cyanobacterial-lichen crust voids was poor; The porosity of the cyanobacterial-lichen crust and the moss crust was 500% and 903.27% higher than that of the bare soil, respectively. The porosity of the subsurface layer of cyanobacterial-lichen crust and moss crust was significantly lower than that of the biocrusts layer by 92.54% and 97.96%, respectively, and the porosity of the moss crust was significantly higher than that of the cyanobacterial-lichen crust in the same layer; Cyanobacterial-lichen crusts increased the degree of anisotropy, mean tortuosity, moss crust reduced the degree of anisotropy, mean tortuosity. Biocrusts increased the fractal dimension and Euler number of pores. Compared with bare soil, moss crust and cyanobacterial-lichen crust increased the isolated porosity by 2555% and 4085%, respectively; Biocrusts increased the complexity of the pore network models; The initial infiltration rate, stable infiltration rate, average infiltration rate, and the total amount of infiltration of moss crusted soil was 2.26 and 3.12 times, 1.07 and 1.63 times, respectively, higher than that of the cyanobacterial-lichen crusts and the bare soil, by 1.53 and 2.33 times, and 1.13 and 2.08 times, respectively; CT porosity and clay content are significantly positively correlated with initial soil infiltration rate (|r| ≥ 0.85), while soil type and organic matter content are negatively correlated with initial soil infiltration rate. The soil type and bulk density are directly positively and negatively correlated with CT porosity, respectively (|r| ≥ 0.52). There is a significant negative correlation between soil clay content and porosity (|r| = 0.15, p < 0.001). Biocrusts alter the erosion resistance of rammed earth walls by affecting the soil microstructure of the earth’s great wall, altering precipitation infiltration, and promoting vascular plant colonisation, which in turn alters the erosion resistance of the wall. The research results have important reference for the development of disposal plans for biocrusts on the surface of archaeological sites.

The Hexi Corridor is an arid region in northwestern China, where hypoliths are widely distributed, resulting from large amounts of translucent stone pavements. In this region, the water and heat distributions are uneven, with a descent gradient from east to west, which can affect the area’s biological composition. The impact of environmental heterogeneity on the distribution of hypolithic microbial communities in this area is poorly understood, and this is an ideal location to investigate the factors that may influence the composition and structure of hypolithic microbial communities. An investigation of different sites with differences in precipitation between east and west revealed that the colonization rate decreased from 91.8% to 17.5% in the hypolithic community. Environmental heterogeneity influenced both the structure and function of the hypolithic community, especially total nitrogen (TN) and soil organic carbon (SOC). However, the effect on taxonomic composition was greater than that on ecological function. The dominant bacterial phyla in all sample sites were Cyanobacteria, Actinobacteria, Proteobacteria, and Deinococcus-Thermus, but the abundances varied significantly between the sampling sites. The eastern site had the highest relative abundance of Proteobacteria (18.43%) and Bacteroidetes (6.32%), while the western site had a higher relative abundance in the phyla Cyanobacteria (62%) and Firmicutes (1.45%); the middle site had a higher relative abundance of Chloroflexi (8.02%) and Gemmatimonadetes (1.87%). The dominant phylum in the fungal community is Ascomycota. Pearson correlation analysis showed that the soil’s physicochemical properties were also associated with changes in community diversity at the sample sites. These results have important implications for better understanding the community assembly and ecological adaptations of hypolithic microorganisms.

Understanding how microbial communities adapt to environmental stresses is critical for interpreting ecological patterns and microbial diversity. In the case of the Gobi Desert, little is known on the environmental factors that explain hypolithic colonization under quartz stones. By analyzing nine hypolithic communities across an arid gradient and the effects of the season of the year in the Hexi Corridor of this desert, we found a significant decrease in hypolithic colonization rates (from 47.24 to 15.73%) with the increasing drought gradient and found two distinct communities in Hot and Cold samples, which survived or proliferated after a hot or a cold period. While Cold communities showed a greater species diversity and a predominance of Cyanobacteria, Hot communities showed a predominance of members of the Proteobacteria and the Firmicutes. In comparison, Cold communities also possessed stronger functions in the photosynthesis and carbon metabolism. Based on the findings of this study, we proposed that the hypolithic communities of the Hexi Corridor of the Gobi Desert might follow a seasonal developmental cycle in which temperature play an important role. Thus after a critical thermal threshold is crossed, heterotrophic microorganisms predominate in the hot period, while Cyanobacteria predominate in the cold period.

Mogao Grottoes, a UNESCO World Cultural Heritage Site since 1987, suffer from microbial colonization and deterioration of the wall paintings with visible appearance of black spots and fungal colonization in selective caves. In this study, Next-Generation Sequencing (NGS) and microscopical analyses were combined and used to reveal the microbial community compositions on wall paintings of the Mogao Grottoes. In addition, radioactive 14 C dating was applied to determine the possible infestation time of the fungal outbreak in history based on Bayesian chronological modeling. Results of SEM, fluorescence microscopy and polarizing microscopy showed collectively that the existing microbial hyphae were not viable. The dominant bacteria included Rhodococcus and Ralstonia mainly with unclassified_c_Eurotiomycetes while Aspergillus species were the predominant mycoflora in samples of the black spots and microbial biomass. Using 14 C dating results and historical documents together, the original mural was most likely painted in the Five Dynasties and Ten Kingdoms (939-942 ca. AD) while the repainting time and the mural were mostly probable in Song Dynasty (1002-1014 ca. AD), and the fungal remains were most likely formed in this historical period. With monitoring locations closer to the cliff, the higher bacterial diversity and lower fungal diversity detected were correlated with the higher relative humidity. Since the temperature and relative humidity were generally low in this area, unsuitable for microbial growth presently or in the normal time of the past, either earthen plaster preparation prior to the first painting or heavy rainfall events and leaky roof was most likely the initiator to the outbreak of the indigenous microbes to proliferate on the wall paintings. This study provided useful evidences on the microbial community and the time of a microbial outbreak event on ancient wall paintings in such an extremely arid climate condition.

Fungi and algae are specific microbial groups associated with the deterioration and safety of stone monuments. In this study, the high-throughput sequencing analysis was used to investigate the diversity, distributions, ecological functions, and interaction patterns of both fungal and algal communities on sandstone in the Beishiku Temple, located on the ancient Silk Road. Results showed that the core phyla of fungi were affiliated to unclassified Lecanoromycetes, Engyodontium , Knufia , Epicoccum , Endocarpon , and Cladosporium of Ascomycota whereas the phyla of algae were dominated by Cyanobacteria and Chlorophyta. Environmental factors of temperature, relative humidity, and light intensity were monitored simultaneously. The structure of microbial communities was much more strongly shaped by soluble ions of Cl - , Na + , NO 3 - than light intensity, moisture content or temperature, especially for weathered sandstone outside the caves. Co-occurrence network analysis suggested a more stable community structure was evident outside the caves than inside. The stronger positive connections and co-existence patterns detected indicate a strong adaptability of fungi and algae to the distinct oligotrophic microhabitats on sandstone. The metacommunity co-occurrence network exhibited the ecological predominance of fungi and most of the functional fungi in the biofilms outside the caves belonged to Lichenized group based on the FUNGuild prediction. These findings highlight the ecology and functions of stone-inhabiting microorganisms to further advance the current understanding and knowledge of sandstone biodeterioration for protection and management.