# Biological Risk for Hypogea: Shared Data from
## 4 Discussion
### Environmental and biotic Influences  
In both countries, microorganisms that had entered the ancient tombs and microorganisms that originally inhabited the tombs were able to grow in particular environmental conditions. The microbial composition varies in relation to environmental changes, which in turn increase the risk of a biological attack as observed from the very first studies conducted [28]. The microbial colonisation of the hypopeal surfaces is the result of selective, competitive and inhibitory dynamics among different microorganisms from rocks and from the air under diverse and changing environmental conditions. It is also the result of human activity and intervention which form part of the \"history of the site\". Furthermore, every process of colonisation is different from another, since each community is conditioned by the pioneer species which will in turn influence further processes [12]. The study conducted at Mogao Grottoes also showed some interesting results in that the diversity index of the fungal community was positively correlated with the building period of the caves, which had a greater impact than temperature and relative humidity of the caves [105]. Without disregarding the role of environmental factors, it seems possible that the opening time of the tombs to outdoor exchanges and human presence has a significant influence on its biodiversity. In fact, several studies which show the great impact that environmental and edaphic factors have in facilitating different taxa are discussed and summarised in Figure 5.  
Water originating from percolation, infiltration and capillarity, and at times from human presence along with flooding was found to be the most important factor. The level of humidity greatly affects the various microbial communities as in any archaeological context [30; 114]. Such an influence was also recently confirmed by studies conducted in Chinese tombs (Emperor [PERSON], 1600 years old), where humidity showed the highest degree of microbiological variance (19.2%) than all other environmental factors, followed by illumination (18.3%) and height (12.8%) [106]. In general, fungi were found to be more resistant to dryness, with respect to bacteria. Figure 5: Microorganisms occurring in hypopeal tombs and factors influencing their qualitative and quantitative composition (**a**); main factors affecting the microclimate stability, this last is the main goal to be achieved (**b**). (Original elaboration by the authors). Lighting conditions were also found to be a very important factor, especially for the Korean sites because, in such humid conditions, the development of phototrophic organisms arises if the amount of radiation exceeds <2 umoll photons m\({}^{-2}\) s\({}^{-1}\), which is approximately three orders of magnitude less than full sunlight [1]. In the areas adjacent to the opening or near artificial sources of light, photoautotrophs grow as they are also aided by the high concentration of CO\({}_{2}\) (sometimes ten times higher than those in the atmosphere) [8]. Data from other hypogea, such as catacombs, show that the spectral composition of the light selects different taxonomic groups. Due to their different photosynthetic pattern, green algae and diatoms are favoured by emissions peaking in the blue and red parts of the spectrum, while cyanobacteria are favoured by the emissions in the green and orange-red ones [115]. Furthermore, temperature also greatly influenced the biological risk and for this reason, a risk assessment of microbial colonisation in the Korean sites suggested establishing three ranges of temperature and the risk conditions that occur when temperatures are above 22 \({}^{\circ}\)C [6]. In the Italian sites, we observed a higher risk at the end of summer, when the thermal heating reaches below ground, but no precise evaluations have been made. Inside a hypogean, the various walls can be at different risks of biological colonisation. When analysing Korean Tomb No.