Biological colonization patterns on the ruins of Angkor temples (Cambodia) in the biodeterioration vs bioprotection debate

The biological colonization present on the temples of the UNESCO World Heritage site of Angkor is wide and relevant, but a debate on its biodeteriorative and bioprotective effects is now developing. We investigated the biological patterns observed on two temples (Ta Nei and Ta Keo) exposed to different microclimatic conditions, in order to assess the damage caused by the communities present on the stone. We analyzed the penetration (depth and spread) into the stone, and the degree of decohesion of seven communities (green algae, cyanobacteria, lichens and mosses). The microscopic analyses highlighted a clear interaction between organism and stone, displaying a trend of increasing harmfulness from the community of the green algae (Trentepohlia) up to the moss communities. All the lichen communities show biodeterioration abilities: the Pyxine community seems more aggressive than the Lepraria and Cryptothecia communities, and more also than the cyanobacterial communities. The positive effects of the lichen cover in reducing dangerous evaporation processes cannot outweigh the negative effects of their hyphal penetration. Light forest cover seems beneficial for the conservation of the Angkor monuments since it reduces evaporation processes, but further studies should be carried out so as to find an optimal balance between contrasting factors.