## 4 Discussion
Since the Pergola has not been cleaned in the last decade, it is legitimate to state that the biofilm under study is already stabilized and the pioneer organisms (algae, autotrophic bacteria, etc.) have been replaced by successors. The maturity and stability of the biofilm present on stone surfaces of the Pergola may be the reason for the relatively low abundance of Cyanobacteria phylum representatives in the studied biocenoses. Our results are contrary to the results obtained by [PERSON] et al. [47] for consortia responsible for the biodeterioration of Angkor temples in Cambodia. They collected two types of samples from two monuments made from sandstone: exfoliated/degraded sandstone materials loosely on sandstone block and visible biofilms on the sandstone wall. In sandstone exfoliation sediments they observed domination of heterotrophic bacteria (Actinobacteria, Proteobacteria and Acidobacteria), while Cyanobacteria and Chloroflexi were more abundant in biofilms samples. The differences in microbial composition described above may result from the highly different climate zones in Poland and Cambodia. Similar conclusions were derived on the basis of analyses made for tombstones located in different continents [48]. Structure of bacterial and eukaryotic communities presented on tombstones were significantly affected not only by climate, but also by rock type (limestone or granite). In the case of Pergola, the stone surface is eutrophicated and other microorganisms, such as microfungi, heterotrophic bacteria, and nitrophilous lichens (e.g., some species of _Caloplaca_or _Candelariella_) can develop. Therefore, in this situation, the chemical composition of the stone may become less important [8]. The alpha diversity analyses showed that observed bacterial communities on Pergola's surfaces are more diverse than the fungal ones. Similar results were obtained even for interior sandstone structures of the Rotunda of Sts. Felix and Adauctus, which is a part of the Wawel Royal Castle located in Krakow, Poland [49] or for limestone and granite tombstones [48]. [PERSON] et al. [47] observed that the alpha diversity of the bacterial community is also due to the depth from which the sample was taken for analysis (the lowest diversity was observed in the bottom depth layers of biofilms collected from Angkor temples). Noteworthy, richness of microbial communities on Pergola's surfaces as well as their structures are more similar in summer than in winter when the diversity across sampling sites is more versatile. The bacteria and fungi diversity in biocenoses on the historical Pergola at the phylum level (Supplementary Figure S3) showed similarities with the biodiversity observed in samples of biofilms on sandstone slabs in Belfast and Oxford [9; 45], and in the West Lake Cultural Landscape of Hangzhou in China [50]. Moreover, in the case of Pergola, taxonomic composition at the phylum level remained constant regardless of the season of the study. Differences were observed at lower taxonomic levels (families, genus). Independently from the seasons, biocenoses on the Northern Pergola were dominated by sequences representing the genera _Sphingomonas_ spp. Sphingomonadales were also most abundant in biofilms on sandstone in Oxford [9] and on stone surfaces of UNESCO's World Heritage listed monuments and exteriors of the temples located in the West Lake Cultural Landscape of Hangzhou in China [50]. They were also identified on carbonate stones of a medieval church in Italy [51], as well as on granite and limestone tombstones in different climatic zones [48]. On the surface of Pergola sandstone slabs, bacteria belonging to the phylum Acidobacteria and Actinobacteria were notably abundant as in Oxford [9], Hangzhou (China) [50], and in Angkor temples complex in Cambodia [47]. Moreover, in samples from Pergola's biocenoses, bacteria belonging to the phylum Firmicutes and Gemmatimonadetes were also identified. [PERSON] et al.