## 4 Discussion  
In this study, we sought to characterize the bioenoses on historical sandstone surfaces with different biodeterioration patterns (BPs) of the Northern Pergola in subsequent winter and summer seasons. Macroscopic analysis of the Pergola's slab surface revealed the presence of mosses (M), lichen crusts (LC), and green (GP) and yellow patinas (YP). The degradation potential of mosses is based primarily on the physical interaction with the stone surface, especially in places where stone slabs are joined. Additionally, mosses accumulate water, which helps to retain the humidity necessary for the growth of lichens and microorganisms. Lichens are symbiotic organisms composed of the cells typical for algae or cyanobacteria and fungi. All lichen communities show biodeteriorating  
Figure 10: Acidifying activity of the selected bacteria strains (1–32) isolated in summer (**a**) and winter (**b**) seasons from biofilm surfaces located on the Northern Pergola. Heat maps present the pH after 24, 48 and 72 h of different bacterial isolates incubation in [PERSON] liquid medium. The data represent averages of three independent experiments. abilities [38]. They cause mechanical damage due to the penetration of their thallus as the result of their expansion and contraction. They have the unique ability to produce chemical compounds that are characteristic to them. The number of identified substances produced by lichens as secondary metabolites is estimated at about 800. Some of them are strong chelating compounds, which have the ability to selectively remove certain metal ions, such as calcium or magnesium ions, from the rock/stones and these features are correlated to polar groups such as -OH and -COOH (e.g., lecanoric acid produced by _Lecanora_ sp.) [39; 40]. These substances play a significant role in the biodeterioration and bioweathering processes. Moreover, these compounds show antibacterial and antifungal activity, and an ability to absorb harmful UVA and UVB rays, and thus fulfill the role of a photoprotector [39; 41; 42]. All these features affect the formation of the entire biocenosis including microbiome. Unfortunately, most of the literature data concern calcium carbonate minerals, especially different types of limestones, which are more reactive to acid solutions than sandstone [43]. Most sandstone is composed of quartz or feldspar (both silicates) and is thus a mineral more resistant to weathering processes at the Earth's surface, but cementing materials may be either silicate minerals or non-silicate minerals, such as calcite [43]. Thus, mosses and lichens may be an important factor of sandstone bioweathering processes. Most of the data concerning the presence of mosses and lichens describe the biocenoses occurring on sandstone surfaces in tropical zones and in Great Britain [8; 9; 22; 38; 44; 45]. Therefore, the results of microbial diversity obtained for the Pergola surfaces were compared with results obtained for microbiota inhabiting sandstones in other climatic zones or other types of stones. For the Angkor temples complex in Cambodia in tropical monsoon climate, with distinctive rainy and dry seasons, visible biocenoses on monuments' sandstone surfaces consisted mainly of different filamentous and coccoid cyanobacteria, along with green algae, other bacteria, and, in some cases, fungi. Some biocenoses were dominated by the lichen community (_Leprarietum_, _Cryptothecietium_, _Pyxinetum_), and some moss species were identified [22; 38]. Generally, their composition is different from that observed on the Pergola surfaces. Mosses and lichens species dominating Pergola surfaces were also observed on other historical buildings located in Poland built of other materials than sandstone. The same species (excluding the _Homalothecium sericeum_) were also identified as predominant taxa on bricks and wooden historical buildings in the Former Auschwitz II-Birkenau State Museum. The barracks' exteriors were colonized by bryophytes, lichens, and, to a lesser extent, algae [46].