Once upon a Time, There Was a Piece of Wood: Present Knowledge and Future Perspectives in Fungal Deterioration of Wooden Cultural Heritage in Terrestrial Ecosystems and Diagnostic Tools

Abstract

Wooden Cultural Heritage (WCH) represents a significant portion of the world's historical and artistic heritage, consisting of immovable and movable artefacts. Despite the expertise developed since ancient times to enhance its durability, wooden artefacts are inevitably prone to degradation. Fungi play a pivotal role in the deterioration of WCH in terrestrial ecosystems, accelerating its decay and leading to alterations in color and strength. Reviewing the literature of the last 25 years, we aimed to provide a comprehensive overview of fungal diversity affecting WCH, the biochemical processes involved in wood decay, and the diagnostic tools available for fungal identification and damage evaluation. Climatic conditions influence the occurrence of fungal species in threatened WCH, characterized by a prevalence of wood-rot fungi (e.g., Serpula lacrymans, Coniophora puteana) in architectural heritage in temperate and continental climates and Ascomycota in indoor and harsh environments. More efforts are needed to address the knowledge fragmentation concerning biodiversity, the biology of the fungi involved, and succession in the degradative process, which is frequently centered solely on the main actors. Multidisciplinary collaboration among engineers, restorers, and life sciences scientists is vital for tackling the challenges posed by climate change with increased awareness. Traditional microbiology and culture collections are fundamental in laying solid foundations for a more comprehensive interpretation of big data.

Keywords: Aspergillus niger; Coniophora puteana; FTIR; Serpula lacrymans; architectural wood biodeterioration; cellulase activity; extremotolerant fungi; lignin degradation; metabolic plate assays; wood-decaying fungi.

Figure 3

Macroscopic wood appearance and drawings illustrating healthy and rotted wood patterns as can be observed under a microscope. (A,B) Healthy wood: (B) intact tracheid cell walls (drawn based on [45]). (C–E) BR decay: (C) wood cubical pattern; (D) The degradation of cellulose in woody cell walls leaves a residual network of lignin. Cell walls collapse and appear distorted (drawn based on [5]); (E) numerous splits in the secondary walls of tracheids (drawn based on [46]). (F–H) WR decay: (F) white stringy rot; (G) simultaneous white rot – in the dark areas lignin, cellulose and hemicellulose are degraded approximately at the same rate starting from the lumina (drawn based on [39]); (H) preferential white rot, lignin in secondary walls, and ML is selectively degraded while the rest of the cellulose rich cell wall is maintained and cells result separated from the adjacent (drawn based on [47]). (I–K) SR decay: (I) soft rotted wood; (J) SR type I, the fungal infection caused many cavities inside the wood cell wall especially in the S2 layer (drawn based on [45]); (K) SR type I, chains of diamond-shaped cavities extend longitudinally through the S2 cell wall layer (drawn based on [48]).

Figure 4

Examples of macroscopic wooden artefact alterations. (A) Temple woodblock affected by white rot; (B) 19th-century polychrome wood mask; (C) recto and verso of Poesia by Kokocinski, a composite artwork (paper and paint on multi-layered wooden panel) affected by fungal colonization. (D) Discolored painted layer of a votive statue representing the crucifixion; (E) biological attack on the wooden ceiling of the Palazzo Tarquini-Savelli, Marta (VT), Italy.

Figure 1

Immovable and movable terrestrial wooden cultural heritage examples. (A) Teatro Farnese, Parma, Italy (courtesy of Andrea Schiaretti); (B) gilded door, Granada, Spain; (C) ceiling of the Gyeongbokgung Palace, Seoul, South Korea; (D) Torre dell’Elefante, Cagliari, Italy; (E) wooden sarcophagus on display at the Egyptian Museum in Turin, Italy; (F) view from the Muwisa Temple, South Korea; (G) wooden roof of the San Lorenzo Cathedral in Viterbo, Italy; (H) wooden sculpture of Sant’Efisio in Cagliari, Italy; (I) the coach of Sant’Efisio in Cagliari, Italy (courtesy of Angelo Mocci); (J) wooden pillow of Queen Mureyong, Gongju National Museum, South Korea; (K) upper part of the wooden seat Magistratus Sessio in the council chamber of the Municipality of Viterbo, Italy; (L) Palazzo dei Priori, coffered ceiling with paintings and stuccos, Viterbo, Italy (courtesy of Emma Aronne).

Figure 2

Wood, from tree to chemical composition. (A) tree, (B) trunk section, (C) conventional cell-wall model characterized by five cell-wall layers. The layers are the middle lamella (ML), the primary wall (PW), and the three-layer secondary wall (SW): outer (S1), middle (S2) and inner secondary wall layer (S3). (D) cell wall chemical composition across its different layers. The image is original; (B,C) are drawn based on [16].

Figure 5

Geographical distribution of the wooden cultural heritage studied in the 81 papers for which mycological investigations were performed. The countries are indicated with the international three letters alpha-3 code: KOR: South Korea, RMN: Romania, ATA: Antarctica; ITA: Italy, EGY: Egypt, SVK: Slovakia, CUB: Cuba, POL: Poland, PRT: Portugal, ARG: Argentina, AUT: Austria, CHI: Chile, CHN: China, LVA: Latvia, RUS: Russia, SRB: Serbia, SJM: Svalbard, CAN: Canada, CHE: Switzerland, CZE: Czechia, DNK: Denmark (Greenland), FRA: France, GER: Germany, HRV: Croatia, IDN: Indonesia, JOR: Jordan, MAR: Morocco, MDA: Moldova, MKD: North Macedonia, PHL: Philippines.

Figure 6

Papers sorted by Köppen–Geiger climatic regions. AF: tropical rainforest climate; Bwh: hot desert climate; Cfa: humid subtropical climate; Cfb: temperate oceanic climate or subtropical highland climate; Csa: hot-summer Mediterranean climate; Dfb: warm-summer humid continental climate; Dfc: subarctic climate; Dwa: humid continental climate; EF: ice cap climate. The x-axis indicates the nr of papers.

Figure 7

High taxonomic rank distribution of the 1167 fungal records found on wooden cultural heritage artefacts. Division (central ring) and class (outer ring). Different shades of the same color indicate the classes belonging to the same division.

Figure 8

Prevalence of phyla sorted by climatic sub-areas. Values are presented as a percentage of the total taxa recorded (indicated above each column) for each climatic sub-area. Ascomycota is represented in blue, Basidiomycota in red, and Mucoromycota in grey. AF: tropical rainforest climate; Bwh: hot desert climate; Cfa: humid subtropical climate; Cfb: temperate oceanic climate or subtropical highland climate; Csa: hot-summer Mediterranean climate; Dfb: warm-summer humid continental climate; Dfc: subarctic climate; Dwa: humid continental climate; EF: ice cap climate.

Figure 9

Wooden cultural heritage genera frequency based on the 1167 fungal records. (A) Ascomycota, (B) Basidiomycota. To improve reading, the genera found have been ordered by frequency, while those found only once have been merged and indicated as “Occasional genera”. Values are expressed as percentages.

Figure 10

Venn diagram depicting fungal species sorted by the main climatic groups.

Figure 11

Positive responses to screening plate assays. (A) Laccase test (PDA guaiacol) of Trametes versicolor from Antarctic plant [202]; (B) cellulase activity (CMC agar flooded with Lugol solution) of Pseudogymnoascus pannorum CCFEE 5287; (C) cellulase activity (PDA_CMC flooded with Congo Red) of Penicillium oxalicum; (D) lignin peroxidase activity (Cz_Azure B) recorded for strain CCFFEE 10077; (E) xylanase activity (PDA_xylan) of Penicillium oxalicum; (F) ligninase activity (PDA lignin supplementedremazol) of Eupenicillium rubidurum; (G) Mn peroxydase activity (Cz_Phenol Red) of Aspergillus niger vs. negative control plate.