title: On the dual nature of lichen-induced rock surface weathering in contrasting micro-environments.
abstract: Contradictory evidence from biogeomorphological studies has increased the debate on the extent of lichen contribution to differential rock surface weathering in both natural and cultural settings. This study, undertaken in Côa Valley Archaeological Park, aimed at evaluating the effect of rock surface orientation on the weathering ability of dominant lichens. Hyphal penetration and oxalate formation at the lichen-rock interface were evaluated as proxies of physical and chemical weathering, respectively. A new protocol of pixel-based supervised image classification for the analysis of periodic acid-Schiff stained cross-sections of colonized schist revealed that hyphal spread of individual species was not influenced by surface orientation. However, hyphal spread was significantly higher in species dominant on northwest facing surfaces. An apparently opposite effect was noticed in terms of calcium oxalate accumulation at the lichen-rock interface; it was detected by Raman spectroscopy and complementary X-ray microdiffraction on southeast facing surfaces only. These results suggest that lichen-induced physical weathering may be most severe on northwest facing surfaces by means of an indirect effect of surface orientation on species abundance, and thus dependent on the species, whereas lichen-induced chemical weathering is apparently higher on southeast facing surfaces and dependent on micro-environmental conditions, giving only weak support to the hypothesis that lichens are responsible for the currently observed pattern of rock-art distribution in Côa Valley. Assumptions about the drivers of open-air rock-art distribution patterns elsewhere should also consider the micro-environmental controls of lichen-induced weathering, to avoid biased measures of lichen contribution to rock-art deterioration.
authors.affiliation: CIBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, Campus Agrário de Vairão, 4485-661, Vairão, Portugal.|Departamento de Biologia, Faculdade de Ciências, Universidade do Porto, Edifício FC4, Rua do Campo Alegre s/n, 4169-007, Porto, Portugal.|Escola Universitaria de Enxeñeria Forestal, Universidade de Vigo, Campus Universitario A Xunqueira s/n, 36005, Pontevedra, Spain.
authors.forename: Joana
authors.initials: J
authors.lastname: Marques
authors.affiliation: CIBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, Campus Agrário de Vairão, 4485-661, Vairão, Portugal.|Departamento de Biologia, Faculdade de Ciências, Universidade do Porto, Edifício FC4, Rua do Campo Alegre s/n, 4169-007, Porto, Portugal.
authors.forename: João
authors.initials: J
authors.lastname: Gonçalves
authors.affiliation: CIBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, Campus Agrário de Vairão, 4485-661, Vairão, Portugal.|Departamento de Biologia, Faculdade de Ciências, Universidade do Porto, Edifício FC4, Rua do Campo Alegre s/n, 4169-007, Porto, Portugal.
authors.forename: Cláudia
authors.initials: C
authors.lastname: Oliveira
authors.affiliation: Dipartimento di Scienze della Vita e Biologia dei Sistemi, Università degli Studi di Torino, Viale Mattioli 25, 10125, Torino, Italy.
authors.forename: Sergio E
authors.initials: SE
authors.lastname: Favero-Longo
authors.affiliation: Escola Universitaria de Enxeñeria Forestal, Universidade de Vigo, Campus Universitario A Xunqueira s/n, 36005, Pontevedra, Spain.
authors.forename: Graciela
authors.initials: G
authors.lastname: Paz-Bermúdez
authors.affiliation: CIBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, Campus Agrário de Vairão, 4485-661, Vairão, Portugal.|Departamento de Biologia, Faculdade de Ciências, Universidade do Porto, Edifício FC4, Rua do Campo Alegre s/n, 4169-007, Porto, Portugal.
authors.forename: Rubim
authors.initials: R
authors.lastname: Almeida
authors.affiliation: Departamento de Edafología y Química Agrícola, Facultad de Farmacia, Universidad de Santiago de Compostela, 15782, Santiago de Compostela, Spain.
authors.forename: Beatriz
authors.initials: B
authors.lastname: Prieto
mesh_terms: D004777:Environment; D005844:Geology; D008011:Lichens; D014887:Weather
keywords: Raman spectroscopy; X-ray microdiffraction; biodeterioration; biogeochemistry; biomineralization; image analysis; schist