Air pollution affects lichen species richness, species density, relative growth form abundance and their secondary metabolite production: a case study in Kandy district, Sri Lanka

Abstract

Lichens are symbiotic associations between fungi and algae and/or cyanobacteria, consisting of three forms, viz: fruticose, foliose and crustose. Air pollution affects lichen diversity, percent cover, and density. The current study mainly compared the lichen species richness, density and relative abundance of each growth form among three selected sites with different degrees of pollution, viz: a site located in the Kandy City (S1), a site located 11 km away from the city (S2) and a site within a forest patch located ~12 km away from the Kandy city (S3). A random sampling method was used to collect lichens within a two km distance in the three selected sites. Percent cover and density were determined using a quadrat ladder. Acetone extracts of lichens were subjected to thin-layer chromatography (TLC), and secondary metabolites were identified by visualizing under UV (254 and 365 nm) and by Rf values. A total of 24 lichen species were collected (S1=8, S2=12, and S3=4). Percentage richness of crustose and foliose lichens was higher in S2 compared to S1, while Leparia sp. and Lecanora sp. were common in S1 and S2. Atranorin, salazinic acid, and zeorin were detected as common compounds from lichens in S1 and S2 sites, exhibiting photoprotecting and antioxidant properties. Fumarprotocetraric acid, which tolerates harsh environmental conditions, and Physodalic acid, which is produced in response to pollution stress were detected from lichens from S1. Norstictic acid was identified in lichens from S2. The results show a difference between the lichen community and secondary metabolites among the three sites.

Keywords

• air pollution
• lichen density
• lichen species richness
• secondary metabolites
• tlc analysis