Urban environmental influences on heterocyst investment in Leptogium cyanescens (Collemataceae)

Abstract

Cyanobacteria perform biological nitrogen fixation (BNF) in specialized cells called heterocysts, and their differentiation is closely associated with the balance between carbon and nitrogen quantities. Although BNF is an important ecosystem function, there are no studies verifying the production of heterocysts in cyanolichens from different habitats. Therefore, we compared the densities of heterocysts in specimens located in an urban and a forested area. Leptogium cyanescens (Collemataceae) specimens were collected at the Universidade Federal de Lavras (urban area) and at Unilavras – Reserva Biológica Boqueirão (forested area). We detected and analyzed 10,758 heterocysts in specimens from the urban area and 7,217 heterocysts in specimens from the forested area. Specimens from the urban area had higher heterocyst densities per total cell count than specimens from the forested area, producing on average 384 heterocysts per total cell count in the urban area and 257 heterocysts per total cell count in the forested area. These differences may be a consequence of an imbalance between carbon and nitrogen quantities in the sampled urban and forested areas. Increased availability of carbon dioxide may induce demand for nitrogen, thus increasing heterocyst differentiation to obtain more nitrogen.