Exploring causes of the decline of the lichenLecanora conizaeoidesin Britain: effects of experimental N and S applications

Abstract

The crustose lichen Lecanora conizaeoides has declined markedly around London with progressively diminishing sulphur dioxide pollution of the air since the 1960s. To identify the immediate causes of its decline, we applied S in the form of bisulphite (0·2 & 2 mM) and sulphate (2 mM), and N as nitrate (2 mM) to relict colonies of the lichen on beech trunks in a plantation in Windsor Forest. Growth of the lichen was monitored by estimating changes in percentage cover. By the end of a 25-month period of two-weekly treatments, all the chemical treatments had resulted in significant decreases in cover of L. conizaeoides compared to distilled water controls, with the 2 mM bisulphite causing the greatest loss. Bark surface pH was also lowered by the chemical treatments, but most by the 2 mM bisulphite applications. Similar results were obtained in two laboratory experiments where the nutrient applications were repeated under a controlled environment and thallus area monitored photographically. No evidence was obtained to support the hypothesis that growth of L. conizaeoides is stimulated by an elevated sulphur supply. We conclude that the disappearance of the lichen is linked to gradual increase in bark pH caused by the combined effects of a marked reduction in SO 2 emissions and rising emissions of NH 3 .

The lichens of Glasgow Botanic Gardens

“…It requires very acidic substrates, which were plentiful from the 19th to the late 20th centuries as a result of high levels of atmospheric sulphur dioxide caused by the burning of coal. Massara et al (2009) concluded that its retreat was linked to an increase in bark pH due to a combination of the reduction in sulphur dioxide emissions that followed the Clean Air Act of 1956 and rising emissions of ammonia originating from the catalytic convertors of road vehicles. Although once very common throughout the city, L. conizaeoides had not been recorded in Glasgow since 1991 (pers.…”

Monitoring Lichen as Indicators of Atmospheric Quality

“…Over time lichens could be affected under the SO 2 exposure and the morphological changes occur. Sulphur dioxide affects the growth of lichens: the smaller, more compacted thalli and decrease in cover were recorded (Massara et al 2009). Sulphur compounds caused reduction or absence of fruiting bodies.…”

Small increase in sub-stratum pH causes the dieback of one of Europe's most common lichens, Lecanora conizaeoides

“…Thus the reduced total S content of the spruce bark could exert an additional unfavourable effect on L. conizaeoides. Massara et al (2009) concluded from spraying experiments with different concentrations of bisulfite that the pH rather than the S supply controls the abundance of L. conizaeoides; however, as the pH was not manipulated independently of the bisulfite concentration, this conclusion is not completely convincing. The results of LaGreca and Stutzman (2006), who found L. conizaeoides on conifer bark of low pH in an area of eastern North America which was never exposed to SO 2 pollution comparable with that in Europe, are more supportive of the hypothesis that SO 2 and its derivatives formed in aqueous solution themselves are less significant for the vitality of L. conizaeoides than the pH itself.…”