Transcript Lecture 11
BIOLOGY 3404F EVOLUTION OF PLANTS Fall 2008 Lecture 11 Tuesday October 28 LICHENS, BRYOPHYTES AND AIR POLLUTION Background and Cause(s) Paris (Nylander, 1866); Manchester (Grindon, 1859) Lichen Desert: an area with no foliose or fruticose lichens • CAUSE(s): 1. SO2 (and H2SO4, etc.) deposition – algal layer fades within a few months of exposure (chlorophyll is converted to phaeophytin through loss of Mg) and lichen dies. Lichens and bryophytes are susceptible only at high humidities 2. There is some argument over the roles of toxicity or desiccation as cause of urban lichen deserts (some evidence for drought – lack of dew; elevated temperatures – heat island effect; and rapid wetting and drying cycles in urban environments). Background, II • Bioaccumulation of heavy metals and radionuclides by lichens makes them great monitors of even low-level pollution (see below) • Acid Rain: Are lichens sensitive to acid rain? An area of interest of Dianne Fahselt at UWO. Yes, sometimes: May cause thallus bleaching and reduced photosynthesis, necrosis, or reduced N-fixation in species with cyanobacterial photobionts. MAPPING Mapping II 1. A 1971 study in Britain with 15,000 school children mapping easily identified lichens gave a very clear map of heavily polluted areas in Britain 2. Hawksworth & Rose, 1970 Nature 227:145-8. Came up with a qualitative scale, and delimited 10 zones ranging from 0 (epiphytes absent), 1 (Pleurococcus viridis present on tree bases only; SO2 >170 ppm); to 10 (pristine). Usnea and Lobaria appear in Zone 9 (< 30 ppm SO2) 3. Huge field with many research contributions, listed in The Lichenologist Mapping III 4. Index of Atmospheric Purity (Leblanc & Sloover, 1970, Can J Bot 48: 1485-96 + maps) based on epiphytic lichens and bryophytes found on trunks of deciduous trees IAP = ∑ (Qi X fi) ÷ 10 For n species, where • Qi is “ecological index” for species i (= # neighbour lichen/bryophyte species) • fi is coverage value (i.e., area covered on a tree trunk; 1-5) for species i Mapping IV Leblanc & Sloover, 1970 • This study was of the greater Montreal area: lots of trees within the city, serious atmospheric pollution (map). • Zone I (highest pollution, IAP 1-5.5) had only 12 species, all at low frequency (2-8% of sites) except the alga Protococcus viridis, present in 100% of Zone I sites • 74 species were recorded in Zone V (IAP > 75.5), the cleanest air environments • The most pollution-tolerant lichen was Parmelia sulcata; in Europe, a similar study listed Hypogymnia physodes as most pollution tolerant (absent from the Montreal list since they surveyed trunks of predominantly deciduous trees) • The top of Mont Royal reached Zones III and IV. Radiation • Lapps (= Sami) have a 10,000 year history of reindeer herding across northern Scandianavia • Natural winter food of reindeer is dominated by species of Cladina (“reindeer lichen”), which like most fungi and lichens is a good bioaccumulator of radioactive substances • The Swedish limit for food (including reindeer meat or milk) is 300 becquerel Strontium90/kg Radiation • Following the 1986 Chernobyl nuclear reactor disaster, some reindeer were at 2,000-30,000 Bq/kg; however, of 21,00 reindeer slaughtered (and buried), 5,000 were below Bq 300 • Solutions include feeding reindeer hay in feedlots, or wait – in 36 years, a reindeer with 8000 Bq will drop to 1000 • but will it be alive? • will replacement animals be just as contaminated? Mushrooms as bioaccumulators • Mushrooms are also great bioaccumulators, including radioactive cesium (137Cs) • Following Chernobyl, mushrooms across northern Europe and the Ukraine had levels of 137Cs reaching 15 Bq (400 pCi)/g dry weight, while lichens were in the range of 0.06-1.3 Bq/gdw (Umbilicaria and Hypogymnia were among the high rad group); litter, peat and soil sampled were 0.02-0.37 Bq/gdw • Radioactive potassium (40K) was also high in fungi, and the hypothesis was made that Cs is absorbed to fulfil the K requirements of the fungus (and, since it is NOT K, they keep taking up more) Bryophytes and Pollution • POLLUTION-TOLERANT MOSSES: Ceratodon purpureus, Bryum argenteum, Sphagnum recurvatum (these tend to have fast growth rates and short-lived protonema, which are more sensitive than gametophytes). • “COPPER MOSSES” (e.g. Melichoferia) thrive in high-copper areas (may survive 160 ppm Cu vs. max 35 ppm in other mosses) • POLLUTION-SENSITIVE MOSSES: Grimmia pulvinata, Hypnum cupressiforme Pollution Monitoring • Pollution monitoring plants should: 1. Readily accumulate airborne pollution 2. Accumulation should vary inversely with distance from known source • • Natural content of pollutant (background) should be relatively constant Moss-bags can be used where suitable species are not present (e.g., Pleurozium schreberi, Sphagnum)