Ultrastructural Changes and Electrolyte Leakage from Ozone Fumigated Epiphytic Lichens

The ultrastructure of lichens and leakage of electrolytes fromthem were studied to assess the effects of ozone on four epiphytes.Bryoriacapillaris(Ach.) Brodo & Hawksw.,Bryoria fuscescens(Gyelnik)Brodo & Hawksw.,Hypogymnia physodes(L.) Nyl. andUsnea hirta(L.)Wigg. were fumigated with control (<10), 40, 150 and 300ppb ozone in controlled growth chambers for 2 and 4 week periods.The ultrastructural results suggest a direct effect of O₃oncarbon assimilation and storage in these lichens. Both the highconcentrations of ozone (150 ppb and 300 ppb) and longer exposuretime significantly increased starch volume and electron opacityof the pyrenoid matrix in chloroplasts ofU. hirtaandB. capillaris.Furthermore, inU. hirta, cytoplasmic lipid droplets and thenumber of pyrenoglobuli in pyrenoids were significantly increasedat higher ozone concentrations.B. fuscescensshowed little responseto ozone at the ultrastructural level. In bothBryoriaspeciesthe potassium leakage, and inB. fuscescensthe conductivity ofleachate, decreased during 4 weeks fumigation with high concentrations(150 and 300 ppb) of ozone. In most lichens, the total concentrationof K⁺was either unchanged or increased at 150 ppb O₃, suggestingthat no leaching due to membrane damage occurred, but K⁺uptakeby the lichens tended to increase at the concentrations of O₃used.Copyright1997 Annals of Botany Company Epiphytic lichens; Bryoria capillaris; Bryoria fuscescens; Hypogymnia physodes; Usnea hirta; electrolyte leakage; conductivity; potassium; ozone; ultrastructure     

Responses of Leaf Processes in a Sensitive Birch (Betula pendulaRoth) Clone to Ozone Combined with Drought

Saplings of an ozone sensitive clone of birch (Betula pendulaRoth,KL-5-M) were well-watered or exposed to mild drought-stresscombined with ambient or elevated (1.5xthe ambient) ozone for11 weeks in open-field conditions in central Finland. Stomatalresponse, visible injury, chlorophyll and nutrient content,and changes in cellular anatomy and plant growth were studied.Drought stress alone, in ambient ozone, reduced stomatal densityand stomatal conductance. Drought stress and ozone effects wereadditive, reducing total leaf number, foliage area and starchformation in mesophyll cells. Drought stress and ozone effectswere additive, increasing the N concentration in the leaves,the thickness of the upper epidermal cell wall, the number ofpectinaceous projections of mesophyll cell walls, and the vacuolartannin-like depositions and phenolic droplets, regarded as signsof activated stress defence mechanisms. The increase in specificfoliage mass, cytoplasmic lipids (younger leaves), and a condensedappearance of the upper epidermal mucilaginous layer were causedby both drought and ozone, but were not additive. The resultsshow that combined drought stress contributed to birch responsesto 1.5xcurrent ambient ozone concentrations, corresponding tocritical-level ozone exposure. The only beneficial effect ofdrought stress was the slight reduction of visible leaf symptomsinduced by ozone in autumnal leaves.Copyright 1998 Annals ofBotany Company Birch,Betula pendula, sensitive clone, ozone, drought, microscopy.