Nephroma Arcticum Research Articles

Volatile organic compound emissions from subarctic mosses and lichens

Plant volatile organic compound (VOC) emissions can drive important climate feedbacks. Although mosses and lichens are important components of plant communities, their VOC emissions are poorly understood. It is crucial to obtain more knowledge on moss and lichen VOCs to improve ecosystem VOC emission models. This is especially relevant at high latitudes, where mosses and lichens are abundant and VOC emissions are expected to increase in response to climate change. In this study, we examined VOC emissions from four common moss (Hylocomium splendens, Pleurozium schreberi, Sphagnum warnstorfii, and Tomentypnum nitens) and lichen (Cladonia arbuscula, Cladonia mitis, Cladonia pleurota, and Nephroma arcticum) species in the Subarctic using gas chromatography-mass spectrometry (GC-MS) and proton-transfer-reaction time-of-flight mass spectrometry. Moss and lichen VOC emissions were dominated by low molecular weight (LMW) VOCs, such as acetone and acetaldehyde, as well as hydrocarbons (HCs) and oxygenated VOCs (oVOCs). Of the studied mosses, S. warnstrofii had the highest and H. splendens had the lowest total VOC emission rates. The VOC emission blends of P. schreberi, S. warnstrofii, and T. nitens were clearly distinct from one another. Of the lichens, N. arcticum had a different VOC blend than the Cladonia spp. N. arcticum also had higher emission rates of HCs, oVOCs, and other GC-MS-based VOCs, but lower LMW VOC emission rates than the other lichen species. Our study demonstrates that mosses and lichens emit considerable amounts of various VOCs and that these emissions are species dependent.

The effect of lichen secondary metabolites on Aspergillus fungi

A systematic review of literature data on the antifungal potential of extracted lichen compounds and individual secondary metabolites against mold species of the genus Aspergillus is provided. Crude extracts from 49 epiphytic, 16 epigeic and 22 epilithic species of lichens and 44 secondary metabolites against 10 species, Aspergillus candidus, A. flavus, A. fumigatus, A. nidulans, A. niger, A. ochraceus, A. parasiticus, A. restrictus, A. stellatus and A. ustus, were analysed. Several measuring techniques were employed for such analyses. Lichen substances were extracted with alcoholic and other organic solvents mainly using the Soxhlet apparatus. Among the three most-studied mold species, the results showed that the crude extracts from the thalli of the lichens Cladonia foliacea, Hypotrachyna cirrhata, Leucodermia leucomelos, Platismatia glauca and Pseudevernia furfuracea against Aspergillus flavus, from C. foliacea, Nephroma arcticum and Parmelia sulcata against A. fumigatus and from Evernia prunastri, Hypogymnia physodes, Umbilicaria cylindrica and Variospora dolomiticola against A. niger have the greatest antifungal potential. The lichen secondary metabolites showed a higher inhibitory potential, e.g. protolichesterinic acid against A. flavus, lecanoric acid against A. fumigatus and orsellinic acid against A. niger; the other seven species of Aspergillus have been poorly studied and require further investigation. A comparison of the inhibitory potential of the tested mixtures of lichen substances and their secondary metabolites shows that they can compete with commonly used antifungal substances, such as ketoconazole and clotrimazole against A. flavus, A. nidulans, A. niger and A. parasiticus and fluconazole in the case of A. fumigatus.

Photosynthesis measurements on the upper and lower side of the thallus of the foliose lichen Nephroma arcticum (L.) Torss

The measurements of chlorophyll fluorescence play an important role in studies of lichen physiology. Usually, for foliose lichens fluorescence kinetics is recorded from the upper thalline side often exhibiting green color reflecting the presence of photosynthetic pigments. The lower side of such lichens is grey, dark-brown or black. At the first time, we evaluated photosynthetic activity distribution by chlorophyll fluorescence analysis on both lower and upper thallus sides for the foliose lichen Nephroma arcticum. We have demonstrated that photosynthesis proceeds not only on the green-colored upper side, but also on the gray lower side of the curled growing edges of the thallus lobes. These sides were differed in terms of PSII photochemical quantum yield, activity of non-regulatory dissipation and non-photochemical quenching of excited chlorophyll states (NPQ). Upper side was characterized by higher maximal PSII efficiency, whereas the lower one of the curled edges was characterized by higher actual photochemical quantum yield during actinic light acclimation. NPQ was higher on the upper surface, whereas, on the lower side (of the curled edges) non-regulatory dissipation was predominant. In terms of photosynthetic activity measurements, these results show, that actinic and measuring light reached the layer of phycobiont despite its shielding by mycobiont hyphae. On the melanized lower side in the basal thalline zone attached to the substratum photosynthesis was not detected. Lower side demonstrated higher level of light scattering in the reflectance spectra. We believe that different photoprotective mechanisms against high light are crucial on the upper and lower sides: NPQ on the upper surface, and light scattering and shielding by mycobiont on the lower side. Possible biological role of photosynthesis on the lower side is discussed.

Распределение микотоксинов в цианолишайниках на побережье Белого моря

In the lichen thalli of 6 Peltigera species and Nephroma arcticum enzyme-linked immunosorbent assay was conducted to investigate the distribution of low-molecular biologically active metabolites related to the group of mycotoxins, as well as the distribution of usnic acid at N. arcticum. Thirteen of micotoxins have been founds in the lichens. Qualitative composition of mycotoxins varies in different species of Peltigera and P. aphthosa, collected in different years. Some mycotoxins showed statistically significant differences of their content in theand lower parts of the thalli of 4 Peltigera species and Nephroma arcticum. The trend of higher accumulation of mycotoxins in the lower older part of the thalli as compared with the younger ones was noted. Statistically reliable data on the higher usnic acid content in the younger of the thallus of N. arcticum as compared with the older was obtained.

Reprint of Efficient fungal UV-screening provides a remarkably high UV-B tolerance of photosystem II in lichen photobionts

Lichen photobionts in situ have an extremely UV-B tolerant photosystem II efficiency (Fv/Fm). We have quantified the UV-B-screening offered by the mycobiont and the photobiont separately. The foliose lichens Nephroma arcticum and Umbilicaria spodochroa with 1: intact or 2: removed cortices were exposed to 0.7 Wm-2 UV-BBE for 4 h. Intact thalli experienced no reduction in Fv/Fm, whereas cortex removal lowered Fv/Fm in exposed photobiont layers by 22% for U. spodochroa and by 14% for N. arcticum. We also gave this UV-B dose to algal cultures of Coccomyxa and Trebouxia, the photobiont genera of N. arcticum and U. spodochroa, respectively. UV-B caused a 56% reduction in Fv/Fm for Coccomyxa, and as much as 98% in Trebouxia. The fluorescence excitation ratio (FER) technique comparing the fluorescence from UV-B or UV-A-excitation light with blue green excitation light using a Xe-PAM fluorometer showed that these photobiont genera did not screen any UV-B or UV-A The FER technique with a Multiplex fluorometer estimated the UV-A screening of isolated algae to be 13–16%, whereas intact lichens screened 92–95% of the UV-A. In conclusion, the cortex of N. arcticum and U. spodochroa transmitted no UV-B and little UV-A to the photobiont layer beneath. Thereby, the upper lichen cortex forms an efficient fungal solar radiation screen providing a high UV-B tolerance for studied photobionts in situ. By contrast, isolated photobionts have no UV-B screening and thus depend on their fungal partners in nature.

Efficient fungal UV-screening provides a remarkably high UV-B tolerance of photosystem II in lichen photobionts

Lichen photobionts in situ have an extremely UV-B tolerant photosystem II efficiency (Fv/Fm). We have quantified the UV-B-screening offered by the mycobiont and the photobiont separately. The foliose lichens Nephroma arcticum and Umbilicaria spodochroa with 1: intact or 2: removed cortices were exposed to 0.7 Wm-2 UV-BBE for 4 h. Intact thalli experienced no reduction in Fv/Fm, whereas cortex removal lowered Fv/Fm in exposed photobiont layers by 22% for U. spodochroa and by 14% for N. arcticum. We also gave this UV-B dose to algal cultures of Coccomyxa and Trebouxia, the photobiont genera of N. arcticum and U. spodochroa, respectively. UV-B caused a 56% reduction in Fv/Fm for Coccomyxa, and as much as 98% in Trebouxia. The fluorescence excitation ratio (FER) technique comparing the fluorescence from UV-B or UV-A-excitation light with blue green excitation light using a Xe-PAM fluorometer showed that these photobiont genera did not screen any UV-B or UV-A The FER technique with a Multiplex fluorometer estimated the UV-A screening of isolated algae to be 13–16%, whereas intact lichens screened 92–95% of the UV-A. In conclusion, the cortex of N. arcticum and U. spodochroa transmitted no UV-B and little UV-A to the photobiont layer beneath. Thereby, the upper lichen cortex forms an efficient fungal solar radiation screen providing a high UV-B tolerance for studied photobionts in situ. By contrast, isolated photobionts have no UV-B screening and thus depend on their fungal partners in nature.

Glacial-relict symptoms in the Western Carpathian flora

Glacial relicts have been regionally more common in glacial than in recent times. A rigorous assessment of which species are indeed glacial relicts is extremely difficult because direct evidence is untraceable or equivocal for many species. We aimed to identify species of the Western Carpathian flora (vascular plants, bryophytes and terrestrial lichens) that display apparent biogeographical and ecological symptoms, suggesting a wider regional or supra-regional distribution during glacial times, or at least before the middle-Holocene climate optimum. We worked with the premise that exemplary relict species should tolerate continental and/or arctic climates, should have large distribution ranges with disjunctions, being regionally rare and ecologically conservative nowadays, should be associated with habitats that occurred during glacial times (tundra, steppe, peatland, open coniferous forest) and should display a restriction of ecological niches in the study region. The assessed species were primarily those with boreo-continental or artcic-alpine distribution. We demonstrated a conspicuous gradient of glacial-relict symptoms, with Carex vaginata, Betula nana, Trichophorum pumilum, Nephroma arcticum, Saxifraga hirculus and Cladonia stellaris topping the ranking. Based on the arbitrary ranking, 289 taxa can be considered high-probability relicts. For only a minority of them, there are any phylogeographical and/or palaeoecological data available from the study area. Biogeographical and ecological symptoms of 144 taxa suggest that they retreated rapidly after the Last Glacial Maximum whereas other species probably retreated later. The first principal component of biogeographical symptoms sorted species from circumpolar arctic-alpine species of acidic peatlands and wet tundra to strongly continental species of steppe, steppe-tundra and mineral-rich fens. This differentiation may mirror the altitudinal zonation of glacial vegetation in the Western Carpathians.

Erratum to: “Bacterial Complexes of Khibiny Mountains Lichens Revealed in Cladonia uncialis, C. portentosa, Alectoria ochroleuca, and Nephroma arcticum” [Microbiology 87, 79 (2018)

Erratum to: “Bacterial Complexes of Khibiny Mountains Lichens Revealed in Cladonia uncialis, C. portentosa, Alectoria ochroleuca, and Nephroma arcticum” [Microbiology 87, 79 (2018)

Bacterial complexes of Khibiny Mountains lichens revealed in Cladonia uncialis, C. portentosa, Alectoria ochroleuca, and Nephroma arcticum

Fluorescence in situ hybridization was used to investigate microbial communities of four lichen species collected in the Murmansk province. The maximal bacterial abundance was shown to depend on both the lichen species and the part of the thallus. Predominant groups of bacteria were revealed: Proteobacteria, Acidobacteria, and Actinobacteria. Criteria for assessment the facultative and obligatory presence of bacteria in lichen microbial communities were established, and approaches to classification of the lichen microbial communities were proposed based on the interdependence of various bacterial groups.

Metabolites of toxigenic fungi in lichens of genera Nephroma, Peltigera, Umbilicaria, and Xanthoria

The component composition of mycotoxin complexes is characterized in foliose lichens of the genera Nephroma, Peltigera, Umbilicaria, and Xanthoria. The interspecies differences in the genus Peltigera are expressed by the number of metabolites detected, from seven in P. aphthosa to three in P. canina, P. didactyla, P. praetextata, and P. rufescens. In Nephroma arcticum eight mycotoxins occurred regularly, with mycophenolic acid in especially high quantities in comparison with other lichens. In Umbilicaria, of six permanent components the content of alternariole is the highest, and in Xanthoria the content of emodine is the highest. Variation of the quantitative content of mycotoxins in general and of species of lichens is discussed, as is expansion of the background spectrum of these metabolites in collections from different territories.

Determination of elemental baseline using peltigeralean lichens from Northeastern Canada (Québec): Initial data collection for long term monitoring of the impact of global climate change on boreal and subarctic area in Canada

Northeastern Canada is mostly free of anthropogenic activities. The extent to which this territory has been impacted by anthropogenic atmospheric depositions remains to be studied. The main goal of our study was to establish background levels for metals in boreal muscicolous/terricolous macrolichens over non-urbanized areas of northeastern Canada (Québec). Concentrations of 18 elements (Na, Mg, Al, P, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Cd, and Pb) were determined for three species of the genus Peltigera (Peltigera aphthosa (L.) Willd. s.l., Peltigera neopolydactyla (Gyeln.) Gyeln. s.l., Peltigera scabrosa Th. Fr. s.l.), and Nephroma arcticum (L.) Torss., along a 1080km south–north transect and along a of 730km west–east transect. We report that elemental contents in the sampled lichen thalli are very low and similar to background levels found in other studies performed in pristine places (high elevation or remote ecosystems) throughout the world.Overall, our results demonstrate that most of the boreal and subarctic zone of Québec (northeastern Canada) is still pristine. The elemental baseline established in these lichen populations will contribute to monitor metal pollution in boreal and sub-polar ecosystems due to global climate change and future industrial expansion.

Distribution of mycotoxins and usnic acid in the thalli of epigeous lichens

The distribution of mycotoxins anc unic acid in the thallus of epigenous fruticose lichens Alectoria ochroleuca; several species of the genera Cladonia, Cotraria, and Flavocetraria; foliose lichens Nephroma arcticum; and six species of the genus Peltigera were studied by mnzyme-linked immunosorbent assay. The mycotoxin content was lower in the top or apical parts of the thalli than in the basal parts and in dead areas. Differences in the distribution of usnic acid were insignificant in the majority of species, but in Cladonia stellaris and N. arcticum lichens the content of this metabolite in the upper and pc ripheral areas was higher than in the basal parts.

Opegrapha bryoriaesp. nov. and Other Lichenicolous Fungi from Asian Russia

Abstract: Zhurbenko, M. P. & Vershinina, S. E. 2014. Opegrapha bryoriae sp. nov. and other lichenicolous fungi from Asian Russia. — Herzogia 27: 93–109. Thirty three species of lichenicolous fungi are reported from Asian Russia. Opegrapha bryoriae sp. nov. (on Bryoria capillaris) is introduced. Presumably new species of Cercidospora (on Cladonia pyxidata), Endococcus (on Evernia esorediosa), Lichenopeltella (on Nephroma arcticum) and Xenonectriella (on Nephroma helveticum) are informally described, illustrated and discussed. Emended descriptions and illustrations of poorly known species Endococcus tricolorans, Phaeospora arctica and Polycoccum superficiale are provided. Lichenopeltella cetrariicola, L. lobariae and Pseudoseptoria usneae are reported new to Asia and Russia; Endococcus tricolorans and Polycoccum superficiale are new to Asia; Clypeococcum hypocenomycis and Cornutispora lichenicola are new to Asian Russia. Cetraria is reported as new host genus for Phaeospora arctica, Nephroma for Lichenopelt...

Recent literature on lichens—217

Abbott, B. F. M. 2009. Checklist of the Lichens and Lichenicolous Fungi of Greece. Bibliotheca Lichenologica No. 103. J. Cramer in der Gebruder Borntraeger Verlagsbuchhandlung. Berlin and Stuttgart. 368 pages. [Exhaustive catalog of Greek lichens based on both literature records and unpublished specimens. Includes extensive listings of synonyms and Greek place names.] Abonyi, D. O., M. U. Adikwu, C. O. Esimone & E. C. Ibezim. 2009. Plants as sources of antiviral agents. African Journal of Biotechnology 8(17): 3989–3994. [Lichens are mentioned as one of the many plant sources.] Ahti, T. 2009. A tribute to John Walter Thomson (1913–2009). Lichenologist 41(6): 561–563. [Short article remembering his life and work, especially on arctic lichens.] Allen, A. & B. Hilton. 2010. [Review] C. W. Smith, A. Aptroot, B. J. Coppins, A. Fletcher, O. L. Gilbert, P. W. James & P. A. Wolseley (eds.). The Lichens of Great Britain and Ireland. The British Lichen Society, Botany Department, Natural History Museum, London. x + 1046 pages. 2009. Lichenologist 42(1): 123–125. Alstrup, V., J. Kocourkova, M. Kukwa, J. Motiejūnaitė, W. Von Brackel & A. Suija. 2009. The lichens and lichenicolous fungi of South Greenland. Folia Cryptogamica Estonica 46: 1–24. [Notes on 744 lichens, 156 lichenicolous and 6 allied fungi. Many species new to Greenland. New: Naetrocymbe kentrospora (Branth) Alstrup comb. nov.] ——— & U. Sochting. 2009. Galloea cladoniicola, a new hyphomycetous lichenicolous fungus from Denmark. Graphis Scripta 21(2): 33–35. [New: Galloea cladoniicola gen. et sp. nov.] Aptroot, A. 2009. A revision of the lichen genus Stirtonia. Lichenologist 41(6): 615–625. [Treatment of 13 species; key. Stirtonia neotropica (Netherlands Antilles), S. schummii (Seychelles) and S. curvata Aptroot spp. nov. (Indonesia).] ———. 2009. Diversity and endemism in the pyrenocarpous lichen families Pyrenulaceae and Trypetheliaceae in the Malesian flora region. Blumea 54(1–3): 145–147. [‘‘Species numbers in both families seem highest in Australia and Papua New Guinea, but some potentially rich regions are much undercollected. The numbers of local endemics are also highest in these areas, at least in the Pyrenulaceae, and remarkably high for lichens.’’] Armaleo, D. & S. May. 2009. Sizing the fungal and algal genomes of the lichen Cladonia grayi through quantitative PCR. Symbiosis 49(1): 43–51. [Authors report first genome size for a lichen, 28.6 Mb (mycobiont) and 106.7 Mb (Asterochloris photobiont). DNA was obtained from culture of soredia.] Armstrong, R. A. & S. N. Smith. 2009. Carbohydrates in the hypothallus and aerolae of the crustose lichen Rhizocarpon geographicum (L.) DC. Symbiosis 42(2): 95–100. [Lichen material from Wales. Authors report 8 carbohydrates present. The results suggest that the ‘‘ ... hypothallus has a lower demand for carbohydrates than the areolae or there is limited transport ...’’ and the ‘‘ ... increased trehalose in the non-lichenised hypothallus may be an adaptation to withstand stress and desiccation ....’’] Asplund, J. & Y. Gauslaa. 2010. The gastropod Arion fuscus prefers cyanobacterial to green algal parts of the tripartite lichen Nephroma arcticum due to low chemical defense. Lichenologist 42(1): 113–117. [Gastropods in experiments preferred cephalodia which lack secondary lichen metabolites. This feeding behavior reduces N concentration 1 Author e-mail: regan@unomaha.edu The cumulative database for this series is available in searchable form on the World Wide Web at http:// www.nhm.uio.no/botanisk/bot-mus/lav/sok_rll.htm. I owe special thanks to Bill Buck for providing copies of papers by other authors, which were otherwise unavailable to me, and to the cooperating authors who send reprints or electronic versions of their works to me for inclusion in this series. DOI: 10.1639/0007-2745-113.2.390

The gastropod Arion fuscus prefers cyanobacterial to green algal parts of the tripartite lichen Nephroma arcticum due to low chemical defence

AbstractAlthough the tripartite terricolous lichen Nephroma arcticum is easily accessible to lichen-feeding gastropods, grazing marks are mainly restricted to localized cephalodia with N-fixing Nostoc. We tested if this gastropod preference for cephalodia can be explained by differences in carbon based secondary compounds (CBSCs) in cyanobacterial versus green-algal tissues. CBSCs were non-destructively removed from air-dry thalli by 100% acetone. Compound deficient and control thallus parts were offered to the slug Arion fuscus and grazing preferences were quantified by area measurements in ArcGIS™. The concentrations of CBSCs (phenarctin, usnic acid, nephroarctin and methyl gyrophorate) in thallus parts with and without cephalodia were quantified with HPLC. Compared to purely green-algal parts, cephalodial parts with adjoining fungal tissues contained less defensive compounds, and were preferred by A. fuscus. The cephalodia themselves do not contain any CBSCs. After acetone rinsing, A. fuscus did not discriminate between green-algal and cyanobacterial parts. The results were consistent with the hypothesis that CBSCs in green-algal parts of N. arcticum play a herbivore-defensive role. It is further hypothesized that grazing of cephalodia may lead to N-starvation and reduced growth of N. arcticum thalli in southern portions of its range where lichenivorous gastropods are more abundant. This may play a role in shaping the southern distribution limit of this arctic-boreal lichen species.

A comparison of the physiology, anatomy and ribosomal DNA in alpine and subalpine populations of the lichen Nephroma arcticum—the effects of an eight-year transplant experiment

Thalli of Nephroma arcticum were transplanted between and within a high-elevation alpine heath (1100 m) and a low-elevation subalpine mountain birch forest (380 m) in northern Swedish Lapland and harvested after eight years. Statistically significant differences (P < 0.05) were found between control samples for dark respiration rates, photon use efficiencies (apparent quantum yields) and light compensation points (all were higher in the high-altitude population). The following traits were significantly affected by transplanting: (1) epicortex thickness, (2) upper cortex thickness in the low-altitude population, (3) maximum photosynthetic rates, (4) dark respiration rates and (5) light compensation point. Of these malleable traits, all reduce the differences between the controls although there seems to be over-compensation in maximum net photosynthesis and under-compensation in dark respiration rate of the low-altitude population. Conservative traits, i.e., those that did not change significantly with transplantation were: (1) thallus thickness, (2) algal layer thickness, (3) algal cell diameter and (4) light saturation level. Small, yet significant differences in anatomy and physiology suggest that an ecotypic differentiation was established although the two internal transcribed DNA spacers ITS 1 and ITS 2 showed no corresponding variation between the populations.

Классификация бореальных лесов севера Европейской России. I. Олиготрофные хвойные леса

Results of a syntaxonomical study of the oligotrophic forests of northern European Russia are presented. The main forest types have been classified into 2 orders of the class Vaccinio-Piceetea, 4 alliances, 6 associations and 1 community. The new alliance Empetro-Piceion all. nov., which includes zonal spruce and birch northern forest association Empetro-Piceetum, has been established. These communities are formed according to cold temperature and high (sometimes temporarily) soil moisture and are characterized by the lower tree canopy, mosaic herb and moss-lichen layers with boreal mosses, sphagnum and lichens. In the middle taiga subzone these communities are replaced by Eu-Piceetum myrtilletosum. The forests with lichens are referred to order Cladonio-Vaccinietalia and divided into 4 associations. Lichen pine forests of the north-west of boreal zone were described as ass. Flavocetrario nivalis—Pinetum ass. nov. This association with a great number of lichens is differentiated by Cladonia arbuscula subsp. mitis, Flavocetraria nivalis, Cetraria ericetorum, Stereocaulon grande, Dicranum fuscescens, D. drummondii, Nephroma arcticum and species of Cladonia. The ass. Cadonio arbusculae—Pinetum (Caj. 1921) K.-Lund 1967 contains lichen pine forests with lower number of lichens and is distributed mostly in middle part of the taiga zone. The spruce-pine forests with mixed moss-lichen cover correspond to ass. Vaccinio-Pinetum. Ass. Hedysaro-Laricetum represents rich and well differentiated larch forests in the east of European Russia.

Growth in two foliose tripartite lichens, Nephroma arcticum and Peltigera aphthosa : empirical modelling of external vs internal factors

Summary 1 To assess how internal and external factors contribute to lichen growth, light, water and nutrient supplies were manipulated during 3 months in the field for the lichens Nephroma arcticum (L.) Torss. and Peltigera aphthosa (L.) Willd. Concomitant measures of weight and area gain, microclimatic conditions and investments in photobiont vs mycobiont tissue were also conducted. 2 In both lichens ≈80% of the variation in weight gain was explained by a linear regression model including light received during wet active periods, chlorophyll a concentration and area gain. All three parameters had a positive effect on weight gain. 3 About 80% of the variation in area gain was explained by a model including variation in weight gain, initial thallus specific weight, ergosterol and chitin concentration. The model was identical for the two lichens, with a positive effect of weight gain and thallus specific weight and a negative effect of ergosterol and chitin. 4 Peltigera aphthosa grew faster than N. arcticum when exposed to the same environmental conditions. This could be explained by its higher chlorophyll a to ergosterol ratio, and a greater water-holding capacity prolonging the active time in light.

Growth, nitrogen uptake, and resource allocation in the two tripartite lichens Nephroma arcticum and Peltigera aphthosa during nitrogen stress

Summary Lichen responses towards nitrogen stress, both increased exposure and deprivation of N, were investigated by measuring N uptake, growth, ergosterol, chitin and Chla in two tripartite nitrogen‐fixing species, Nephroma arctium and Peltigera aphthosa. The lichens were irrigated with different N forms, enriched in 15N to assess N uptake, during 3 months in the field, with a total N dosage of 500 mg m−2. Nitrogen deprivation was induced by removing the nitrogen‐fixing cephalodia. The lichens took up 11–134 mg N m−2 of the added N, corresponding to 1–4% of their total thallus N. Uptake was 4 times higher for NH4+ than for NO3−, and the highest 15N concentrations were found in newly synthesized tissue. Both forms of N stress affected thallus expansion rates in both species. It is concluded that the two lichens were able to maintain a balanced tissue N concentration despite large variations in N supply, and that assimilated N might be transported to growing apices. Alternatively, N assimilation from external sources might be greater in the margins than in the mature thallus. Thallus expansion was sensitive to N stress, apparently being tightly coupled to N assimilation.

The effect of nitrogen on growth and key thallus components in the two tripartite lichens, Nephroma arcticum and Peltigera aphthosa

ABSTRACTRelationships between growth, nitrogen and concentration of unique biont components were investigated for the tripartite lichens Nephroma arcticum (L.) Torss. and Peltigera aphthosa (L.) Willd. Nitrogen availability was manipulated during 4 summer months by removing cephalodia and their associated N2 fixation activity, or by weekly irrigation with NH4NO3. Chlorophyll and ribulose 1·5‐biphosphate carboxylase/oxygenase (Rubisco), and chitin and ergosterol were used as photobiont and mycobiont markers, respectively. Nitrogen concentrations were similar in older and newer parts of the same thallus, varying between 2 and 5 g m−2, with P. aphthosa having higher concentrations than N. arcticum. Both chlorophyll (Chl a) and chitin were linearly correlated with thallus N, but N. arcticum invested more in fungal biomass and had lower Chl a concentrations in comparison with P. aphthosa at equal thallus N. During the 4 months, control and N‐fertilized thalli of N. arcticum increased in area by 0·2 m2 m−2 and P. aphthosa by 0·4 m2 m−2. Thallus expansion was significantly inhibited in samples without cephalodia, but there was no effect on lichen weight gain. Mean relative growth rate (RGR; mg g−1 d−1) was 3·8 for N. arcticum and 8·4 for P. aphthosa, when time (d) reflected the lichen wet periods. RGR was 2–3 times lower when based on the whole time, i.e. when including dry periods. The efficiency (e) of converting incident irradiance into lichen biomass was positively and linearly correlated with thallus Chl a concentration to the same extent in both species. The slower growth rates of N. arcticum, in comparison with P. aphthosa, could then be explained by their lower nitrogen and Chl a concentrations and a subsequently lower light energy conversion efficiency. Functional and dynamic aspects of resource allocation patterns of the two lichens are discussed in relation to the above findings.