Cyanolichens can have both cyanobacteria and green algae in a common layer as major contributors to photosynthesis

Background and Aims

Cyanolichens are usually stated to be bipartite (mycobiont plus cyanobacterial photobiont). Analyses revealed green algal carbohydrates in supposedly cyanobacterial lichens (in the genera Pseudocyphellaria, Sticta and Peltigera). Investigations were carried out to determine if both cyanobacteria and green algae were present in these lichens and, if so, what were their roles.

Methods

The types of photobiont present were determined by light and fluorescence microscopy. Small carbohydrates were analysed to detect the presence of green algal metabolites. Thalli were treated with selected strengths of Zn²⁺ solutions that stop cyanobacterial but not green algal photosynthesis. CO₂ exchange was measured before and after treatment to determine the contribution of each photobiont to total thallus photosynthesis. Heterocyst frequencies were determined to clarify whether the cyanobacteria were modified for increased nitrogen fixation (high heterocyst frequencies) or were normal, vegetative cells.

Key Results

Several cyanobacterial lichens had green algae present in the photosynthetic layer of the thallus. The presence of the green algal transfer carbohydrate (ribitol) and the incomplete inhibition of thallus photosynthesis upon treatment with Zn²⁺ solutions showed that both photobionts contributed to the photosynthesis of the lichen thallus. Low heterocyst frequencies showed that, despite the presence of adjacent green algae, the cyanobacteria were not altered to increase nitrogen fixation.

Conclusions

These cyanobacterial lichens are a tripartite lichen symbiont combination in which the mycobiont has two primarily photosynthetic photobionts, ‘co-primary photobionts’, a cyanobacterium (dominant) and a green alga. This demonstrates high flexibility in photobiont choice by the mycobiont in the Peltigerales. Overall thallus appearance does not change whether one or two photobionts are present in the cyanobacterial thallus. This suggests that, if there is a photobiont effect on thallus structure, it is not specific to one or the other photobiont.     

Population structure of mycobionts and photobionts of the widespread lichen Cetraria aculeata

Lichens are symbioses between fungi (mycobionts) and photoautotrophic green algae or cyanobacteria (photobionts). Many lichens occupy large distributional ranges covering several climatic zones. So far, little is known about the large‐scale phylogeography of lichen photobionts and their role in shaping the distributional ranges of lichens. We studied south polar, temperate and north polar populations of the widely distributed fruticose lichen Cetraria aculeata. Based on the DNA sequences from three loci for each symbiont, we compared the genetic structure of mycobionts and photobionts. Phylogenetic reconstructions and Bayesian clustering methods divided the mycobiont and photobiont data sets into three groups. An amova shows that the genetic variance of the photobiont is best explained by differentiation between temperate and polar regions and that of the mycobiont by an interaction of climatic and geographical factors. By partialling out the relative contribution of climate, geography and codispersal, we found that the most relevant factors shaping the genetic structure of the photobiont are climate and a history of codispersal. Mycobionts in the temperate region are consistently associated with a specific photobiont lineage. We therefore conclude that a photobiont switch in the past enabled C. aculeata to colonize temperate as well as polar habitats. Rare photobiont switches may increase the geographical range and ecological niche of lichen mycobionts by associating them with locally adapted photobionts in climatically different regions and, together with isolation by distance, may lead to genetic isolation between populations and thus drive the evolution of lichens.     

Water status related photosynthesis and carbon isotope discrimination in species of the lichen genusPseudocyphellaria with green or blue-green photobionts and in photosymbiodemes

Summary Green lichens have been shown to attain positive net photosynthesis in the presence of water vapour while blue-green lichens require liquid water (Lange et al. 1986). This behaviour is confirmed not only for species with differing photobionts in the genusPseudocyphellaria but for green and blue-green photobionts in a single joined thallus (photosymbiodeme), with a single mycobiont, and also when adjacent as co-primary photobionts. The different response is therefore a property of the photobiont. The results are consistent with published photosynthesis/water content response curves. The minimum thallus water content for positive net photosynthesis appears to be much lower in green lichens (15% to 30%, related to dry weight) compared to blue-greens (85% to 100%). Since both types of lichen rehydrate to about 50% water content by water vapour uptake only green lichens will show positive net photosynthesis. It is proposed that the presence of sugar alcohols in green algae allow them to retain a liquid pool (concentrated solution) in their chloroplasts at low water potentials and even to reform it by water vapour uptake after being dried. The previously shown difference in δ¹³C values between blue-green and green lichens is also retained in a photosymbiodeme and must be photobiont determined. The wide range of δ¹³C values in lichens can be explained by a C₃ carboxylation system and the various effects of different limiting processes for photosynthetic CO₂ fixation. If carboxylation is rate limiting, there will be a strong discrimination of¹³CO₂, at high internal CO₂ partial pressure. The resulting very low δ¹³C values (-31 to-35‰) have been found only in green lichens which are able to photosynthesize at low thallus water content by equilibraiton with water vapour. When the liquid phase diffusion of CO₂ becomes more and more rate limiting and the internal CO₂ pressure decreases, the¹³C content of the photosynthates increases and less negative δ¹³C values results, as are found for blue-green lichens.     

Gas exchange and carbon isotope discrimination in lichens: Evidence for interactions between CO2-concentrating mechanisms and diffusion limitation

The characteristics of gas exchange and carbon isotope discrimination were determined for a number of lichen species, representing contrasting associations between fungal (mycobiont) and photosynthetic (photobiont) organism. These parameters were evaluated with regard to the occurrence of any CO₂-concentrating mechanism (CCM) expressed specifically by the green algal (phycobiont) or cyanobacterial (cyanobiont) partner. Carbon isotope discrimination () fell into three categories. The highest , found in lichens comprising a phycobiont plus cyanobacteria limited to pockets in the thallus (known as cephalodia), ranged from 24 to 28, equivalent to a carbon isotope ratio (¹³C) of around -32 to-36 vs. Pee Dee Belemnite (PDB) standard. Further evidence was consistent with CO₂ supply to the carboxylating system entirely mediated by diffusion rather than a CCM, in that thallus CO₂ compensation point and online instantaneous were also high, in the range normally associated with C₃ higher plants. For lichens consisting of phycobiont or cyanobiont alone, organic material formed two distinct ranges around 15 (equivalent to a ¹³C of -23%.). Thallus compensation point and instantaneous were lower in the cyanobiont group, which also showed higher maximum rates of net photosynthesis, whether expressed on the basis of thallus dry weight, chlorophyll content or area. These data provide additional evidence for the activity of a CCM in cyanobiont lichens, which only show photosynthetic activity when reactivated with liquid water. Rates of net CO₂ uptake were lower in both phycobiont associations, but were relatively constant across a wide working range of thallus water contents, usually in parallel with on-line . The phycobiont response was consistent whether photosynthesis had been reactivated with liquid water or water vapour. The effect of diffusion limitation could generally be seen with a 3–4 decrease in instantaneous at the highest water contents. The expression of a CCM in phycobiont algae, although reduced compared with that in cyanobacteria, has already been related to the occurrence of pyrenoids in chloroplasts. In view of the inherent requirement of cyanobacteria for some form of CCM, and the smaller pools of dissolved inorganic carbon (DIC = CO₂ + HCO _inf3 ^su– + CO _inf3 ^su2– ) associated with phycobiont lichens, it appears that characteristics provide a good measure of the magnitude of any CCM, albeit tempered by diffusion limitation at the highest thallus water contents.Abbreviations ANOVA analysis of variance - CCM CO₂-concentrating mechanism - cyanobiont cyanobacterium - DIC CO₂ + HCO _inf3 ^su– + CO _inf3 ^su2– (dissolved inorganic carbon) - photobiont photosynthetic organism present in the association - phycobiont green alga - phycobiont + cephalodia green algae + cyanobacteria in cephalodia - Pmax maximum photosynthetic rate - PPFD photosynthetic photon flux density, 400–700 nm - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase - carbon isotope discrimination () - ¹³C carbon isotope ratio () We would like to thank Dr. Enrico Brugnoli (CNR, Porano, Italy) and E.C. Smith (University of Newcastle) for many helpful discussions. Dr. Kristin Palmqvist (Department of Plant Physiology, University of Umeå, Sweden) kindly provided the samples of Peltigera apthosa. In particularly, Cristina Máguas would like to thank to Prof. Fernando Catarino (University of Lisbon) for his support throughout this study. Cristina Máguas has been supported by JNICT-Science Programme studentship (BD/153/90-RN).     

Spatial patterns of photobiont diversity in some Nostoc-containing lichens

Patterns of photobiont diversity were examined in some Nostoc -containing lichens using the nucleotide sequence of the cyanobacterial tRNA^Leu (UAA) intron. Lichen specimens collected in northwestern USA were analysed and the sequence data were compared with tRNA^Leu(UAA) intron sequences previously obtained from lichens in northern Europe. Generally, it is the species identity of a lichen rather than the geographical origin of the specimen that determines the identity of the cyanobiont. Identical intron sequences were found in Peltigera membranacea specimens collected in Oregon (USA) and in Sweden, and very similar sequences were also found in Nephroma resupinatum thalli collected in Oregon and Finland. Furthermore, in mixed assemblages where two Peltigera species grew in physical contact with each other, the different lichen species housed different photobiont strains. There is however not a one-to-one relation between mycobiont and photobiont as some intron sequences were found in more than one lichen species, and different intron sequences were found in different samples of some lichen taxa. Peltigera venosa exhibited a higher level of photobiont diversity than any other lichen species studied, and several intron sequences could for the first time be obtained from a single thallus. It is not clear whether this is evidence of lower cyanobiont specificity, or reflects an ability to exhibit different degrees of lichenization with different Nostoc strains. In one specimen of P. venosa , which contained bipartite cyanosymbiodemes and tripartite, cephalodiate thalli, both thallus types contained the same intron sequence.     

CO2 exchange and thallus nitrogen across 75 contrasting lichen associations from different climate zones

Aiming to investigate whether a carbon-to-nitrogen equilibrium model describes resource allocation in lichens, net photosynthesis (NP), respiration (R), concentrations of nitrogen (N), chlorophyll (Chl), chitin and ergosterol were investigated in 75 different lichen associations collected in Antarctica, Arctic Canada, boreal Sweden, and temperate/subtropical forests of Tenerife, South Africa and Japan. The lichens had various morphologies and represented seven photobiont and 41 mycobiont genera. Chl a, chitin and ergosterol were used as indirect markers of photobiont activity, fungal biomass and fungal respiration, respectively. The lichens were divided into three groups according to photobiont: (1) species with green algae, (2) species with cyanobacteria, and (3) tripartite species with green algal photobionts and cyanobacteria in cephalodia. Across species, thallus N concentration ranged from 1 to 50 mg g^-1 dry wt., NP varied 50-fold, and R 10-fold. In average, green algal lichens had the lowest, cyanobacterial Nostoc lichens the highest and tripartite lichens intermediate N concentrations. All three markers increased with thallus N concentration, and lichens with the highest Chl a and N concentrations had the highest rates of both P and R. Chl a alone accounted for ca. 30% of variation in NP and R across species. On average, the photosynthetic efficiency quotient [K_F=(NP_max+R)/R)] ranged from 2.4 to 8.6, being higher in fruticose green algal lichens than in foliose Nostoc lichens. The former group invested more N in Chl a and this trait increased NP_max while decreasing R. In general terms, the investigated lichens invested N resources such that their maximal C input capacity matched their respiratory C demand around a similar (positive) equilibrium across species. However, it is not clear how this apparent optimisation of resource use is regulated in these symbiotic organisms.     

Thallus initiation and development in the lichen Rhizocarpon lecanorinum

Ascospore germination, thallus initiation, and areole and prothallus development in the lichen Rhizocarpon lecanorinum Anders were examined using light, fluorescence and scanning electron microscopy. The ascospore germ hyphae remain very short and do not form a prothallus-like mycelium. Instead, a compact soredium-like granule develops directly from sporeling contact with a compatible species of Trebouxia . Diffuse initial stages involving non-trebouxioid algae are lacking. The onset of thallus differentiation is marked by the deposition of rhizocarpic acid in an incipient cortical layer within the apical part of the granule. As pigmentation and cortex-formation transform this structure into a typical areole, radiating prothallus hyphae are simultaneously initiated from its basal margin. Most areoles formed subsequently in the marginal prothallus lack subtending melanized hyphae and apparently stem from overgrowth by the prothallus of photobiont cells on, or in, the substratum. Apothecia reach maturity in thalli as small as 2 mm in diameter. It is proposed that the lack of diffuse hyphal growth in sporelings and telescoped morphogenesis of R. lecanorinum are part of a life history strategy geared to precocious, heavy investment in ascospore production. The R. lecanorinum – Trebouxia symbiosis has a number of features which make it well-suited for further studies of the life history and development of prothallus-forming crustose lichens with sexually reproducing mycobionts.     

As thick as three in a bed

During the evolution of the lichen symbiosis, shifts from one main type of photobiont to another were infrequent (Miadlikowska et al. 2006 ) but some remarkable transitions from green algal to diazotrophic cyanobacterial photobionts are known from unrelated fungal clades within the ascomycetes. Cyanobacterial, including tripartite, associations (green algal and cyanobacterial photobionts in one lichen individual) facilitate these holobionts to live as C‐ and N‐autotrophs. Tripartite lichens are among the most productive lichens, which provide N‐fertilization to forest ecosystems under oceanic climates (Peltigerales) or deliver low, but ecologically significant N‐input into subarctic and alpine soil communities (Lecanorales, Agyriales). In this issue of Molecular Ecology, Schneider et al. (2016) mapped morphometric data against an eight‐locus fungal phylogeny across a transition of photobiont interactions from green algal to a tripartite association and used a phylogenetic comparative framework to explore the role of nitrogen‐fixing cyanobacteria in size differences in the Trapelia–Placopsis clade (Agyriales). Within the group of tripartite species, the volume of cyanobacteria‐containing structures (cephalodia) correlates with thallus thickness in both phylogenetic generalized least squares and phylogenetic generalized linear mixed‐effects analyses, and the fruiting body core volume increased ninefold. The authors conclude that cyanobacterial symbiosis appears to have enabled lichens to overcome size constraints in oligotrophic environments such as rock surfaces. The Trapelia–Placopsis clade analyzed by Schneider et al. (2016) is an exciting example of interactions between ecology, phylogeny and lichen biology including development – from thin crustose green algal microlichens to thick placodioid, tripartite macrolichens: as thick as three in a bed (Scott 1820 ).     

Fungal farmers or algal escorts: lichen adaptation from the algal perspective

Domestication of algae by lichen‐forming fungi describes the symbiotic relationship between the photosynthetic (green alga or cyanobacterium; photobiont) and fungal (mycobiont) partnership in lichen associations ( Goward 1992 ). The algal domestication implies that the mycobiont cultivates the alga as a monoculture within its thallus, analogous to a farmer cultivating a food crop. However, the initial photobiont ‘selection’ by the mycobiont may be predetermined by the habitat rather than by the farmer. When the mycobiont selects a photobiont from the available photobionts within a habitat, the mycobiont may influence photobiont growth and reproduction ( Ahmadjian & Jacobs 1981 ) only after the interaction has been initiated. The theory of ecological guilds ( Rikkinen et al. 2002 ) proposes that habitat limits the variety of photobionts available to the fungal partner. While some studies provide evidence to support the theory of ecological guilds in cyanobacterial lichens ( Rikkinen et al. 2002 ), other studies propose models to explain variation in symbiont combinations in green algal lichens ( Ohmura et al. 2006 ; Piercey‐Normore 2006 ; Yahr et al. 2006 ) hypothesizing the existence of such guilds. In this issue of Molecular Ecology, Peksa & ?kaloud (2011) test the theory of ecological guilds and suggest a relationship between algal habitat requirements and lichen adaptation in green algal lichens of the genus Lepraria. The environmental parameters examined in this study, exposure to rainfall, altitude and substratum type, are integral to lichen biology. Lichens have a poikilohydric nature, relying on the availability of atmospheric moisture for metabolic processes. Having no known active mechanism to preserve metabolic thallus moisture in times of drought, one would expect a strong influence of the environment on symbiont adaptation to specific habitats. Adaptation to changes in substrata and its properties would be expected with the intimate contact between crustose lichens in the genus Lepraria. Altitude has been suggested to influence species distributions in a wide range of taxonomic groups. This is one of the first studies to illustrate an ecological guild, mainly for exposure to rainfall (ombrophiles and ombrophobes), with green algal lichens.     

Structural and functional processes during water vapour uptake and desiccation in selected lichens with green algal photobionts

Structural alterations of the photobiont and mycobiont cells of lichens have been related to CO₂-gas exchange during experiments involving water vapour uptake and desiccation of liquid-water-saturated thalli. Increasing water vapour uptake of air dry lichens led to a gradual unfolding of the photobiont cells in Lobaria pulmonaria, Pseudevernia furfuracea, Ramalina maciformis and Teloschistes lacunosus as studied by low-temperature scanning electron microscopy. The data indicated that globular, probably turgid, cells and also slightly infolded or even heavily collapsed cells contributed to positive net photosynthesis, which was reached after water vapour uptake by the four species studied. During desiccation of fully water-saturated thalli of L. pulmonaria, extrathalline water films gradually evaporated before maximum values of CO₂-gas exchange were measured and before photobiont cells started to shrivel. In contrast, in P. furfuracea the CO₂-gas exchange maximum was reached when a considerable percentage of photobiont cells had already collapsed and while other parts of the thalli were still covered with liquid water. Further desiccation led to cavitation of the cortical cells in both species, this occurring at water contents at which net photosynthesis was still positive.Abbreviations EF exoplasmic fracture face - LTSEM low-temperature scanning electron microscopy - NP net photosynthesis - PAR photosynthetic active radiation (400–700 nm) - PF plasmic fracture face We thank D. Pichier, P. Hatvani, H. Müller, Birmensdorf, and J.B. Winkler, Kiel, for technical assistance, and J. Innes, Birmensdorf, for correcting the English text. Stimulating discussion with R. Honegger (Institut für Pflanzenbiologie, Universität Zürich, Switzerland), L. Kappen (Botanisches Institut, Universität Kiel, Germany), T.G.A. Green (Department of Biological Sciences, Hamilton, New Zealand), and O.L. Lange (Julius-von-Sachs-Institut für Biowissenschaften, Universität Würzburg, Germany) are gratefully acknowledged.     

Asymmetric Co-evolution in the Lichen Symbiosis Caused by a Limited Capacity for Adaptation in the Photobiont

It is proposed that lichen photobionts, compared to mycobionts, have very limited capacity to evolve adaptations to lichenization, so that the symbionts in lichens do not co-evolve. This is because lichens have (a) no sequential selection of photobiont cells from one lichen into another needed for Darwinian natural selection and (b) no photobiont sexual reproduction in the thallus. Molecular studies of lichen photobionts indicate no predictable patterns of photobiont lineages that occur in lichens so supporting this proposal. Any adaptation by photobionts accumulating beneficial mutations for lichenization is probably insignificant compared to the rate of mycobiont adaptation. This proposal poses questions for research relating the photobiont sexual cycle (genetic and cellular), the fate of photobiont lineages after lichenization, whether lineages of photobionts in thalli change with time, thallus formation by from spores as well as carbohydrate movement from photobionts to mycobionts and regulation of co-development of the symbionts in the thallus.     

Microclimatic differentiation of gene pools in the Lobaria pulmonaria symbiosis in a primeval forest landscape

Population genetics of the tree‐colonizing lichen Lobaria pulmonaria were studied in the largest primeval beech forest of Europe, covering 10 000 ha. During an intensive survey of the area, we collected 1522 thallus fragments originating from 483 trees, which were genotyped with eight mycobiont‐ and 14 photobiont‐specific microsatellite markers. The mycobiont and photobiont of L. pulmonaria were found to consist of two distinct gene pools, which are co‐existing within small areas of 3–180 ha in a homogeneous beech forest. The small‐scale distribution pattern of the symbiotic gene pools show habitat partitioning of lineages associated with either floodplains or mountain forests. Using approximate Bayesian computation (ABC), we dated the divergence of the two fungal gene pools of L. pulmonaria as the Early Pleistocene. Both fungal gene pools survived the Pleistocene glacial cycles in the Carpathians, although possibly in climatically different refugia. Fungal diversification prior to these cycles and the selection of photobionts with different altitudinal distributions explain the current sympatric, but ecologically differentiated habitat partitioning of L. pulmonaria. In addition, the habitat preferences of the mycobiont are determined by other factors and are rather independent of those of the photobiont at the landscape level. The distinct gene pools should be considered evolutionarily significant units and deserve specific conservation priorities in the future, for example gene pool A, which is a Pliocene relict.     

Prolonging the hydration and active metabolism from light periods into nights substantially enhances lichen growth

This study investigates how hydration during light and dark periods influences growth in two epiphytic old forest lichens, the green algal Lobaria pulmonaria and the cyanobacterial L. scrobiculata. The lichens were cultivated in growth chambers for 14 days (200 μmol m^?1 s^?2; 12 h photoperiod) at four temperature regimes (25/20 °C, 21/16 °C, 13/8 °C, and 6/1 °C; day/night temperatures) and two hydration regimes (12 h day-time hydration; 12 h day-time + 12 h night-time hydration). Growth was highly dynamic, showing that short-term growth experiments in growth cabinets have a high, but largely unexplored potential in functional lichen studies. The highest measured growth rates were not far from the maximal dry matter gain estimated from published net photosynthetic CO₂ uptake data. For the entire data set, photobiont type, temperature, hydration regime and specific thallus mass accounted for 46.6 % of the variation in relative growth rate (RGR). Both species showed substantially higher relative growth rates based on both biomass (RGR) and thallus area (RT_AGR) when they were hydrated day and night compared to hydration in light only. Chronic photoinhibition was substantial in thalli hydrated only during the day time and kept at the highest and lowest temperature regimes, resulting in exponential increases in RGR with increasing maximal PSII efficiency (F _v/F _m) in both species. However, the depression in F _v/F _m was stronger for the cyanolichen than for the cephalolichen at extreme temperatures. The growth-stimulating effect of night-time hydration suggests that nocturnal metabolic activity improves recovery of photoinhibition and/or enhances the conversion rate of photosynthates into thallus extension.     

Climate warming causes photobiont degradation and carbon starvation in a boreal climate sentinel lichen

Premise

The long-term potential for acclimation by lichens to changing climates is poorly known, despite their prominent roles in forested ecosystems. Although often considered “extremophiles,” lichens may not readily acclimate to novel climates well beyond historical norms. In a previous study (Smith et al., 2018), Evernia mesomorpha transplants in a whole-ecosystem climate change experiment showed drastic mass loss after 1 yr of warming and drying; however, the causes of this mass loss were not addressed.

Methods

We examined the causes of this warming-induced mass loss by measuring physiological, functional, and reproductive attributes of lichen transplants.

Results

Severe loss of mass and physiological function occurred above +2°C of experimental warming. Loss of algal symbionts (“bleaching”) and turnover in algal community compositions increased with temperature and were the clearest impacts of experimental warming. Enhanced CO₂ had no significant physiological or symbiont composition effects. The functional loss of algal photobionts led to significant loss of mass and specific thallus mass (STM), which in turn reduced water-holding capacity (WHC). Although algal genotypes remained detectable in thalli exposed to higher stress, within-thallus photobiont communities shifted in composition toward greater diversity.

Conclusions

The strong negative impacts of warming and/or lower humidity on Evernia mesomorpha were driven by a loss of photobiont activity. Analogous to the effects of climate change on corals, the balance of symbiont carbon metabolism in lichens is central to their resilience to changing conditions.     

Spatial organization of the three‐component lichen Peltigera aphthosa in functional terms

The cephalolichen Peltigera aphthosa (L.) Willd. is characterized by lateral heterogeneity, which manifests itself in the presence of three thallus zones, referred to as the apical, basal and medial zone. These zones differ in terms of interaction between lichen bionts and their physiological activity. The apical thallus zone is more efficient in establishing a contact with cyanobacteria, because of a higher lectin content and a larger overall thallus surface area due to the presence of numerous mycobiont hyphae. Cephalodia are formed in this zone. The interaction between the mycobiont and cyanobiont is more intense in the medial zone. However, the establishment of the contact with cyanobacteria in this zone less probable. The spatial distribution of lectins in the thallus was determined. To reveal the differences in photosynthetic activity in three thallus zones, transient analysis of chlorophyll a fluorescence and the assessment of non‐photochemical quenching of excited chlorophyll states were performed. Assimilation of absorbed light energy was more effective in the medial zone. The basal zone was characterized by decreased photosynthetic activity, lichen dissociation and thallus death.     

Externally held water – a key factor for hair lichens in boreal forest canopies

Lichens hold water inside (internal pool) and outside their body (external pool). Yet, external pool size is not known in hair lichens dominating boreal forest canopies. Here we quantify morphological traits and internal/external water in two widespread Bryoria species along Picea abies canopy-height gradients: Bryoria fuscescens at 5–20 m and Bryoria capillaris at 15–20 m. Dry mass and specific thallus mass (STM) of intact B. fuscescens increased with height, while STM of individual branches did not. Maximum water holding capacity (mg H₂O cm⁻²) increased with height, but did not differ between the species. Bryoria had much larger external (79–84% of total) than internal water pools, trapping water by dense clusters of thin, overlapping branches. They thus increase water storage in boreal forest canopies and influence hydrology. High external water storage extends hydration periods and improves lichen performance in upper canopies, and thereby contributes to the success of these hair lichens.     

A Note on the Relationship Between Some Saxicolous Lichens and Manganese Ore in North Wales,UK

Manganese oxyhydroxides have been found deposited on the surface of the lichen Catillaria chalybeia on an altered rhodochrosite. It is suggested that the Mn was mobilised from the ore surface via surface-weathering and redeposited in the thallus. The lichen Acarospora smaragdula also grew upon the ore but showed no sign of Mn deposition. Nine further lichens and two bryophytes were also found on the ore.     

Effects of nutrient amendments on fine root biomass in a primary successional forest in Hawai'i

Summary Thalli of Lobaria pulmonaria (L.) Hoffm., a nitrogen-fixing epiphyte common in mesic temperate forests, were collected in a Douglas-fir (Pseudotsuga menziesii Franco) forest near Corvallis, Oregon, and maintained for 20 to 40 days in controlled-environment chambers with atmospheric CO₂ concentrations of 374 and 700 ll^-1. Nitrogenase activity, which was assayed by the acetylene reduction method, was approximately doubled in the lichen maintained in elevated CO₂. Increases in nitrogen fixation by lichens may be an important part of the integrated ecosystem response to rising CO₂.     

Effects of manganese on chlorophyll fluorescence in epiphytic cyano- and chlorolichens

Incubation with 10 mM MnCl₂ for 1 h decreased the effective quantum yield of photochemical energy conversion in photosystem 2 in the bipartite chlorolichen Hypogymnia physodes as well as in the bipartite cyanolichens Leptogium saturninum and Nephroma helveticum, but not in the tripartite lichen Lobaria pulmonaria. Among the bipartite species, Mn sensitivity increased in the order H. physodes < N. helveticum < L. saturninum. This equals the sequence heteromerous chlorolichen < heteromerous cyanolichen < homoiomerous (gelatinous) cyanolichen. MnCl₂ reduced non-photochemical quenching of chlorophyll fluorescence in the bipartite cyanolichens and in H. physodes; in the latter, however, this decrease was limited to light intensities above the adapted growth light intensity. Photochemical quenching was increased in H. physodes, but reduced in the bipartite cyanolichens. The results indicate that the bipartite cyanolichens L. saturninum and N. helveticum are even more sensitive to high Mn concentrations than the chlorolichen H. physodes, the low Mn tolerance of which has been already demonstrated. This agrees with results of field studies from western North America, where conifer bark under cyanolichens (including L. saturninum and N. helveticum) was found to contain less Mn than bark which only supported chlorolichens. The high sensitivity of the bipartite cyanolichens probably results from high sensitivity of the Nostoc photobiont. The high Mn tolerance of L. pulmonaria is probably not due to its being a tripartite lichen, but might be caused by high tolerance of the green-algal primary photobiont Dictyochloropsis, which is, however, not experimentally proven. The high Mn tolerance of the highly SO₂-sensitive L. pulmonaria shows that different mechanisms are responsible for Mn and SO₂ toxicity in lichens.     

Sterols of three lichen species: Lobaria pulmonaria, Lobaria Scrobiculata and Usnea Longissima

Sterols were extracted from the lichens Lobaria pulmonaria, Lobaria scrobiculata and Usnea longissima with chloroform-methanol (2:1) (solvent-extractable fraction) followed by saponification of the residual lichen material to give a tightly-bound sterol fraction. The compounds were principally ergosterol, episterol, fecosterol and lichesterol with minor quantities of C₁₇, C₂₈ and C₂₉ monoenes and dienes of the phytosterol type.