Competitive equivalence in a community of lichens on rock

Lichens and mosses cover 70–100% of the rock surface in a forested Appalachian boulderfield, and competition for space is intense. This paper examines overgrowth ability and its morphological correlates in four common species of foliose lichen on rocks. Overgrowth requires one lichen thallus to overtop another at the point where they meet. Therefore, I quantified margin height for a number of thalli of each of four lichen species. Two umbilicate species attached to the rock only at the thallus center showed a positive relationship between thallus size and margin height: large thalli often reached considerable heights above the rock surface, yet most also had points along their margin that were quite low and flat. Two other nonumbilicate species were characteristically flatter and showed no dependence of margin height on thallus diameter. Differences among species, among thalli of the same species, and among different points on a single thallus accounted for approximately equal amounts of variance in margin height. To determine the success of species in overtopping each other, I then recorded 639 instances of apparent overgrowth (overtopping of one thallus by another) on several rocks in the boulderfield. Of the nine pairs of species that met often enough to permit statistical analysis, only four pairs showed a consistent winner. Species in the remaining five pairs were competitively equivalent, neither winning significantly more than half the encounters although each individual encounter had a clear winner. Overgrowth rates measured from sequential photographs were highly variable, but many species pairs showed no substantial differences between growth rates over another thallus and growth rates over bare rock; only one species appeared to be affected by overgrowing other thalli. Overgrown thalli, as well as thalli experimentally shaded by gluing an overhanging rock chip above their margin for a year grew very slowly or not at all in the region of overgrowth, and the overgrown region of the thallus was often markedly discolored or disintegrating. Thus, foliose lichens compete strongly for space at the study site, yet because competitive success is at least partly based on a morphological character (margin height) that is inherently quite variable even in a single thallus, many pairs of species appear to be competitively equivalent.     

QUANTITATIVE VARIATION IN VULPINIC AND PINASTRIC ACIDS PRODUCED BY TUCKERMANNOPSIS PINASTRI (LICHEN-FORMING ASCOMYCOTINA,PARMELIACEAE)

Tuckermannopsis pinastri is a lichen species found commonly on rocks and tree branches in boreal and alpine habitats in the northern United States. Members of this species produce three yellow-pigmented phenolic compounds: usnic, pinastric, and vulpinic acids. The objective of our study was to quantify the variation in concentration of the latter two of these compounds in relation to substrate factors, chlorophyll content, and thallus size. Using high-performance liquid chromatography, we analyzed 120 thalli of T. pinastri collected randomly from a single large population located at Spruce Knob, West Virginia. Although individuals were sampled from both tree and rock substrates that differed markedly in light intensity, these environmental factors were not correlated with observed variations in vulpinic or pinastric acid concentrations. Instead, compound concentrations were correlated most closely with thallus size, with small rather than large thalli having the highest concentrations of the two compounds. Small thalli did not have higher concentrations of chlorophylls than large thalli, however, which suggests that the rate of production of secondary compounds by the fungus in T. pinastri is independent of algal biomass. Inasmuch as lichen secondary compounds serve a defensive role against microorganisms and herbivores, our results suggest that small, juvenile thalli are better defended than more mature thalli.     

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.     

DISPERSAL PATTERNS OF TERRICOLOUS LICHENS BY THALLUS FRAGMENTS

Dispersal patterns from seven terricolous lichen species, with a high capacity for asexual reproduction by fragmentation (Cetraria muricata, Cladonia species), were studied in differing vegetation types in north-eastern Germany. Marked lichen thalli were fragmented by trampling. After 15 days the spread of thallus fragments was monitored. Whereas most of the fragments that were dispersed by wind remained within a 20-cm radius from the source, the maximal dispersal distance was 57 cm in a dry sand grassland and 68 cm in an open pioneer pine forest. Dispersal was negligible in a closed old-growth pine forest. Several fragmented lichen cushions were disturbed and removed by animals, and led to a maximal dispersal distance of 9·70 m. These results suggest that: (a) thallus fragments provide good short-distance dispersal in open vegetation, but are inefficient for long-distance dispersal, and (b) wind and animals are important factors for the dispersal of thallus fragments. For restoration management of man-made substrata, artificial introduction of lichen thalli is proposed.     

Do secondary substances in the thallus of a lichen promote CO2 diffusion and prevent depression of net photosynthesis at high water content?

Many lichens show seriously depressed net photosynthesis (NP) at high thallus water contents due to increased carbon dioxide diffusion resistance through blockage of diffusion pathways by water. The soil lichen Diploschistes muscorum, however, shows no depression and NP is close to maximal even at the highest thallus water content. We investigated whether lichen substances (lecanoric and diploschistesic acids) in the cortex and medulla contributed to this ability to maintain high NP. Dry thalli were extracted with water-free acetone and, after this treatment, were found to be fully viable to the extent of continued growth after replanting in the field. No differences were found in the response of NP to thallus water content between the normal and extracted thalli, in fact the response curves were often nearly identical. Thus, in this species it seems that lichen substances did not maintain the water-free diffusion pathways and some other explanation, possibly structural, needs to be sought. Received: 5 April 1997 / Accepted: 26 April 1997     

High photobiont diversity associated with the euryoecious lichen-forming ascomycete Lecanora rupicola (Lecanoraceae, Ascomycota)

The diversity and phylogenetic position of photobionts in the widespread saxicolous, crustose lichen-forming ascomycete Lecanora rupicola s.l. is presented. The algal partners of this lichen species complex belong to diverse and unrelated lineages in the genus Trebouxia . Specimens were sampled from different habitats and geographical origins. Either whole thallus DNA extractions or minute fragments of the algal layer of the lichen thallus were subjected to polymerase chain reaction, using primers that specifically amplify internal transcribed spacer rDNA of the photobionts. No correlations between different chemical races of L. rupicola with particular lineages of Trebouxia spp. were found. Irrespective of the different algal partners, all lichen thalli abundantly developed ascomata. L. rupicola apparently maintains full fecundity with a low degree of selectivity for photobionts, which promotes the occurrence of this lichen-forming species in ample ecological situations.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 283–293.     

Heterogeneity of Chlorophyll Fluorescence over Thalli of Several Foliose Macrolichens Exposed to Adverse Environmental Factors: Interspecific Differences as Related to Thallus Hydration and High Irradiance

Spatial heterogeneity of chlorophyll (Chl) fluorescence over thalli of three foliose lichen species was studied using Chl fluorescence imaging (CFI) and slow Chl fluorescence kinetics supplemented with quenching analysis. CFI values indicated species-specific differences in location of the most physiologically active zones within fully hydrated thalli: marginal thallus parts (Hypogymnia physodes), central part and close-to-umbilicus spots (Lasallia pustulata), and irregulary-distributed zones within thallus (Umbilicaria hirsuta). During gradual desiccation of lichen thalli, decrease in Chl fluorescence parameters (F_O - minimum Chl fluorescence at point O, F_P - maximum Chl fluorescence at P point, ₂ - effective quantum yield of photochemical energy conversion in photosystem 2) was observed. Under severe desiccation (>85 % of water saturation deficit), substantial thalli parts lost their apparent physiological activity and the resting parts exhibited only a small Chl fluorescence. Distribution of these active patches was identical with the most active areas found under full hydration. Thus spatial heterogeneity of Chl fluorescence in foliose lichens may reflect location of growth zones (pseudomeristems) within thalli and adjacent newly produced biomass. When exposed to high irradiance, fully-hydrated thalli of L. pustulata and U. hirsuta showed either an increase or no change in F_O, and a decrease in F_P. Distribution of Chl fluorescence after the high irradiance treatment, however, remained the same as before the treatment. After 60 min of recovery in the dark, F_O and F_P did not recover to initial values, which may indicate that the lichen used underwent a photoinhibition. The CFI method is an effective tool in assessing spatial heterogeneity of physiological activity over lichen thalli exposed to a variety of environmental factors. It may be also used to select a representative area at a lichen thallus before application of single-spot fluorometric techniques in lichens.     

Intrathalline and size-dependent patterns of activity in Lasallia pustulata and their possible consequences for competitive interactions

1. In dense populations of the saxicolous lichen Lasallia pustulata the margins of adjacent thalli overlap each other in intraspecific competition for space and light.
2. In situ non-destructive monitoring of hydration-dependent potential photosynthetic activity by modulated fluorescence systems in different parts of the thallus shows that the activity is structured by a centre-to-margin gradient, with the centre of the thallus remaining active for substantially longer periods than the margins when the thalli dry up after being activated by wetting. The pattern reflects the water status of different parts of the thallus; the margins which are thin and exposed dry up first.
3. The activity pattern within individual lichen thalli suggests that marginal overlapping between neighbours may have a less detrimental effect on the shadowed individuals than expected from a pure consideration of the amount of area shadowed. Because the centre of the lichen thallus is active for longer periods, shadowing of this region may possibly be more harmful per area unit than an overlap at the less active margins.
4. Larger thalli are active for substantially longer periods than small ones. Even the margins of larger thalli tend to be active for a longer period than the centre of small thalli.     

Growth of foliose lichens: a review

This review considers various aspects of the growth of foliose lichens including early growth and development, variation in radial growth rate (RaGR) of different species, growth to maturity, lobe growth variation, senescence and fragmentation, growth models, the influence of environmental variables, and the maintenance of thallus symmetry. The data suggest that a foliose lichen thallus is essentially a ‘colony’ in which the individual lobes exhibit a considerable degree of autonomy in their growth processes. During development, recognisable juvenile thalli are usually formed by 15 months to 4 years while most mature thalli exhibit RaGR between 1 and 5 mm yr⁻¹. RaGR within a species is highly variable. The growth rate-size curve of a foliose lichen thallus may result from growth processes that take place at the tips of individual lobes together with size-related changes in the intensity of competition for space between the marginal lobes. Radial growth and growth in mass is influenced by climatic and microclimatic factors and also by substratum factors such as rock and bark texture, chemistry, and nutrient enrichment. Possible future research topics include: (1) measuring fast growing foliose species through life, (2) the three dimensional changes that occur during lobe growth, (3) the cellular changes that occur during regeneration, growth, and division of lobes, and (4) the distribution and allocation of the major lichen carbohydrates within lobes.     

Ultrastructure of snail grazing damage to calcicolous lichens

The identification of damaged lichens is often difficult due to changes in the morphology of regenerating specimens. We examined the Ultrastructure of grazing damages to four species of calcicolous lichens ( Aspicilia calcarea, Physcia adscendens, Tephromela atra and Xanthoria parietina ) and free-living cyanobacteria (family Chroococcaceae) caused by individuals of four species of land snails ( Chondrina clienta, Balea perversa, Clausilia bidentata and Helicigona lapicida ). We also investigated the radular structure of the four lichen-feeding snails to examine whether differences in radular morphology result in species-specific grazing damages. Individuals of all four snail species removed the cyanobacteria layer covering the limestone or lichen surfaces. The four lichen species were grazed to a different extent by the different snail species. SEM-images showed that B. perversa left distinct depressions on the thalli of A. calcarea , whereas H. lapicida grazed off the thalli of this lichen rather evenly. Both snail species left visible radular traces on the lichen surface. In contrast, Ch. clienta left shallow depressions without radular traces on the thalli of A. calcarea. In Tephromela atra , grazing damages were observed on both thallus and ascocarp. Ascocarps of T. atra were partly grazed by B. perversa. Helicigona lapicida grazing on T. atra removed more or less evenly the entire lichen tissue including the ascocarps. In foliose lichens, grazing by Ch. clienta, B. perversa and Cl. bidentata resulted in depressions of different depths, while H. lapicida removed entire pieces of the thalli. In general, radular traces were less distinct in foliose lichens than in crustose lichens.     

Water Distribution in Foliose Lichen Species: Interactions between Method of Hydration, Lichen Substances and Thallus Anatomy

Three lichens (Neofuscelia pokornyi, N. pulla and Xanthoriaparietina) from a semi-arid habitat were examined using low-temperaturescanning electron microscopy to evaluate the effects of hydrationmethod, lichen substances and thallus anatomy on the water distributionof hydrated thalli. In theNeofuscelia species, extracellularwater within the thallus was observed in association with cracksin its otherwise impervious upper cortex, while X. parietinashowed abundant extracellular water between medullary hyphae.Spraying the thalli followed by maintenance for 14–20h in a water-saturated atmosphere led to the disappearance ofthe external water film in X. parietina but not in the Neofusceliaspecies. Surface water was abundant in specimens of all speciesimmediately after spraying for 15 min. No extracellular waterwas observed inside the thallus 14–20 h after spraying,but after rinsing with acetone its presence was detected inall three species. Hydric strategy correlated with cortex hygroscopicity:X. parietina, an aero-hygrophytic species, had a more hygroscopicupper cortex than theNeofuscelia species, which are substrate-hygrophytic.The hygroscopicity of the upper cortex was linked with the amountof extracellular water in the thalline interior. Differencesbetween X. parietina and Neofuscelia in the polarity and distributionof their lichen substances agreed with species differences inthe presence and distribution of free water both as a film overthe surface and inside the thallus. Lichen substances appearto play a role in the maintenance of air-filled intrathallinespaces in species whose anatomy, habitat, or both, favour water-loggedconditions. Copyright 2000 Annals of Botany Company Lichen, water relations, semi-arid, lichen substances, LTSEM, thallus anatomy, extracellular water, Neofuscelia pokornyi(Körb.) Essl., Neofuscelia pulla(Ach.) Essl., Xanthoria parietina(L.) Th. Fr     

Symbiosis as a successful strategy in continental Antarctica: performance and protection of Trebouxia photosystem II in relation to lichen pigmentation

Lichens as symbiotic associations consisting of a fungus (the mycobiont) and a photosynthetic partner (the photobiont) dominate the terrestrial vegetation of continental Antarctica. The photobiont provides carbon nutrition for the fungus. Therefore, performance and protection of photosystem II is a key factor of lichen survival. Potentials and limitations of photobiont physiology require intense investigation to extend the knowledge on adaptation mechanisms in the lichen symbiosis and to clarify to which extent photobionts benefit from symbiosis. Isolated photobionts and entire lichen thalli have been examined. The contribution of the photobiont concerning adaptation mechanisms to the light regime and temperature conditions was examined by chlorophyll a fluorescence and pigment analysis focusing on the foliose lichen Umbilicaria decussata from North Victoria Land, continental Antarctica. No photoinhibition has been observed in the entire lichen thallus. In the isolated photobionts, photoinhibition was clearly temperature dependent. For the first time, melanin in U. decussata thalli has been proved. Though the isolated photobiont is capable of excess light protection, the results clearly show that photoprotection is significantly increased in the symbiotic state. The closely related photobiont of Pleopsidium chlorophanum, a lichen lacking melanin, showed a higher potential of carotenoid-based excess light tolerance. This fact discriminates the two photobionts of the same Trebouxia clade. Based on the results, it can be concluded that the successful adaptation of lichens to continental Antarctic conditions is in part based on the physiological potential of the photobionts. The findings provide information on the success of symbiotic life in extreme environments.     

POROSIMETRIC STUDY OF THE LICHEN FAMILY UMBILICARIACEAE: ANATOMICAL INTERPRETATION AND IMPLICATIONS FOR WATER STORAGE CAPACITY OF THE THALLUS

The pore system within the thalli of 13 lichen taxa belonging to the family Umbilicariaceae has been studied by means of mercury intrusion porosimetry. A characteristic bimodal pore size distribution with a central depression around 0.05 μm of equivalent pore radius was obtained in all lichen samples. However, clear differences were found among the pore size distributions of each lichen taxa. The total thallus porosity was undoubtedly related to the anatomy of the medulla. In general, a radial plectenchymatic medulla conferred larger porosity to the thallus than an arachnoidal one. Maximum thallus water content closely depended on the total thallus porosity in the five lichens possessing rhizinomorphs. The species with a similar type of medulla could be grouped together in a multivariate analysis that considered three porosimetric parameters and the maximum thallus water content. Umbilicaria cinereorufescens was the most distinct species, with the lowest values of total porosity and water storage capacity and the largest value of thallus density, apparently due to its scleroplectenchymatic medulla. The pore size distribution existing inside the thallus of the species studied is discussed in relation to the often opposing problems of CO₂ exchange and optimal water relations. Some results pointed to a large influence of the micropores (<0.05 μm) on the water storage capacity of the thallus, while the macropores would have a more important role in gas exchange.     

不同水分条件下两种叶状地衣的光合活性对冻融交替的响应

冻融交替是我国北方常见气候现象,其对地衣光合作用的影响尚不清楚。研究了采自雾灵山的卷叶点黄梅Flavopunctelia soredica和平盘软地卷Peltigera elisabethae的光合活性(以净光合速率表示,net photosynthetic rate,Pn)对冻融处理的响应及其与地衣体含水量(干冻组:含水量<20%干重;湿冻组:含水量>200%)和物种的关系。结果显示卷叶点黄梅的干冻组Pn经5次冻融后下降至对照的21%,湿冻组经3次冻融后下降至负值,平盘软地卷的干冻组和湿冻组在5次冻融后Pn均为负值;相对净光合速率(relative net photosynthetic rate,Rpn)与冻融次数的线性回归分析表明,卷叶点黄梅湿冻组的斜率绝对值(58.06)>平盘软地卷湿冻组(41.01)>平盘软地卷干冻组(32.27)>卷叶点黄梅干冻组(11.44)。结果表明冻融胁迫可显著抑制两种地衣的光合活性,这种抑制作用具有物种差异且和地衣体内水分含量有关:水分含量的增高将增强冻融胁迫对地衣光合活性的抑制作用;干燥状态下,卷叶点黄梅的低温耐性远高于平盘软地卷,但在湿润状态下则低于后者。两种地衣对冻融循环的光合响应的物种差异与其微生境气候有关:生长于较干燥开阔地带的卷叶点黄梅与生于阴湿生境中的平盘软地卷相比,可能已形成了更强的低温干燥适应能力,其低温湿润适应能力则较弱。全球气候变化可能会通过冻融事件的时空格局的改变而对地衣的光合作用和分布造成负面影响。     

Further evidence that activation of net photosynthesis by dry cyanobacterial lichens requires liquid water

Abstract: In contrast to green algal lichens, cyanobacterial species of different families, growth forms and habitats proved to be unable to attain positive net CO₂ assimilation when the dry thalli were treated with air of high relative humidity; they needed liquid water for the reactivation of their photosynthetic apparatus. Identical behaviour is shown by all of the 47 lichen species with cyanobacterial photobionts, from six different genera, studied so far. This suggests a widely distributed, if not general, characteristic of cyanobacterial lichens. The difference in performance between both groups of photobionts was maintained when the lichen thallus was macerated. Furthermore, cultures of Chroococcidiopsis were unable to make use of water vapour hydration for positive net photosynthesis, and were similar in this respect to some free-living aerophilic cyanohacteria tested earlier. Possible physiological implications as well as ecological consequences for water-relation-dependent habitat selection of green-algal and cyanobacterial lichens are discussed.     

Biomonitoring of indicator species of lichen by EPR spectroscopy

EPR spectroscopy is beginning to occupy a key position in the field of quality control environment. The analysis of the number of paramagnetic centers in the thallus of indicator species of lichen (in a tolerant and sensitive species) was carried out. The number of paramagnetic centers in the lichen thallus was found to depend on the intensity of human impact on habitats of the species studied and their taxonomic affiliation. Possible mechanisms of resistance to atmospheric pollution for tolerant species of lichens were discussed.     

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.     

The Localization of Lead in the Lichen Ramalina duriaei (De Not.) Bagl.

In an attempt to ascertain whether the lichen Ramalina duriaei could be employed to biomonitor atmospheric lead pollution, specimens of this lichen were exposed to Pb (NO₃)₂ solutions and a buffered solution (tartaric acid/sodium bitartrate, pH 2.8) of sodium rhodizonate (C₆O₆Na₂) was used to locate lead in their thalli. The procedure entailed exposure of the lichen to 0, 5, 50 and 100 ppm Pb for 5 min and 1 h and the subsequent determination of the lead contents from photographs of the thalli. Distribution of lead in different parts of the thallus was assessed after exposure of the lichens to 2 ppm Pb (9 h or three d), 50 ppm (45 min) or 200 ppm (4d). Cross sections of vegetative parts of the thallus and of the apothecia revealed that lead penetrated into the cortical cells of the thallus but not into the algal cells of the phycobiont nor the ascospores or medullary cells. The observed massive penetration of lead into cortical cells supports the notion that Ramalina duriaei is sensitive to atmospheric lead pollution.     

Moisture content and CO2 exchange of lichens

Summary Net photosynthesis (10 klx light intensity, 150 E m^-2 s^-1 PAR) and dark respiration of the lichen Ramalina maciformis at different temperatures are measured in relation to thallus water content. Both first increase with increasing hydration. Dark respiration then remains constant with increased water content until thallus saturation. In contrast, a further increase in water content leads to a depression of net photosynthesis, as shown in previous studies, after a maximum of CO₂ uptake has been attained. However, the extent of this depression depends strongly on temperature. In saturated thalli (160% water content in relation to lichen dry weight) the depression amounts to about 15% and 63% of the maximum unsaturated rate at 5°C and 25°C thallus temperature, respectively. The moisture compensation-point of net photosynthesis is also decisively determined by temperature (for 0°C at 20% water content; for 25°C at 15%), and the water content that allows maximum rates of CO₂ uptake (for 0°C at 80%; for 25°C at less than 40% water content). An electrical analogue of CO₂ exchange in a lichen thallus is presented, and it is suggested that the experimental results may be interpreted in terms of temperature-dependent CO₂ diffusion resistances in imbibed lichen thalli.     

Thallus growth asymmetry and habitat inclination in Lasallia pustulata

The relationship between thallus shape and habitat inclination in the umbilicate lichen Lasallia pustulata is investigated. There is a significant relationship between the steepness of the habitat rock surface and the degree of asymmetry around the central holdfast of the thalli. This is interpreted as an effect of gravity, including the gravity-influenced over-under 'tiling' of the lichens on the habitat surface. There was no correlation between thallus size and degree of asymmetry.