Carbon-dioxide exchange in lichens: determination of transport and carboxylation characteristics

Measurements were made of net rates of CO₂ assimilation in lichens at various ambient concentrations of CO₂ in air and in helox (79% He, 21% O₂). Because of the faster rate of CO₂ diffusion in the pores of lichen thalli when filled with helox than when filled with air, a given net rate of assimilation was achieved at a lower ambient concentration of CO₂ in helox. The differences were used to estimate resistances to diffusion through the gas-filled pore systems in lichens. The technique was first tested with five lichen species, and then applied in a detailed study with Ramalina maciformis, in which gas-phase resistances were determined in samples at four different states of hydration and with two irradiances. By assuming, on the basis of previous evidence, that the phycobiont in R. maciformis is fully turgid and photosynthetically competent at the smallest hydration imposed (equilibration with vapour at 97% relative humidity), and that, with this state of hydration, diffusion of CO₂ to the phycobiont takes place through continuously gas-filled pores, it was possible also to determine both the dependence of net rate of assimilation in the phycobiont on local concentration of CO₂ in the algal layer, and, with the wetter samples, the extents to which diffusion of CO₂ to the phycobiont was impeded by water films. In equilibrium with air of 97% relative humidity, the thallus water content being 0.5 g per g dry weight, the resistance to CO₂ diffusion through the thallus was about twice as large as the resistance to CO₂ uptake within the phycobiont. Total resistance to diffusion increased rapidly with increase in hydration. At a water content of 2 g per g it was about 50 times as great as the resistance to uptake within the phycobiont and more than two-thirds of it was attributable to impedance of transfer by water. The influences of water content on rate of assimilation at various irradiances are discussed. The analysis shows that the local CO₂ compensation concentration of the phycobiont in R. maciformis is close to zero, indicating that photorespiratory release of CO₂ does not take place in the alga, Trebouxia sp., under the conditions of these experiments.Symbols and Units rate of CO₂ diffusion in air relative to that in carrier gas (unity if the carrier gas is air and 0.43 if is helox) - A₁ net rate of CO₂ uptake by the lichen - A_p gross rate of carboxylation minus photorespiratory decarboxylation in the phycobiont, i.e. net rate of light-activated CO₂ exchange - A_* maximum, CO₂-saturated magnitude of A_p - c concentration of CO₂ - c_a ambient concentration of CO₂ - c_i c_a minus difference in CO₂ concentration across air-filled pore space in the thallus - c₈ CO₂ concentration equivalent to partial pressure of CO₂ at the surface of the phycobiont - ₁ magnitude of c_a at which A₁ = 0 - _* magnitude of c_* at which A_p = 0 - R rate of dark respiration in the lichen (mycobiont and phycobiont) - R rate of dark respiration in region between the surface of the lichen and an arbitrary distance from the surface within the thallus - r resistance to CO₂ transfer from lichen surface to the surface of the phycobiont - r resistance to CO₂ transfer between effective source of dark respiration in the lichen and the surface of the phycobiont - r_g, r _g components of r and r, respectively, attributable to transfer in air-phase - r_w, r _w components of r and r, respectively, attributable to transfer in water-phase - r component of r between surface of lichen and an arbitrary distance from the surface within the thallus - r_* resistance to CO₂ transfer and carboxylation in the phycobiont - RH relative humidity     

Organic and inorganic nitrogen uptake in lichens

In order to learn more about nitrogen (N) acquisition in lichens, and to see whether different lichens differ in their affinity to various N sources, N uptake was measured in 14 various lichen associations (species). These species represented various morphologies (fruticose or foliose), contrasting microhabitat preferences (epiphytic or terricolous), and had green algal, cyanobacterial or both forms of photobionts. N was supplied under non-limiting conditions as an amino acid mixture, ammonium, or nitrate, using ¹⁵N to quantify uptake. Carbonyl cyanide m-chlorophenylhydrazone (CCCP) was used to separate active and passive uptake. Thallus N, amino acids, soluble polyol concentrations, and the biont-specific markers chlorophyll a and ergosterol were quantified, aiming to test if these metabolites or markers were correlated with N uptake capacity. Ammonium uptake was significantly greater and to a higher extent passive, relative to the other two N sources. Nitrate uptake differed among lichen photobiont groups, cyanobacterial lichens having a lower uptake rate. All lichens had the capacity to assimilate amino acids, in many species at rates equal to nitrate uptake or even higher, suggesting that organic N compounds could potentially have an important role in the N nutrition of these organisms. There were no clear correlations between N uptake rates and any of the measured metabolites or markers. The relative uptake rates of ammonium, nitrate and amino acids were not related to morphology or microhabitat.Abbreviations CCCP Carbonyl cyanide m-chlorophenylhydrazone - Chl Chlorophyll - N Nitrogen     

Pseudocyphellaria crocata, P. neglecta and P. perpetua from the Northern and Southern Hemispheres are a phylogenetic species and share cyanobionts

Pseudocyphellaria crocata, P. neglecta and P. perpetua specimens were examined to investigate links between genetic variation and morphology, geographical distribution and cyanobiont specificity. Fungal internal transcribed spacer (ITS), beta-tubulin and cyanobacterial tRNA(Leu) (UAA) intron sequences were used to investigate symbiont diversity in these lichens. Specimens were morphologically distinct but could not be distinguished by ITS sequences. Phylogenetic analyses split the P. crocata specimens into two clades, the larger of which contained P. neglecta and P. perpetua. Five cyanobionts were identified; two of these were in a number of specimens, while three were each restricted to a single lichen thallus. Fungus-specific molecular markers indicated that all specimens belonged to a single phylogenetic species. However, this may contain a cryptic species. Geography was linked to genetic diversity with Canadian specimens forming a monophyletic group, and most Southern Hemisphere specimens grouping together, although Chile represented a hot spot of genetic diversity. There was no connection between fungal genetic diversity and cyanobiont choice, consistent with the presence of a common pool of cyanobionts.     

Cyanobiont specificity in some Nostoc-containing lichens and in a Peltigera aphthosa photosymbiodeme

The cyanobacterial symbionts in some Nostoc -containing lichens were investigated using the nucleotide sequence of the highly variable cyanobacterial tRNA^Leu (UAA) intron. When comparing different Nostoc -containing lichens, identical intron sequences were found in different samples of the same lichen species collected from two remote areas. This was true for all species where this comparison was made ( Peltigera aphthosa (L.) Willd., P. canina (L.) Willd. and Nephroma arcticum (L.) Torss.). With one exception, a specific intron sequence was never found in more than one lichen species. However, for two of the species, Peltigera aphthosa and Nephroma arcticum , two different cyanobionts were found in different samples. By examining a P. aphthosa photosymbiodeme it could be shown that the same Nostoc is present in both bipartite and tripartite lobes of this lichen. It is thus possible for one cyanobiont/ Nostoc to form the physiologically different symbioses that are found in bipartite and tripartite lichens. The connection between photobiont identity and secondary chemistry is discussed, as a correlation between differences in secondary chemistry and different cyanobionts/ Nostoc s in the species Peltigera neopolydactyla (Gyeln.) Gyeln. was observed. It is concluded that more knowledge concerning the photobiont will give us valuable information on many aspects of lichen biology.     

新疆地衣研究现状与展望

地衣在自然界中是一种特殊的生物类群,具有独特的结构特征和较强的环境适应能力。它在环境污染评价,药物和香料开发利用方面具有较高的研究价值。目前对地衣的研究涉及地衣分类、地衣区系地理、地衣群落生态学、地衣化学、利用地衣评价环境质量以及地衣分子生物学等领域。回顾了新疆地衣研究近20年的发展概况,总结了新疆地衣研究的发展历程、特点,并展望了新疆地衣研究的方向。     

Photosynthetic CO2-use efficiency in lichens and their isolated photobionts: the possible role of a CO2-concentrating mechanism

The CO₂ dependence of net CO₂ assimilation was examined in a number of green algal and cyanobacterial lichens with the aim of screening for the algal/cyanobacterial CO₂-concentrating mechanism (CCM) in these symbiotic organisms. For the lichens Peltigera aphthosa (L.) Willd., P. canina (L.) Willd. and P. neopolydactyla (Gyeln.) Gyeln., the photosynthetic performance was also compared between intact thalli and their respective photobionts, the green alga Coccomyxa PA, isolated from Peltigera aphthosa and the cyanobacterium Nostoc PC, isolated from Peltigera canina. More direct evidence for the operation of a CCM was obtained by monitoring the effects of the carbonic-anhydrase inhibitors acetazolamide and ethoxyzolamide on the photosynthetic CO₂use efficiency of the photobionts. The results strongly indicate the operation of a CCM in all cyanobacterial lichens investigated and in cultured cells of Nostoc PC, similar to that described for free-living species of cyanobacteria. The green algal lichens were divided into two groups, one with a low and the other with a higher CO₂-use efficiency, indicative of the absence of a CCM in the former. The absence of a CCM in the low-affinity lichens was related to the photobiont, because free-living cells of Coccomyxa PA also apparently lacked a CCM. As a result of the postulated CCM, cyanobacterial Peltigera lichens have higher rates of net photosynthesis at normal CO₂ compared with Peltigera aphthosa. It is proposed that this increased photosynthetic capacity may result in a higher production potential, provided that photosynthesis is limited by CO₂ under natural conditions.     

Caractérisation de la sticticine chez le lichen Lobaria laetevirens

Sticticin has been isolated from the thallus of Lobaria laetevirens. Its structure was determined by spectroscopic methods (NMR, MS) and comparison with a synthetic sample. It has been found in several species of the Stictaceae.     

地衣标本的采集、制作与保存

详细论述了地衣标本的采集、制作和保存方法及注意事项,同时阐明了在采集标本的同时进行共生菌和光合共生物分离培养的重要性。     

头发七多糖的化学研究

头发七经有机溶媒脱色、热水提取、乙醇沉淀及进一步精制得头发七多糖（ＡＬＪ）。该多糖经Ｓｅｐｈａｄｅｘ Ｇ－７５柱层析证明为均一多糖,气相色谱测得头发七多糖是由鼠李糖（Ｒｈａ）、阿拉伯糖（Ａｒａ）、木糖（Ｘｙｌ）、甘露糖（Ｍａｎ）、葡萄糖（Ｇａｌ）聚合而成的杂多糖,其摩尔比为３．４３：２．８６：１．００：８．５７：８５．７１：５．７１。经Ｓｅｐｈａｄｘ Ｇ－２００凝胶过滤法测得其平均分子量为１．８５     

Responses of the green algal foliose lichen Platismatia glauca to increased nitrogen supply

Nitrogen (N) availability and light exposure were manipulated under field conditions to study responses to altered resource supply in the green algal lichen Platismatia glauca. The lichen was fertilized with different concentrations and frequencies of ammonium, nitrate or glutamine under different light regimes for 2-3 months. Responses were followed from the intact thallus to the cellular level. Despite significant differences in overall light exposure, light conditions were not significantly different among treatments when the lichens were wet and active. Ammonium was the preferred N source, followed by glutamine and then nitrate. Thallus N concentration as well as the chlorophyll a (Chl a) concentration increased 3-4-fold at the highest ammonium concentration, while the mycobiont ergosterol concentration remained unaltered. Growth was significantly enhanced by the enhanced N supply, with the increase in dry weight varying from 3 to 30%. Variation in Chl a concentration explained 31% of this variation, suggesting a causal link to the increased growth rate. Platismatia glauca responded to increased N availability by increasing its growth rate and carbon assimilation capacity through increased investments in the photobiont cells. This suggests a tight regulation of resource investments and metabolic pathways between the symbionts of this lichen.     

Meristem growth dynamics and branching patterns in the Cladoniaceae

Branching patterns in the lichen family Cladoniaceae are varied and taxonomically important. Branching occurs on the podetium, the erect secondary thallus that characterizes most species in the Cladoniaceae, and is influenced by growth dynamics of the fungal meristem tissue at the apex of the podetium. Branching is primarily the result of meristem divisions, and branching patterns are modified by meristem enlargement, deformation, and torsion. Branching processes are conserved, and early branch ontogeny provides information from which to determine relationships in the Cladoniaceae. Branching is characterized by two major patterns. In one pattern, branches arise from the relatively late divisions of a large meristem (≥100 μm in diameter), whose shape changes during ontogeny. In a second pattern, branches arise from small meristems (<100 μm in diameter), which split early in ontogeny but whose shape does not change. The trend toward reduced meristems that split early in ontogeny is seen as an evolutionary advance in the Cladoniaceae. Some "small meristem" species retain aspects of the "large meristem" habit in early ontogeny, and this provides a clue to their relationships. Patterns of meristem growth dynamics provide a basis for interpreting phylogeny in mycobionts of the Cladoniaceae. Meristem activities in four genera of the Cladoniaceae were compared in order to determine trends in growth dynamics within the family.     

宁夏贺兰山东麓荒漠草原区地衣的物种多样性研究

地衣是宁夏贺兰山东麓荒漠草原区一类重要的生物资源,地衣结皮的形成为该区域景观的稳定作出了重要的贡献。该研究于2014~2019年在贺兰山东麓荒漠草原区开展了地衣的野外调查,利用表型特征和DNA序列分析且对采集的500余份标本进行了物种的鉴定,并分析了其物种组成及地理成分。结果显示：(1)共鉴定地衣19科41属74种,其中中国新记录25种,新种2个(待发表),新记录属11个,宁夏新记录56种。(2)研究区地衣物种区系地理成分以北温带成分为主(33.78%),其他主要区系成分包括欧亚成分和世界广布成分等,具有明显的北温带成分区系特征。(3)研究区地衣以壳状和鳞状地衣为主(81.1%),生长型体现了地衣对当地气候条件的适应特性。实地调查发现宁夏贺兰山东麓荒漠草原区地衣的生存环境非常脆弱。该研究结果有助于提高对该区域地衣物种多样性的认识并促进其保护。     

Photobiont-related differences in carbon acquisition among green-algal lichens

The photosynthetic properties of a range of lichens (eight species) containing green algal primary photobionts of either the genus Coccomyxa, Dictyochloropsis or Trebouxia were examined with the aim of obtaining a better understanding for the different CO₂ acquisition strategies of lichenized green algae. Fast transients of light/dark-dependent CO₂ uptake and release were measured in order to screen for the presence or absence of a photosynthetic CO₂-concentrating mechanism (CCM) within the photobiont. It was found that lichens with Trebouxia photobionts (four species) were able to accumulate a small pool of inorganic carbon (DIC; 70–140 nmol per mg chlorophyll (Chl)), in the light, which theoretically may result in, at least, a two to threefold increase in the stromal CO₂ concentration, as compared to that in equilibrium with ambient air. The other lichens (four species), which were tripartite associations between a fungus, a cyanobacterium (Nostoc) and a green alga (Coccomyxa or Dictyochloropsis) accumulated a much smaller pool of DIC (10–30 nmol·(mg Chl)^–1). This pool is most probably associated with the previously documented CCM of Nostoc, inferred from the finding that free-living cells of Coccomyxa did not show any signs of DIC accumulation. In addition, the kinetics of fast CO₂ exchange for free-living Nostoc were similar to those of intact tripartite lichens, especially in their responses to the CCM and the carbonic anhydrase (CA) inhibitor ethoxyzolamide. Trebouxia lichens had a higher photosynthetic capacity at low and limiting external CO₂ concentrations, with an initial slope of the CO₂-response curve of 2.6–3.9 mol·(mg Chl)^–1·h^–1·Pa^–1, compared to the tripartite lichens which had an initial slope of 0.5–1.1 mol-(mg Chl)^–1·h^–1·-Pa^–1, suggesting that the presence of a CCM in the photobiont affects the photosynthetic performance of the whole lichen. Regardless of these indications for the presence or absence of a CCM, ethoxyzolamide inhibited the steady-state rate of photosynthesis at low CO₂ in all lichens, indicating a role of CA in the photosynthetic process within all of the photobionts. Measurements of CA activity in photobiont-enriched homogenates of the lichens showed that Coccomyxa had by far the highest activity, while the other photobionts displayed only traces or no activity at all. As the CCM is apparently absent in Coccomyxa, it is speculated that this alga compensates for this absence with high internal CA activity, which may function to reduce the CO₂-diffusion resistance through the cell.Abbreviations CA carbonic anhydrase (EC 4.2.1.1) - CCM CO₂-concentrating mechanism - Chl chlorophyll - DIC dissolved inorganic carbon - EZ ethoxyzolamide or 6-ethoxy-2-benzo-thiazole-2-sulfonamide - GA glycolaldehyde - Hepps 4-(2-hydroxyethyl)-l-piperazinepropanesulfonic acid - Rubisco ribulose-1,5-bisphosphate carboxylase-oxygenase (EC 4.1.1.39) This research was supported by a grant from the Swedish Natural Sciences Resource Council to K.P.     

荒漠化地区生物结皮的研究进展

防沙、治沙和固沙一直以来是荒漠化生态环境建设的热点问题。作者从生物结皮对荒漠化地区生态环境的影响,以及在生态系统演替中起到的重要作用等方面进行了综述,指出了地衣在生物结皮中所占有的重要地位,展望了生物结皮研究与应用的前景。     

中国癞屑衣属新记录种

首次报道了中国产癞屑衣属(Lepraria)地衣新记录3种,即Lepraria lobificans Nyl.、L.eburnea J.R.Laundon和L.caesioalba(B.de Lesd.)J.R.Laundon。文中对它们的生境、识别特征、地理分布作了简要概述。