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In Italy, many lichen species rare at the national level share their ecological requirements with Lobaria pulmonaria. The aim of this work is to test this lichen as a potential indicator for assessing forest sites which are worthy of conservation for lichens in Italy. The hypothesis to be tested is that stands hosting large and viable populations of this lichen also host nationally rare and sensitive lichen species. The study was carried out in two large forested areas of Italy under different bioclimatic conditions and with different forest types: Cansiglio Forest, in NE Italy, and Cilento in SW Italy. Three types of stands characterized by different abundance levels of L. pulmonaria were identified in each site. Ten plots for each type of stand were surveyed in each site. Macrolichens were surveyed on a total of 180 trees. The abundance of L. pulmonaria proved to be a valuable indicator of forest stands hosting nationally rare lichen species and cyanolichens in different forest types and in different bioclimatic conditions. Significant differences in species richness, in the occurrence and abundance of nationally rare lichen species and cyanolichens, and in species composition were found in both sites among stands with different levels of L. pulmonaria. Results are expected to contribute to the development of more lichen-oriented criteria in nature protection policies. © 2009 Elsevier Ltd. All rights reserved.

In the last two centuries, native European oak forests have undergone a dramatic decline related to increasing human pressure for agriculture and urbanization. Oak forests were either completely eradicated and transformed into agricultural landscapes or replaced by second-growth formations. Intensive forest management and the replacement of native forests with production forests or arable lands are recognized amongst the main threats to many lichens in Europe. In this study, we used historical information on the epiphytic lichen biota which was hosted in a native oak-dominated forest of Northern Italy to identify shifts of lichen communities due to the changes in land use which occurred during the last two centuries. We also compared the epiphytic lichen communities inhabiting remnant oak forests with those found in the habitats that have replaced native forests: black-locust forests and agrarian landscapes. Almost all the species sampled during the 19th century are now extinct. The loss of native habitat and the subsequent invasion by black locust were probably the most influential factors which affected the composition of lichen communities, causing the local extinction of most of the species historically recorded. Despite the fact that oak remnants host only a few species which were historically recorded, and that they currently are the lichen poorest habitat in the study region, they host lichen assemblages differing from those of black-locust forests and agrarian stands. In these habitats lichen assemblages are mainly composed of species adapted to well-lit, dry conditions and tolerating air pollution and eutrophication. This pattern is likely to be common also in other lowland and hilly regions throughout Northern Italy where oak forests are targeted among the habitats of conservation concern at the European level. For this reason, a national strategy for biodiversity conservation and monitoring of lowlands forests should provide the framework for local restoration projects. © 2010 Elsevier B.V.

We show that the cyanobacterial symbionts of a tripartite cyanolichen can produce hepatotoxic microcystins in situ. Microcystins were detected with high-performance liquid chromatography mass spectrometry both from cephalodia of the tripartite cyanolichen Peltigera leucophlebia and from a symbiotic Nostoc strain isolated from the same lichen specimen. Genetic identities of symbiotic Nostoc strains were studied by amplifying and sequencing the 16S rRNA gene. Also, the presence of the microcystin synthetase gene mcyE was confirmed by sequencing. Three highly toxic microcystins were detected from the lichen specimen. Several different Nostoc 16S rRNA haplotypes were present in the lichen sample but only one was found in the toxin-producing cultures. In culture, the toxin-producing Nostoc strain produced a total of 19 different microcystin variants. In phylogenetic analysis, this cyanobacterium and related strains from the lichen thallus grouped together with a previously known microcystin-producing Nostoc strain and other strains previously isolated from the symbiotic thalloid bryophyte Blasia pusilla. Our finding is the first direct evidence of in situ production of microcystins in lichens or plant–cyanobacterial symbioses. Microcystins may explain why cyanolichens and symbiotic bryophytes are not among the preferred food sources of most animal grazers.

Two lichen species (Peltigera rufescens and Cladina arbuscula subsp. mitis) and one moss species (Racomitrium lanuginosum) growing on a copper mine heaps (probably 200-300yr old) in the village of Spania dolina (Slovak Republic) were assessed for selected physiological parameters, including composition of assimilation pigments, chlorophyll a fluorescence, soluble proteins and free amino acid content. The lichen C. arbuscula subsp. mitis was collected also at a control locality where total copper concentration in the soil was approximately 3% that of the waste heaps. Concentrations of Al, Co, Cu, Ni, Sb and Zn were highest in thalli of Peltigera, while the moss Racomitrium contained the highest content of Fe and Pb. Thalli of Cladina contained less metals than the cyanolichen Peltigera, and except for Zn metal concentrations in Cladina from the control locality were lower than in thalli of the same species from copper mine heaps. Regardless of the species or locality, the composition of assimilation pigments and chlorophyll a fluorescence showed that the tested lichens and moss were in good physiological condition and adapted to increased copper levels in the soil. There were significantly different amounts of total free amino acids in Peltigera, Cladina and Racomitrium from the Cu-polluted field. However, differences in amount of free amino acids in control, as well as Cu-polluted thalli of Cladina were less pronounced.

Lichens are reputedly slow growing and become unhealthy or die in response to supplements of the usual limiting resources, such as water and nitrogen. We found, however, that the tripartite cyanobacterial lichen Lobaria pulmonaria doubled in annual biomass growth after a single 20-minute immersion in a phosphorus solution (K2HPO4), as compared to controls receiving no supplemental phosphorus. This stimulation of cyanolichens by phosphorus has direct relevance to community and population ecology of lichens, including improving models of lichen performance in relation to air quality, improving forest management practices affecting old-growth associated cyanolichens, and understanding the distribution and abundance of cyanolichens on the landscape. Phosphorus may be as important a stimulant to cyanobacterial-rich lichen communities as it is to cyanobacteria in aquatic ecosystems.

Atmospheric deposition of sulfur (S) and nitrogen (N) has decreased steadily in the northeastern U.S. since the federal 1970 Clean Air Act was passed, yet deposition remains elevated above natural background levels throughout the region. Epiphytic macrolichens are highly sensitive to air pollution and their status is a good indicator of ecological health. We used deposition modeling for 2000–2013 and multiple metrics of lichen status (i.e., species composition, species richness, thallus condition, lichen sensitivity indices, lichen elemental analysis) to assess air pollution effects at 24 plots in four federally-mandated Class I areas. The areas (Lye Brook Wilderness, VT; Great Gulf and the Presidential Range-Dry River Wildernesses, NH; and Acadia National Park, ME) encompass a range of high to low deposition sites. We developed thallus condition scores and sensitivity groups and indices for S and N based on species patterns using deposition estimates gleaned from a larger, independent data base....

Nitrogen-fixing lichens (cyanolichens) are an important source of nitrogen (N) in Pacific Northwest forests, but limitation of lichen growth by elements essential for N fixation is poorly understood. To investigate how nutrient limitation may affect cyanolichen growth rates, we fertilized a tripartite cyanobacterial lichen (Lobaria pulmonaria) and a green algal non-nitrogen fixing lichen (Usnea longissima) with the micronutrients molybdenum (Mo) and vanadium (V), both known cofactors for enzymes involved in N fixation, and the macronutrient phosphorus (P). We then grew treated lichens in the field for one year in western Oregon, USA. Lichen growth was very rapid for both species and did not differ across treatments, despite a previous demonstration of P-limitation in L. pulmonaria at a nearby location. To reconcile these disparate findings, we analyzed P, Mo, and V concentrations, natural abundance δ15N isotopes, %N and change in thallus N in Lobaria pulmonaria from both growth experiments. Nitrogen levels in deposition and in lichens could not explain the large difference in growth or P limitation observed between the two studies. Instead, we provide evidence that local differences in P availability may have caused site-specific responses of Lobaria to P fertilization. In the previous experiment, Lobaria had low background levels of P, and treatment with P more than doubled growth. In contrast, Lobaria from the current experiment had much higher background P concentrations, similar to P-treated lichens in the previous experiment, consistent with the idea that ambient variation in P availability influences the degree of P limitation in cyanolichens. We conclude that insufficient P, Mo, and V did not limit the growth of either cyanolichens or chlorolichens at the site of the current experiment. Our findings point to the need to understand landscape-scale variation in P availability to cyanolichens, and its effect on spatial patterns of cyanolichen nutrient limitation and N fixation.

Lichen symbioses represent a major way of life among the Fungi. Almost one-fifth of all known fungal species are lichenized, and about 1500 species of lichens contain cyanobacterial photobionts, most of which belong to the genus Nostoc . Despite extensive studies, many basic aspects of their biology remain poorly known, especially cyanobiont diversity and specificity ([1][1]). Cyanolichen specimens were collected from northern Europe, western North America, and central China. Epiphytic lichen communities in two old-growth forests in central Finland were studied in detail (tables S1 and S2). Lichens were identified, and free-living cyanobacteria were cultured from substrate samples. The small subunit (16 S ) of the ribosomal gene repeat and the tRNALeu (UAA) intron were sequenced from cyanobacterial DNA. The 16 S rDNA sequences were used to resolve phylogenetic relationships, and the tRNALeu intron sequences were used for identifying Nostoc strains ([2][2]). Cyanobacterial 16 S rDNA sequences were obtained from 16 species of cyanolichens. Additional sequences were acquired from cyanobacterial cultures and GenBank (table S1). A phylogenetic analysis of these sequences resulted in a consensus tree in which all Nostoc formed a monophyletic group with 100% support ([Fig. 1][3]). The Nostoc clade was divided into two subgroups; the first only included cyanobionts of epiphytic lichen species ( Nephroma guild). Further subdivisions within this group did not correlate with the geographical origin or generic identity of the lichen specimens. The second subgroup ( Peltigera guild) included cyanobionts of terrestrial lichens, free-living Nostoc strains, and a symbiotic Nostoc from the roots of a cycad ([Fig. 1][3]). ![Figure 1][4] Figure 1 A strict consensus tree showing phylogenetic relationships among symbiotic and free-living cyanobacteria based on 16 S rDNA sequence data (table S1). Bootstrap support >50% is shown at nodes. All Nostoc strains form a monophyletic group. The cyanobionts of the Nephroma guild form a well-supported subgroup within the Nostoc clade. The cyanobionts of the Peltigera guild group together with free-living Nostoc strains. These groupings are congruent with data from tRNALeu (UAA) intron sequences (table S2). Most epiphytic cyanolichens in central Finland contained similar tRNALeu intron genotypes (table S2). One intron genotype was found from all six sample plots, and it was shared extensively by four different species of Nephroma and Parmeliella . Two other intron genotypes differed from the most frequent intron genotype by only one base change each; these genotypes were found from several epiphytic lichens on different sample plots. These and a fourth Finnish intron genotype shared the same repeat motif in their P6b element ([3][5]). Four North American and two Chinese intron genotypes also had this repeat motif. As in Finland, all these sequences were obtained from epiphytic cyanolichens (table S2). A different set of tRNALeu intron genotypes was obtained from Peltigera thalli and cultured Nostoc strains (table S2). These sequences had a different repeat motif in the P6b element and could not be readily aligned with the sequences from epiphytic cyanolichens ([3][5]). Species of Peltigera are predominately terricolous, and when growing epiphytically, they are usually confined to mossy basal trunks. Two intron genotypes were obtained by culturing thallus fragments of Lobaria pulmonaria . Two North American and two Chinese intron genotypes had the same P6b repeat motif as Finnish Peltigera cyanobionts. As in Finland, these sequences were amplified from different species of Peltigera and Lobaria (table S2). Although lichen mycobionts are selective in their choice of Nostoc symbionts, several fungi may often share identical cyanobiont strains ([1][1], [3][5], [4][6]). Our results demonstrate the full extent of this phenomenon and indicate that cyanolichens express their Nostoc specificity on a community scale. Many cyanolichens associated with old-growth forests depend on a specific group of Nostoc strains that have not been found in other types of cyanolichens. These epiphytes exploit a common pool of cyanobacteria and form a horizontally linked system, the Nephroma guild. Conversely, many terrestrial cyanolichens share a different group of related Nostoc strains, thus forming the Peltigera guild. The guild membership of Finnish Lobaria pulmonaria specimens remained unclear because of inherent uncertainties in identifying symbiotic Nostoc strains by using cultures. North American L. pulmonaria specimens belonged to the Nephroma guild ([Fig. 1][3]). The dispersal ecology of cyanolichen guilds may center around “core species,” such as N. parile and P. triptophylla , that produce massive amounts of symbiotic diaspores. “Fringe species,” such as N. bellum and N. resupinatum , produce only fungal spores and may largely depend on the core species for the dispersal of appropriate cyanobionts. Only a small proportion of symbiotic propagules can develop into mature lichen thalli. Many diaspores land on suboptimal substrates, eventually disintegrate, and release their cyanobionts. These cyanobionts may be salvaged by the mycobionts of fringe species. Core species may also benefit from this activity, as their cyanobionts are deposited into other guild members rather than being completely lost. Some of the cyanobionts can potentially be reclaimed because, without the ability to produce symbiotic diaspores, fringe species cannot “grab the cyanobionts and run.” These phenomena may help to explain why the existence of competition is often difficult to demonstrate in lichen communities ([5][7]). In addition to the two cyanolichen guilds discussed here, we have preliminarily identified several other cyanolichen guilds. Similar systems may also operate among green algal lichens and other symbiotic systems, such as corals. 1. [↵][8]J. Rikkinen, in Cyanobacteria in Symbiosis , A. N. Rai et al. , Eds. (Kluwer Academic, in press). 2. [↵][9]Supporting material is available on Science Online. 3. [↵][10]P. Paulsrud, thesis, Uppsala University, Uppsala, Sweden (2001). 4. [↵][11]1. P. Paulsrud 2. et al. , New Phytol. 152, 117 (2001). 5. [↵][12]1. J. Rikkinen , Bryobrothera 4, 170 (1995). 6. We thank B. McCune, K. Sivonen, and P. Lindblad for cooperation and help. We are especially grateful to P. Paulsrud, who has pioneered the use of molecular methods in the study of lichenized cyanobacteria. Our research was supported by the Academy of Finland (project number 168 332). Supporting Online Material [www.sciencemag.org/cgi/content/full/297/5580/357/DC1][13] Materials and Methods Tables S1 and S2 [1]: #ref-1 [2]: #ref-2 [3]: #F1 [4]: pending:yes [5]: #ref-3 [6]: #ref-4 [7]: #ref-5 [8]: #xref-ref-1-1 "View reference 1 in text" [9]: #xref-ref-2-1 "View reference 2 in text" [10]: #xref-ref-3-1 "View reference 3 in text" [11]: #xref-ref-4-1 "View reference 4 in text" [12]: #xref-ref-5-1 "View reference 5 in text" [13]: http://www.sciencemag.org/cgi/content/full/297/5580/357/DC1

Erioderma pedicellatum (Hue) P.M. Jorg is a globally rare, foliose cyanolichen known from Scandinavia and southeastern Canada. In August 2007, several thalli of E. pedicellatum were collected in Denali National Park and Preserve on the south side of the Alaska Range, Alaska, USA. Subsequently, several additional thalli were observed in nearby Denali State Park. Together they represent the first report of E. pedicellatum within the United States and western North America and mark a major range extension for one of the most rare and endangered lichens in the world. The existence of a third global population center raises intriguing questions about the nature of the genetic relationships among eastern North American, western North American and Scandinavian populations.

Pyrenocollema japonicum H. Harada is described as new on the basis of a specimen from Iwate-ken, northern Japan. It is characterized by having a purplish-brown, smooth thallus; + sessile (or immersed only at base), + globose, black perithecia without thalline cover; I-septate ascospores (20 x 5 ,im); and ellipsoid pycnoconidia (2-3 x ca 1 ,im). It occurs on periodically submerged rocks in forested gorges. Pyrenocollema had long been considered as a monotypic genus with the only species-P. tremelloides Reinke (Zahlbruckner 1924, 1926). In recent decades, however, many species have been transferred from Arthopyrenia (Arthopyreniaceae) and Verrucaria to Pyrenocollema (Coppins et al. 1992; Tucker & Harris 1980). The genus is now regarded as a pyrenocarpous cyanolichen of uncertain taxonomic position, with about 10 species from a wide variety of habitats including maritime (intertidal zone on seashore), freshwater (on rocks in rivers), and terrestrial (Hawksworth et al. 1995; Purvis et al. 1992). They are known mainly from Europe and North America, and only a single maritime species, Pyrenocollema sublitorale (Leight.) A. Fletcher has been recorded for Japan (Santesson 1940, as Arthopyrenia sublitoralis). During a field trip for my taxonomic study of pyrenocarpous lichens in northern Japan, a freshwater species of this genus was collected on riverside rocks in Iwate-ken on the Pacific side of northern Honshu. It differs from all the previously known species of this genus and is here described as new. MATERIALS AND METHODS The description of external morphology is based on airdried material. For anatomical observations, sections were made with a razor blade under a dissecting stereomicroscope. GAW (glycerol:ethanol:water = 1: 1: 1) preparations of sections were used for color description. By replacing the medium of GAW preparations to water, ethanol and finally lactophenol cotton-blue (LPCB), LPCB preparations were made for anatomical drawings, photographs, and descriptions. The K, I, and KI tests were conducted on sections of perithecia and thallus by using ca 10% aqueous solution of KOH and/or a diluted Lugol's solution. The specimen used in this study is deposited in the herbarium of Natural History Museum and Institute, Chiba (CBM).

In the Oregon Cascades, epiphytic cyanolichens are abundant in old-growth forest canopies, but they accumulate very slowly in young forests. We evaluated whether epiphytic cyanolichens require old growth and/or thick, underlying moss mats to achieve normal rates of growth and mortality. We transplanted over one thousand mature thalli of two old-growth associated species (Lobaria oregana and Pseudocyphellaria rainierensis) into the crowns of Douglasfir trees in thirteen forest stands representing four age classes: old-growth (400-700 yr), mature (140-150 yr), young (35-40 yr), and recent clearcut. Wooden racks were used instead of trees in the clearcuts. Half of the cyanolichen thalli were transplanted onto thick moss mats and half were transplanted onto bare bark. After one year, both species grew at least as well in younger forests as they did in old growth (20 to 30% increase in mass), but growth rates were significantly lower in clearcuts. Mortality rates were very low (

Cyanopyrenia japonica Harada, gen. et sp. nov. is described. It is characterized by having a coccoid cyanobiont, perithecia, sparsely branched paraphyses, thin-walled bitunicate asci, and simple hyaline spores. It resembles Verrucaria, Pyrenocollema, and some Lichinaceae in certain morphological respects, but has no clear affinities. It is known only from the type locality in Shikoku, southwestern Japan, where it grows on frequently submerged rocks in the main flow of a river.

A total of 65 epiphyte species (macrolichens, bryophytes, and a fern) were found on the branches offour 700-year-old Douglasfir trees, two growing in theforest interior and two growing on the edge of a 20-year-old clearcut. The moss Antitrichia curtipendula and the cyanolichen Lobaria oregana dominated the epiphyte assemblages. Branch epiphyte assemblages were similar to those reported for a 450-year-old Douglas fir forest, but A. curtipendula and Pseudocyphellaria rainierensis were much more abundant in the older forest. Epiphyte species tended to be positively associated with other members of their functional group. Alectorioid and "other" lichens tended to be negatively associated with bryophytes. Several species were closely associated with moss mats. Ordination revealed one dominant gradient in epiphyte composition that was correlated with height. The gradient could be partitioned into an exposed portion with high lichen cover and low bryophyte cover, an intermediate portion, and a sheltered portion dominated by bryophytes. Biomass and species richness of macrolichen litterfall did not differ between the forest interior and clearcut edge, but there were some differences in the vertical distributions of epiphytes. The exposed and intermediate portions of the compositional gradient extended farther down in the crowns of the edge trees. After two decades of exposure on a clearcut edge, moss mats and associated species were still widely distributed within the edge tree crowns. A considerable amount of canopy epiphyte research has occurred in old-growth Douglas fir forests since the pioneering work of Denison (1973), including an extensive floristic survey of canopy epiphytes (Pike et al. 1975), a detailed examination of the components of individual tree crowns (Pike et al. 1977), an analysis of the distribution of epiphytes within a watershed (Howe 1978), an experiment on cyanolichen growth rates in the canopy (Sillett 1994), and comparisons between old-growth and younger forests (McCune 1993a; Neitlich 1993). These last two studies demonstrated that both biomass and diversity of canopy epiphytes, especially cyanolichens and bryophytes, increase with increasing stand age. McCune (1993a) noticed that Douglas fir canopy epiphytes could be classified into functional groups based on both their ecological roles and their patterns of vertical distribution during forest succession. Bryophytes and cyanolichens, or nitrogen-fixing lichens, were only prevalent in oldgrowth forests, where they occupied the lower and middle portions of tree crowns, respectively. Alectorioid lichens, or forage lichens, and other nonnitrogen fixing lichens (hereafter "other" lichens) were prevalent in younger forests as well as oldg owth forests, where they occupied the upper portion of tree crowns. The old-growth forests studied by Denison, Pike, McCune, and Neitlich were all between 400 and 500 years old and located within the H. J. Andrews Experimental Forest. Aside from Sillett (1994), there are few if any, published studies of canopy epiphytes from old-growth Douglas fir forests located outside of this single watershed in western Oregon. In the Pacific Northwest, management for timber production has converted large areas of old-growth 0007-2745/95/301-312$1.35/0 This content downloaded from 157.55.39.144 on Wed, 21 Sep 2016 05:38:03 UTC All use subject to http://about.jstor.org/terms 302 THE BRYOLOGIST [VOL. 98 TABLE 1. Descriptions of four approximately 700-year-old Douglas fir trees selected for epiphyte sampling in western Oregon. The dagger (t) indicates that tree 3 had recently lost at least 10 m of its top. Both the average and maximum diameters of the 0.5 m axis segments sampled in each tree are listed. Total sampling length is the estimated length of all living branch axes with diameters greater than 7 cm. All measurements are in m. Trunk Number Average Maximum Total Area of Total diameter of living axis axis sampling Sampling Tree forest height at 1.5 m branches diameter diameter length intensity 1 interior 66 2.1 106 0.12 0.29 103 0.243 2 interior 68 2.8 70 0.20 0.37 120 0.108 3 edge 55t 2.4 69 0.11 0.20 165 0.152 4 edge 66 2.0 106 0.10 0.19 93 0.118 forest into a mosaic of remnant forest patches surrounded by clearcuts and regenerating vegetation. The area of interior forest has been dramatically reduced while edge habitats have been proliferated (Spies et al. 1994). Edges of old-growth forests bordering clearcuts are characterized by drier microclimates and higher rates of large tree mortality compared to the forest interior (Chen et al. 1992, 1993). Very little is known about the impacts of these changes on epiphytes, although several endemic epiphyte species appear to be closely associated with old-growth Douglas fir forests (USDA 1994; Neitlich 1993). This study is the first to investigate canopy epiphytes in a Douglas fir forest well over 500 years old. Branches were sampled in large trees growing in the forest interior and on the edge of a clearcut. Epiphyte litterfall was also sampled in these two areas of the forest. There were four principle objectives: 1) analysis of within-tree structure of branch epiphyte assemblages, 2) elucidation of major compositional gradients in epiphyte assemblages, 3) floristic comparison of epiphytes between 700-yearold and 450-year-old Douglas fir canopies, and 4) a comparison between epiphytes of a forest interior and a clearcut edge.

Thalli of two epiphytic lichens, Lobaria oregana (Tuck.) Miill. Arg. and Pseudocy- phellaria rainierensis Imsh., were collected from the canopy of an old-growth forest. Thalli were individually attached to nylon monofilament and transplanted into the crowns of four trees, two growing in the forest interior and two growing on the edge of a clearcut, at heights between 35 and 45 m above the ground. Half of the transplants in each tree were derived from thalli collected in the interior and half were derived from thalli collected on the edge. After one year, L. oregana transplants grew significantly less on the edge than they grew in the interior. The source of P. rainierensis thalli significantly affected transplant growth rate. Thalli that came from the interior and were transplanted to the edge did not grow, on average, while thalli that came from the edge and were transplanted back to the edge grew well.

Epiphyte biomass on branches and trunks was estimated for 42 individual felled trees, distributed among three Pseudotsuga menziesii-Tsuga heterophylla stands aged 95, 145, and 400+ years, in the western Cascade Range of Oregon and Washington, then extrapolated to the whole stands by regression techniques. Epiphytes were sorted into four groups defined by ecological roles rather than taxonomy: cyanolichens, alectorioid lichens, other lichens, and bryophytes. In general the spatial sequence of dominance of these four groups, from upper canopy to forest jloor, was: "other" lichens, alectorioid lichens, cyanolichens, and bryophytes. The zones of these functional groups of epiphytes apparently migrate upward in forests through time. For example the Hypogymnia and Platismatia that dominate throughout canopies in young forests are found primarily in the upper canopies of old forests. Similarly, bryophytes enter a stand near the forest jloor and gradually expand their dominance upwards. Epiphyte biomass was greatest in the old-growth stand, with about 2.6 t/ha. In the two younger stands total epiphyte biomass was about 1 t/ha. The old-growth stand differed from the younger stands in having over 1 t/ha of cyanolichens, while this group was essentially absent from the younger stands. As a synthesis of these and previous results, a similar gradient hypothesis is proposed: epiphyte species are ordered similarly on three distinct spatial and temporal gradients: 1) vertical differences in species composition within a given stand, 2) species compositional differences among stands differing in moisture regime but of the same age, and 3) changes in species composition through time in a given stand.

Free-living and lichenized cyanobacterial (cyanolichen) colonies occupy 12-29% of the surface area in the Sand Hills grasslands on the Arapaho Prairie in southwestern Nebraska. During brief periods of favorable conditions (i.e., moderate temperature and high moisture), these diazotrophs are capable of high rates of dinitrogen fixation. Maximum rates of acetylene reduction measured during 1981 and 1982 were 2,237 ,g N m-2 hr. The duration of dinitrogen fixation activity is dependent upon moisture conditions; rates of acetylene reduction were shown to decline 90% in as little as three hr. Desiccated colonies resumed acetylene reduction activity within one hr and achieved equilibrium rates within four hr following rehydration. Associative, heterotrophic diazotrophs were isolated from the rhizospheres of several grass species. These bacteria exhibited a range of culturing characteristics which may reflect differing plant-bacterial interaction potentials important to the establishment and maintenance of the plant species. None of the field assays for heterotrophic dinitrogen fixation performed over the two-yr period indicated a capacity of this group to provide ecologically significant levels of N

In contrast to lichens with green photobionts, the bionts of cyanolichens are difficult to culture and synthesize under laboratory conditions. Problems include difficulties in obtaining growth of the mycobionts, achieving axenic cultures of the photobiont, and maintaining mixed biont cultures for long periods of time.

Four fruticose lichens of different genera, all belonging to the cyanolichen familyLichinaceae were studied by ultrathin sectioning and freeze-fracturing/-etching in order to see details in the structure of the photobiont-mycobiont interface. Within the haustorial region, the fibrillar sheath of the photobiont was almost absent and the thickness of the fungal cell wall was strongly reduced.

Dry lichen thalli were enclosed in gas exchange chambers and treated with an air stream of high relative humidity (96.5 to near 100%) until water potential equilibrium was reached with the surrounding air (i.e., no further increase of weight through water vapor uptake). They were then sprayed with liquid water. The treatment took place in the dark and was interrupted by short periods of light. CO2 exchange during light and dark respiration was monitored continuously. With no exception water uptake in all of the lichen species with green algae as phycobionts lead to reactivation of the photosynthetic metabolism. Further-more, high rates of CO2 assimilation were attained without the application of liquid water. To date 73 species with different types of Chlorophyceae phycobionts have been tested in this and other studies. In contrast, hydration through high air humidity alone failed to stimulate positive net photosynthesis in any of the lichens with blue-green algae (Cyanobacteria). These required liquid water for CO2 assimilation. So far 33 species have been investigated, and all have behaved similarly. These have included gelatinous as well as heteromerous species, most with Nostoc phycobionts but in addition some with three other Cyanophyceae phycobionts. The same phycobiont performance differences existed even within the same genus (e.g. Lobaria, Peltigera) between species pairs containing green or blue-green phycobionts respectively. Free living algae also seem to behave in a similar manner. Carbon isotope ratios of the lichen thalli suggest that a definite ecological difference exists in water status-dependent photosynthesis of species with green and blue-green phycobionts. The underlying biochemical or biophysical mechanisms are not yet understood. Apparently, a fundamental difference in the structure of the two groups of algae is involved.

Interactions within lichen communities include, in addition to close mutualistic associations between the main partners of specific lichen symbioses, also more elusive relationships between members of a wider symbiotic community. Here, we analyze association patterns of cyanolichen symbionts in the tropical montane forests of Taita Hills, southern Kenya, which is part of the Eastern Afromontane biodiversity hotspot. The cyanolichen specimens analyzed represent 74 mycobiont taxa within the order Peltigerales (Ascomycota), associating with 115 different variants of the photobionts genus Nostoc (Cyanobacteria). Our analysis demonstrates wide sharing of photobionts and reveals the presence of several photobiont-mediated lichen guilds. Over half of all mycobionts share photobionts with other fungal species, often from different genera or even families, while some others are strict specialists and exclusively associate with a single photobiont variant. The most extensive symbiont network involves 24 different fungal species from five genera associating with 38 Nostoc photobionts. The Nostoc photobionts belong to two main groups, the Nephroma-type Nostoc and the Collema/Peltigera-type Nostoc, and nearly all mycobionts associate only with variants of one group. Among the mycobionts, species that produce cephalodia and those without symbiotic propagules tend to be most promiscuous in photobiont choice. The extent of photobiont sharing and the structure of interaction networks differ dramatically between the two major photobiont-mediated guilds, being both more prevalent and nested among Nephroma guild fungi and more compartmentalized among Peltigera guild fungi. This presumably reflects differences in the ecological characteristics and/or requirements of the two main groups of photobionts. The same two groups of Nostoc have previously been identified from many lichens in various lichen-rich ecosystems in different parts of the world, indicating that photobiont sharing between fungal species is an integral part of lichen ecology globally. In many cases, symbiotically dispersing lichens can facilitate the dispersal of sexually reproducing species, promoting establishment and adaptation into new and marginal habitats and thus driving evolutionary diversification.