Diploschistes Muscorum Research Articles

Metabolic processes involved with sugar alcohol and secondary metabolite production in the hyperaccumulator lichen Diploschistes muscorum reveal its complex adaptation strategy against heavy-metal stress

The synthesis of various unique secondary metabolites by lichens is the result of mutualistic symbiotic association between the mycobiont and autotrophic photobiont. The function of these compounds and causal factors for their production are not fully understood. This paper examines the effect of heavy-metal bioaccumulation and physiological parameters related to photosynthesis and carbon metabolism on the production of lichen substances in hyperaccumulator Diploschistes muscorum. The obtained model of secondary metabolite concentrations in the thalli demonstrates that the carbon source provided by the photobiont and associated polyols produced by the mycobiont have positive impact on the production; on the contrary, the increased intracellular load of heavy metals and excessive loss of cell membrane integrity adversely affected secondary metabolite contents. Additionally, the production of secondary metabolites appears to be more dependent on intracellular metal concentrations than on soil pollution level. To compensate for metal stress, both efficient functioning of algal component and sufficient production of secondary metabolites are required. The balanced physiological functioning of mycobiont and photobiont constitutes the complex protective mechanism to alleviate the harmful effects of heavy metal stress on primary and secondary metabolism of lichens.

Porosty cynkowo-ołowiowych terenów pogórniczych w Jaworznie

The paper presents the occurrence of 69 lichen species in calamine areas in Jaworzno town, including 47 taxa in the Ciężkowice area, 32 in Długoszyn and 38 in Sadowa Góra. Six lichen species are red-listed in Poland. Rare species characteristic of zinc- and lead-enriched substrates were found: Agonimia vouauxii, Diploschistes muscorum, Sarcosagium campestre, Vezdaea aestivalis and V. leprosa.

Lichen-forming fungi in postindustrial habitats involve alternative photobionts

ABSTRACT Mycobionts of many lichen genera appear to demonstrate strong selectivity in the choice of algal partner. The biological properties of a photobiont and its availability in an environment significantly determine the habitat requirements of lichens. Flexibility in photobiont choice extends the ecological amplitude of lichens; therefore, it may constitute an important adaptive strategy for colonization of extreme habitats. The photobiont inventory of the three epigeic lichens most resistant to soil pollution, i.e., Cladonia cariosa, C. rei, and the hyperaccumulator Diploschistes muscorum, was examined to verify whether and to what extent algal composition depends on the type of habitat and substrate enrichment with heavy metals. Photobionts Asterochloris and Trebouxia were identified in the studied lichen species; however, the presence of Trebouxia was directly related to anthropogenic sites with technogenic substrates, and the proportion of lichen specimens with these algae clearly depended on the level of heavy-metal soil pollution and the habitat type. The total number of algal haplotypes increased with increasing soil pollution, and the richness was associated more with soil pollution than with a given lichen species. Additionally, a large number of lichen individuals bearing multiple algal genotypes at polluted sites were recorded. Although Cladonia lichens were previously thought to be restricted to Asterochloris, they are able to start the relichenization process with Trebouxia under specific habitat conditions and to establish a stable association with these algae when colonization of disturbed sites takes place. Comparative analysis of the internal transcribed spacer (ITS) rDNA sequences revealed as many as 13 haplotypes of Trebouxia, and phylogenetic analysis grouped them into two different clades. Such a high level of genetic diversity indicates that Trebouxia is well adapted to metal pollution and could be an alternative photosynthetic partner for certain lichens, especially in polluted sites.

Heavy-metal pollution induces changes in the genetic composition and anatomical properties of photobionts in pioneer lichens colonising post-industrial habitats

Certain lichens are effective colonisers of polluted sites. However, little is known about the tolerance of photobionts and the degree of mycobiont selectivity to photobionts relative to metal pollution. The present study recognises the genetic and anatomical diversity of Asterochloris photobionts in epigeic lichens, i.e. Cladonia cariosa, C. rei, and Diploschistes muscorum, in relation to a wide spectrum of soil pollution. In accordance with phylogenetic analysis, photobionts were clustered in 7 moderately- to well-supported clades, including 19 haplotypes. The mycobionts of all studied lichens demonstrated a low level of selectivity and were capable of associating with various Asterochloris lineages. This tendency was also expressed by the frequent (~25%) occurrence of multiple algal genotypes in a single thallus. This indicates that identified Asterochloris lineages are generally tolerant to heavy-metal pollution, and the low level of selectivity of mycobionts enables them to select the most suitable and/or available partner. The trend of increasing incidence of certain Asterochloris lineages and decreasing frequency of others along with increasing soil pollution was observed. This proves the superior adaptation of some photobionts to polluted sites. Such symbiotic plasticity constitute an adaptive feature necessary for the successful colonisation. High number of haplotypes at polluted sites could be the result of multiple introduction events from different areas during the initial stages of spontaneous succession. Regardless of the genetic pattern, Asterochloris cells were considerably smaller, and the density and compaction of cells in the algal layer were higher, in lichen specimens from polluted sites, indicating that photobiont characteristics may be closely dependent on heavy-metal pollution.

The bright and shaded side of duneland life: the photosynthetic response of lichens to seasonal changes is species-specific

Terricolous lichens are relevant associates of biological soil crusts in arid and semiarid environments. Dunes are ecosystems of high conservation interest, because of their unique, vulnerable and threatened features. The function of lichens is affected by the changing seasons and different microhabitat conditions. At the same time, inland dunes are less investigated areas from the terricolous lichens point of view. We explored the effect of seasonal variation and different micro-environmental conditions (aspect) on the metabolic activity of five terricolous lichen species, representing various growth forms, in temperate semiarid grasslands. Populations of Cladonia foliacea, C. furcata, C. pyxidata group, Diploschistes muscorum and Thalloidima physaroides were investigated. Thalli sampled from the south-west and north-east facing microhabitats were studied by chlorophyll fluorescence analysis for 2 years. The present study aims to understand how changing climate (during the year) and aspect affect photosynthetic activity and photoprotection. Microclimatic data were also continuously recorded to reveal the background of the difference between microhabitat types. As a result, the air temperature, photosynthetically active radiation, soil temperature and vapour pressure deficit were significantly higher on south-west than on north-east facing microsites, where relative humidity and water content of soil proved to be considerably higher. Higher photosynthetic activity, as well as a higher level of photoprotection, was detected in lichens from north-east-oriented microsites compared with south-west populations. In addition, the difference between sun and shade populations varied seasonally. Since a species-specific response to both aspect and season was detected, we propose to investigate more than one species of different growth forms, to reveal the response of lichens to the changing environment in space and time.

Heavy-metal tolerance of photobiont in pioneer lichens inhabiting heavily polluted sites

Heavy metals are known for their negative impact on the physiological processes of lichen photobiont. In spite of this, certain lichens are known to be effective pioneers of polluted sites. Cladonia cariosa, C. rei, and Diploschistes muscorum are prominent examples of lichens that spontaneously colonise post-industrial wastes. We examined the effect of total and intracellular Zn, Pb, Cd, As, Cu, and Ni accumulation in the thalli of these species on the physiological parameters of photobiont. Increased accumulation of Zn, Cd, Cu, and Ni in D. muscorum and of Zn and Ni in C. rei negatively affected contents of photosynthetic pigments, whereas concentrations of Pb had a positive effect in all lichen species. Moreover, pigment contents were positively associated with the concentrations of most examined elements in C. cariosa. The results indicate that even if chlorophyll contents reduced, its degradation does not progress. This suggests that metal stress may exert a negative effect on the synthesis rather than on the integrity of chlorophyll. Most importantly, lichen samples of each of the species from polluted sites proved to possess significantly higher FV/FM ratios than those from a reference site; moreover, the contents of elements of lichen thalli positively influenced this parameter. The efficient functioning of the algal component under heavy-metal stress conditions indicates that the examined lichens are well adapted to extremely contaminated substrates.

Biological soil crust diversity and composition in southwest Idaho, U.S.A.

Biological soil crusts (BSCs) were sampled by habitat types within and adjacent to the Orchard Combat Training Center (OCTC) in southwest Idaho, U.S.A. Plots consisting of a 34.7 m radius circle, approximately equal to one acre or 0.38 hectares were sampled. We focused on five native vascular plant-dominated current habitat types within the OCTC, including: 1) Wyoming sagebrush, 2) saltbush, 3) rabbitbrush, 4) winterfat, and 5) Sandberg bluegrass. We describe how BSC cover and species richness varied with habitat types in the study area. We recorded the relative abundance of BSCs and vascular plant species and collected voucher specimens for each BSC. The biodiversity of each BSC in these arid habitat types was much greater than many ecologists have assumed. We found a total of 68 species of BSC across all 17 plots. BSC cover differed significantly across the different habitat types. BSC cover was significantly higher in sagebrush and saltbush as compared with Poa, rabbitbrush and winterfat habitat types. Overall, there was substantially more BSC richness (17–47 species) than vascular plant richness (4– 13 species), and BSC richness was positively related to vascular plant richness (R2=0.18, p=0.041). On average, each additional plant species was associated with 1.36 additional BSC species. BSC communities also varied across the habitat types with Buellia punctata as a significant indicator species for sagebrush, Toninia sedifolia for saltbush, and Cladonia pocillum for winterfat. Several BSC species were associated with 2 or 3 habitat types; for example, Cladonia fimbriata, Diploschistes muscorum, Leptogium lichenoides, Massalongia carnosa, Riccia sorocarpa and Trapeliopsis steppica were most common in the sagebrush, Poa, and rabbitbrush habitats. In contrast, Caloplaca tominii, Endocarpon loscosii, Placidium squamulosum and Psora tuckermanii were most common in winterfat and saltbush habitats.

LICHENS AND LICHENICOLOUS FUNGI OF NATIONAL NATURE PARKS «NYZHNOSULSKY» AND «PYRYATYNSKY»

Introduction. Currently, the protected areas of the Poltava region remain poorly understood. Purpose. This is a comprehensive study of the lichens and lichenicolous fungi on the territory of two National Nature Parks (NNPs). Methods. Collecting was carried out by the route­expedition method. Lichens and lichenicolous fungi were identifid in accordance with a standard procedure. Results. NNP «Nyzhnyo sulsky» was represented by 54 species of the lichens and 6 species of the lichenico lous fungi. 55 species of the lichens and 4 species of the lichenicolous fungi were found on the territory of the NNP «Pyryatynsky». Corticolous lichens are dominant ecological groups in both National Nature Parks. 50 corticolous species (92 %) were found in NNP «Nyzhnyosulsky» and 46 species (82 %) were found in NNP «Pyryatynsky». These species are confied to the growth on the bark of the hardwood trees, especially Betula, Populus, Robinia and Quercus. The mature oaks are the most valuable lichen habitat in the parks. Such species as Arthonia mediella, Bacidia rubella, Caloplaca obscurella, Candelariella faginea, Chaenotheca trichialis, Dimerella pineti, Graphis scripta, Pachyphiale carneola have been found rarely on the oak bark on the plain part of Ukraine. Among them A.mediella, C. obscurella and D. pineti are first time reported for the Left­Bank Forest­Steppe zone of Ukraine. The bark of Populus nigra is a habitat for a few rare species, such as Arthrosporum populorum, Lecania fuscella, Piccolia ochrophora and Rinodina pityrea. Rare species in Ukrainian plain A. cinereopruinosa, Buellia griseovirens, Lecanora symmicta, Parmeliopsis ambigua, Trapeliosis granulosa, Vulpicida pinastri were found on the bark of Betula verru cosa in NNP «Pyryatynsky». A. cinereopruinosa is a new one for Left Bank ForestSteppe zone. Seven species of lichens (A. populorum, B. griseovirens, P. argena, P. ochrophora, R. pityrea, T. granulosa, X. candelaria) and three species of li chenicolous fungi (Athelia arachnoidea, Erythricium aurantiacum, Xanthoriicola physciae) are first time reported for the Poltava region. Terricolous lichens such as Bacidia bagliettoana, Diploschistes muscorum, Mycobilimbia subulatorum and Peltigera didactуla are usually associated with weakly overgrown slopes of the ravines and beams. Terricolous lichens B. bagliettoana and P. didactyla are vulnerable in lowland landscapes of Ukraine and need to be protected at the local level. Lichenicolous fungi Pronectria diplococca on En chylium tenax and Homostegia piggotii on Parmelia sulcata are new for Left Bank Forest Steppe zone. Conclusion. Thus, the species diversity of lichens of both NPPs is typical of the forest steppe zone and needs to be protected.

New or Otherwise Interesting Records of Lichens and Lichenicolous Fungi from Belarus. III. With an Updated Checklist of Lichenicolous Fungi

Abstract: Tsurykau, A. 2017. New or otherwise interesting records of lichens and lichenicolous fungi from Belarus. III. With an updated checklist of lichenicolous fungi. — Herzogia 30: 152–165. Data on 13 species of lichenized and lichenicolous fungi from Belarus are presented; two lichens (Biatora efflorescens and Catillaria croatica) and ten lichenicolous fungi (Abrothallus microspermus, A. suecicus, Arthonia phaeophysciae, Arthrorhaphis aeruginosa, Merismatium decolorans, Phacopsis oxyspora, Polycoccum peltigerae, Pronectria subimperspicua, Taeniolella delicata and Zwackhiomyces echinulatus) are new to the country. Diploschistes muscorum is reported on lichens for the first time from Belarus. An updated checklist of lichenicolous fungi known from Belarus is also provided.

ADDITIONS TO THE LICHEN FLORA OF THE PASVIK STRICT NATURE RESERVE (MURMANSK REGION) BASED ON RECORDS FROM 2015-2016

Although there are many published articles about the lichen flora of the Pasvik Strict Nature Reserve, the diversity of lichen-forming and lichenicolous fungi of this protected area is not completely known. In 2016, the Reserve's administration organized a new hepatic-lichenological field trip to the southern part of the Reserve. One of the main goals of this trip was to study the lichen diversity of old pine and aspen forests. As a result, sixteen species of lichens have been added to the total number of lichens ever found in the Pasvik Reserve (NW Murmansk Region), viz. Anzina carneonivea, Bacidina chloroticula, Blastenia ammiospila, Bryoria implexa, Cetraria nigricans, Cladonia cariosa, C. stricta, Diploschistes muscorum, Leimonis erratica, Multiclavula corynoides, Nephroma resupinatum, Phaeophyscia endococcina, Protomicarea limosa, Strangospora moriformis, Tephromela atra, Trapeliopsis flexuosa. The total lichen flora of the Pasvik Reserve now comprises 504 species. A rare southern species Bacidina chloroticula is new to the Murmansk Region. This species was found in the southern part of the reserve in an old aspen forest, growing on moss-covered rock. A rare species Peltigera occidentalis was found for the second time in the Murmansk Region, in an area adjacent to the Reserve. Anzina carneonivea, Bryoria implexa, Nephroma resupinatum, Peltigera occidentalis, and Trapeliopsis flexuosa are newly reported for the biogeographic province Lapponia petsamoensis. Six genera are new for the lichen flora of the Reserve - Anzina, Leimonis, Multiclavula, Protomicarea, Strangospora, and Tephromela. In addition, nineteen rarely collected species are also reported. Brief characteristics of the localities and notes on regional distribution of the species are given. New localities for three species from the Red Data Books of the Murmansk Region and Russia, Bryoria fremontii, Lichenomphalia hudsoniana and Melanohalea exasperata, are reported. It is recommended to exclude the species Melanohalea exasperata from the Red Data Book of the Murmansk Region as non-threatened.

Pssst…pass the algae: succession in lichen soil crusts

Pssst…pass the algae: succession in lichen soil crusts

Microbiome change by symbiotic invasion in lichens.

Lichens are obligate symbioses between fungi and green algae or cyanobacteria. Most lichens resynthesize their symbiotic thalli from propagules, but some develop within the structures of already existing lichen symbioses. Diploschistes muscorum starts as a parasite infecting the lichen Cladonia symphycarpa and gradually develops an independent Diploschistes lichen thallus. Here we studied how this process influences lichen-associated microbiomes and photobionts by sampling four transitional stages, at sites in Sweden and Germany, and characterizing their microbial communities using high-throughput 16S rRNA gene and photobiont-specific ITS rDNA sequencing, and fluorescence in situ hybridization. A gradual microbiome shift occurred during the transition, but fractions of Cladonia-associated bacteria were retained during the process of symbiotic reorganization. Consistent changes observed across sites included a notable decrease in the relative abundance of Alphaproteobacteria with a concomitant increase in Betaproteobacteria. Armatimonadia, Spartobacteria and Acidobacteria also decreased during the infection of Cladonia by Diploschistes. The lichens differed in photobiont specificity. Cladonia symphycarpa was associated with the same algal species at all sites, but Diploschistes muscorum had a flexible strategy with different photobiont combinations at each site. This symbiotic invasion system suggests that partners can be reorganized and selected for maintaining potential roles rather than depending on particular species.

New records of lichens and allied fungi from the Leningrad Region, Russia. VI

Eighteen species of lichens and five lichenicolous fungi are reported here for the Leningrad Region or Saint Petersburg. Of them, the lichens Absconditella delutula, Calogaya pusilla, Flavoplaca flavocitrina and Rinodina colobina are new for the North-Western European Russia, and the lichenicolous species Abrothallus parmeliarum, Diploschistes muscorum, Lichenochora cf. polycoccoides and Nieslia peltigericola – for the Leningrad Region; Cladonia novochlorophaea and Lichenodiplis lecanorae are reported for the first time for Saint Petersburg. The most noteworthy records are briefly discussed.

Cryptogamic Communities Dominated by the LichenCladonia rei— a Case Study of Polish Post-Smelting Dumps in a Worldwide Context

Rola, K., Osyczka, P. & Nobis, M. 2014. Cryptogamic communities dominated by the lichen Cladonia rei — a case study of Polish post-smelting dumps in a worldwide context. — Herzogia 27: 121–135.Pioneer vegetation is frequently characterised by a high proportion of cryptogamic species, both in natural sites and anthropogenic and disturbed habitats. This study focuses on pioneer communities developing in strongly affected and contaminated sites of post-smelting dumps in Poland. Lichens, bryophytes and vascular plants were examined in study plots within homogenous patches of vegetation. Phytosociological data on cryptogamic associations, with the lichen Cladonia rei as the predominant species, from anthropogenic habitats of Germany and sand dunes in Ukraine were used for comparative purposes. Hierarchical cluster analysis and non-metric multidimensional scaling (NMDS) were employed to investigate cryptogamic vegetation differentiation and detrended correspondence analysis (DCA) was used to identify the distribution patterns of the individual cryptogamic species. Phytosociological data from Europe were additionally compared with data from Canada representing the Cladonietum nemoxynae by means of NMDS analysis. The results show that the Cladonietum rei is a widespread and well-defined association characteristic for anthropogenic sites in Europe. The Cladonietum rei can occur in several variants; in strongly heavy metal contaminated post-smelting dumps in Poland, the association is characterised by the frequent occurrence of Diploschistes muscorum and Cladonia conista. It creates compact, homogenous patches over relatively large areas and certainly is not a synusium only, but rather a distinct pioneer community.

The unusual lichens and allied fungi of Sandbanks Provincial Park, Ontario

Sandbanks Provincial Park contains one of the world’s largest freshwater bay mouth sandbar and dune systems. To better understand the lichen biota of this provincially rare ecosystem, we inventoried the species at Sandbanks and its surrounding area. We found 128 species of lichens and allied fungi in 58 genera. Two species are new to Canada, Hyperphyscia syncolla (Tuck. ex Nyl.) Kalb and Minutoexcipula mariana V. Atienza. One additional species is new to Ontario, Physcia biziana (A. Massal.) Zahlbr. Sixteen species are provincially ranked as S1 (critically imperiled), S2 (imperiled), or S3 (vulnerable) by the Natural Heritage Information Centre: Acrocordia cavata (Ach.) R.C. Harris, Anaptychia crinalis (Schaer.) Vězda, Arthrosporum populorum A. Massal., Bacidia rubella (Hoffm.) A. Massal., Cresponea chloroconia (Tuck.) Egea & Torrente, Diploschistes muscorum (Scop.) R. Sant. ssp. muscorum, Flavopunctelia soredica (Nyl.) Hale, Heterodermia obscurata (Nyl.) Trevis., Lecanora carlottiana Lewis & Śliwa, Leptogium tenuissimum (Dicks.) Körb., Phaeophyscia hirsuta (Mereschk.) Essl., Physconia enteroxantha (Nyl.) Poelt, Ramalina pollinaria (Westr.) Ach., Staurothele drummondii (Tuck.) Tuck., Teloschistes chrysophthalmus (L.) Th. Fr., and Trypethelium virens Tuck. ex Michener. Unranked species collected for the second time in Ontario are Arthonia diffusa Nyl., Cladonia norvegica Tønsberg & Holien, and Lecanora juniperina Śliwa. Other provincially rare and unranked species are Caloplaca pollinii (A. Massal.) Jatta and Xanthomendoza weberi (S. Kondr. & Kärnefelt) L. Lindblom. Of these rare and unranked species, the following are reported (published) for the first time in the province: A. diffusa, C. pollinii, and L. juniperina. Some lichens require specific ecological conditions for colonization, and the rare ecosystem at Sandbanks appears to be the reason for the large number of rare species. We recommend a lichen education program for park visitors to make them more aware of these unusually rare and sensitive lichens in the park.

Lichens of abandoned zinc-lead mines

A list of lichens from areas of zinc-lead ores in Southern Poland and a review of the characteristic lichen biota of these sites is provided. In spite of the devastated and heavy metal contaminated environment, a highly diverse epigeic and epilithic lichen biota was found, including species characteristic of various anthropogenic habitats, particularly zinc and lead enriched substrates (<em>Diploschistes muscorum, Steinia geophana, Sarcosagium campestre, Vezdaea aestivalis</em> and <em>V. leprosa</em>). Also, the high-mountain species <em>Leucocarpia biatorella</em>, as well as very rare in Europe <em>Thelocarpon imperceptum</em>, and several species categorized as very rare, endangered and protected in Poland were recorded. Crustose lichens are the most abundant; among fruticose forms <em>Cladonia</em> spp. predominate and <em>Stereocaulon incrustatum</em> is common.

Response of the lichen Cladonia rei Schaer. to strong heavy metal contamination of the substrate

The phenomenon of mass occurrence of the lichen Cladonia rei in extremely contaminated post-smelting slag dumps was studied in relation to metal accumulation capacity of this lichen. The research was aimed to evaluate the relationships between element contents in the thalli and in the corresponding substrate. The study was conducted in terms of a wide spectrum of Zn, Cd, Pb and As contents. The concentrations of these elements in the lichen thalli and substrate samples were measured. Various regression models were considered to find the best fitted one that greatly reflects the dependencies. Various Cladonia species and the hyperaccumulator Diploschistes muscorum were also included in the study for comparison purposes. Specific non-linear regression models described by a power function reflected relationships between Zn and Cd contents in C. rei thalli and in the host substrate in the most reliable way. The relationship for As was also noted, but none significant model was found. Contrarily, Pb concentrations in the thalli varied independently of the metal levels in the substrate. Nevertheless, the concentrations of all measured heavy metals in C. rei thalli are relatively low considering the frequently enormous substrate contamination. Different Cladonia species demonstrated a generally similar accumulation capacity and could be considered as weak accumulators. The restrained accumulation pattern may be one of the important attributes of C. rei which facilitates its colonisation of extremely contaminated dumps. This finding highlights ecological importance of this species as stable and resistant pioneer in such affected sites.

Bromus tectorum litter alters photosynthetic characteristics of biological soil crusts from a semiarid shrubland

Invasion by the exotic annual grass Bromus tectorum has increased the cover and connectivity of fine litter in the sagebrush steppes of western North America. This litter tends to cover biological soil crusts, which could affect their metabolism and growth. To investigate this possible phenomenon, biological soil crusts dominated by either the moss Bryum argenteum or the lichen Diploschistes muscorum were covered with B. tectorum litter (litter treatment) or left uncovered (control treatment) and exposed to natural field conditions. After periods of five and ten months, we removed the litter and compared the photosynthetic performance of biological soil crusts from the two treatments. Litter induced photosynthetic changes in our samples. In both B. argenteum and D. muscorum, biological soil crusts that had been covered with litter for ten months had lower rates of gross photosynthesis and lower chlorophyll content than control samples. Similarly in both biological soil crust types, litter reduced the rate of dark respiration. For D. muscorum, the reduction in dark respiration fully compensated for the decrease in gross photosynthesis, resulting in similar values of net photosynthesis in the two treatments. In contrast, for B. argenteum, net photosynthesis was four-times greater in the control than the litter treatment. Also under litter cover, D. muscorum showed three common adaptations to shade conditions: a decrease in the light compensation point, in the light intensity needed to achieve 95% of maximal net photosynthesis, and in the chlorophyll a/b ratio. None of these changes was apparent in B. argenteum. Overall, our results indicate that photosynthetic responses to the presence of litter varied among species of the crust biota and that the litter can reduce the photosynthetic capacity of biological soil crusts. These results help to explain field observations of decreases in biological soil crust cover and changes in biological soil crust composition with increases in litter cover, and suggest that the landscape-wide invasion by B. tectorum may have substantial effects on biological soil crust performance and therefore their capacity to function in semiarid shrublands.

Seed water status and root tip characteristics of two annual grasses on lichen-dominated biological soil crusts

Biological soil crusts can affect seed germination and seedling establishment. We have investigated the effect of biological soil crusts on seed water status as a potential mechanism affecting seed germination. The seed water potential of two annual grasses, one exotic Bromus tectorum L. and another native Vulpia microstachys Nutt., were analyzed after placing the seeds on bare soil, on a crust that contains various lichens and mosses (mixed crust), or on a crust dominated by the crustose lichen Diploschistes muscorum (Scop.) R. Sant. (Diploschistes crust). Seed water potential and germination were similar on the bare soil and the mixed crust, except for the initial germination of V. microstachys, which was higher on the mixed crust than on the bare soil. For the two grasses studied, seed water potential was significantly higher on the bare soil and mixed crust than on the Diploschistes crust. These differences in water potential correlated with differences in germination, which was much lower on the lichen crust. Experiments were conducted under two watering regimens. Increasing the frequency of watering amplified the differences in seed water potential and germination between the Diploschistes crust and the other two surfaces. For a particular watering regimen, the bare soil, mixed crust, and Diploschistes crust received the same amount of water, but they reached significantly different water potentials. Throughout the experiments, the water potential of the soil and mixed crust remained above −0.6 MPa, while there was a marked decline in the water potential of the Diploschistes surface to about −4 MPa. To ascertain that water was the major factor limiting germination on the Diploschistes crust, we conducted germination tests in an environment with 100% relative humidity. Under these conditions, germination on the Diploschistes crust was similar to that on the bare soil. However, the seeds that germinated on the Diploschistes crust did not penetrate this surface and approximately 60% of their root tips became necrotic. Our results indicate that the presence of D. muscorum can inhibit seedling establishment by two mechanisms: a reduction in seed water absorption and an increase in root tip mortality.

Germination and seedling establishment of two annual grasses on lichen-dominated biological soil crusts

Biological soil crusts dominated by lichens are common components of shrub-steppe ecosystems in northwestern US. We conducted growth chamber experiments to investigate the effects of these crusts on seed germination and initial seedling establishment of two annual grasses; the highly invasive exotic Bromus tectorum L. and the native Vulpia microstachys Nutt. We recorded germination time courses on bare soil and two types of biological soil crusts; one composed predominantly of the lichen Diploschistes muscorum (Scop.) R. Sant. (lichen crust) and the other comprised of an assortment of lichens and mosses (mixed crust). Final germination on the lichen crust for both grass species was about a third of that on the bare soil surface. Mean germination time (MGT) was 3–4 days longer on the lichen crust compared with the bare soil. In contrast, there was no difference in germination percentage or MGT between the mixed crust and bare soil, and results were similar for both grass species. For both species, root penetration of germinating seeds on the lichen crust was lower than on the bare soil or mixed crust surfaces. The combined effects of the lichen crust on germination and root penetration resulted in an overall reduction in seedling establishment of 78% for V. microstachys and 85% for B. tectorum relative to the bare soil treatment. Our results clearly demonstrate that lichen-dominated biological soil crust can inhibit germination and root penetration, but the extent of these effects depends on the composition of the crust.