Endolithic Research Articles

Fast Reactivation by High Air Humidity and Photosynthetic Performance of Alpine Lichens Growing Endolithically in Limestone

ABSTRACTThis paper is dedicated to Otto Ludwig Lange on the occasion of his 80th birthday. Hymenelia prevostii and H. coerulea are common endolithic lichen species on limestone outcrops in the eastern alpine mountains. We investigated their photosynthetic properties under controlled laboratory conditions and analyzed them with respect to relevant meso- and macroclimatic parameters to determine specific adaptations to the extreme habitat.For the first time, it can be shown that endolithically living lichens are able to utilize water vapor alone to gain positive net photosynthesis (NP) rates. With respect to liquid water, both species reached optimum NP rates at low water content (H. prevostii: 0.26 mm, H. coerulea: 0.07 mm rainfall equivalent), and NP was increasingly depressed at water suprasaturation. In their preferred microhabitat on steep limestone outcrops in alpine regions, endolithic lichens avoid inundation over long time spans, but could perfectly utilize the high air humidity of monthly means between 60 and 80%. Due to light reduction by endolithic growth, both species revealed relatively high photosynthetic light compensation and saturation values, thus avoiding the high light intensities of the alpine habitat. Both lichen species were able to perform 90% of their optimal NP over a wide temperature range and still reached about one-third of their maximum NP rates at 2 °C, demonstrating their capability to cope with the large temperature changes occurring in their habitat.

Phylogenetic Composition of Rocky Mountain Endolithic Microbial Ecosystems

The endolithic environment, the pore space in rocks, is a ubiquitous microbial habitat. Photosynthesis-based endolithic communities inhabit the outer few millimeters to centimeters of rocks exposed to the surface. Such endolithic ecosystems have been proposed as simple, tractable models for understanding basic principles in microbial ecology. In order to test previously conceived hypotheses about endolithic ecosystems, we studied selected endolithic communities in the Rocky Mountain region of the United States with culture-independent molecular methods. Community compositions were determined by determining rRNA gene sequence contents, and communities were compared using statistical phylogenetic methods. The results indicate that endolithic ecosystems are seeded from a select, global metacommunity and form true ecological communities that are among the simplest microbial ecosystems known. Statistical analysis showed that biogeographical characteristics that control community composition, such as rock type, are more complex than predicted. Collectively, results of this study support the idea that patterns of microbial diversity found in endolithic communities are governed by principles similar to those observed in macroecological systems.

Ecology of endolithic lichens colonizing granite in continental Antarctica

In this study, the symbiont cells of several endolithic lichens colonizing granite in continental Antarctica and the relationships they have with the abiotic environment were analyzed in situ, in order to characterize the microecosystems integrating these lichens, from a microecological perspective. Mycobiont and photobiont cells, the majority classified as living by fluorescent vitality testing, were observed distributed through the fissures of the granite. The fact that extracellular polymeric substances were commonly observed close to these cells and the features of these compounds, suggest a certain protective role for these substances against the harsh environmental conditions. Different chemical, physical and biological relationships take place within the endolithic biofilms where the lichens are found, possibly affecting the survival and distribution of these organisms. The alteration of bedrock minerals and synthesis of biominerals in the proximity of these lichens give rise to different chemical microenvironments and suggest their participation in mineral nutrient cycling.

Raman spectroscopic detection of key biomarkers of cyanobacteria and lichen symbiosis in extreme Antarctic habitats: Evaluation for Mars Lander missions

With proposals that micro-miniaturised Raman spectrometers could soon be part of a suite of analytical instrumentation on the surface of Mars, it is critically important to examine the spectral information that could be forthcoming from attempts to determine key molecular biosignatures under the hostile conditions of extra-terrestrial planetary exploration. Current approaches include the analysis of genuine martian geological material in the form of the SNC class meteorites, the formulation of simulated martian regoliths and the examination of putative martian terrestrial analogues; the latter provide the basis of this paper in the form of Antarctic extremophile habitats. In particular, specimens of epilithic, chasmolithic and endolithic lichen and cyanobacterial colonies sampled along a progressively worsening transect towards a “limits of life” situation, beyond which survival of organisms becomes impossible, provide what is arguably the best terrestrial proving-ground for prototype Raman spectrometers for martian exploration. Here, we report the results of experiments on these extant Antarctic extremophile colonies using a range of Raman excitation wavelengths and experimental conditions and also include a compilation of molecular spectral biosignatures, which may be considered as a suitable database for recognition of bioorganic modification of geological strata.

Endolithic growth of two Lecidea lichens in granite from continental Antarctica detected by molecular and microscopy techniques

Through the combined use of molecular and microscopy techniques, the endolithic lichens Lecidea cancriformis and Lecidea sp. were identified, even in the absence of fruiting bodies, and positioned under epilithic lichens. Cells of both algal and fungal symbionts were observed in fissures and cracks of the lithic substrate with no clear heteromerous structure. At the ultrastructural level, the two lichens differed in terms of their algal-fungal relationships. Only one genotype of Trebouxia ITS sequence was identified from specimens of Lecidea sp., Umbilicaria aprina and Buellia frigida from the same zone, which could be mainly determined by low availability of alga in these extreme environments. These lichens showed features typical of both chasmoendolithic and euendolithic microorganisms. Signs of biogeophysical and biogeochemical action on the substrate were detected close to fungal cells. This action seemed to be mainly conditioned by the local physico-chemical features of the substrate. Evidence for the biomobilization of elements by these endolithic lichens was found. L. cancriformis was observed to accumulate substantial amounts of calcium-rich biominerals. The combined approach proposed is useful for mapping the distribution of endolithic lichens and analysing the processes that occur in their microscopic environment.

Morphology and volume of an endolithic Caribbean chiton dwelling

Morphology and volume of an endolithic Caribbean chiton dwelling

Dew moisture regime of endolithic and epilithic lichens inhabiting limestone cobbles and rock outcrops, Negev Highlands, Israel

Summary Endolithic and epilithic lichens proliferate on calcareous cobbles and rock outcrops in the Negev Highlands, Israel. Whereas epilithic lichens predominate in shaded mesohabitats, extensively covering rock outcrops, endolithic lichens proliferate on loose cobbles. Endolithic lichens were thought to predominate in habitats having a poor dew regime. Dew measurements were carried out at habitats of endolithic and epilithic lichens. The measurements took place on loose and partially embedded cobbles with 90–100 % of endolithic lichen cover, and on rock outcrops inhabited by epilithic lichens (75-90 % cover). In addition, independent dew measurements were carried out with the Plate Cloth Method (CPM). A total of 60 days of measurements was performed. Average daily dew amount as obtained by the CPM was 0.20 mm, as compared to 0.18 mm obtained on the loose cobbles, 0.09 mm obtained by the partially embedded cobbles and 0.04–0.08 mm obtained on the bedrock surfaces. The dew amounts obtained on the cobbles were significantly higher than those obtained on the bedrock surfaces (paired t-test, p

An anatomical investigation of calcicolous endolithic lichens from the Trieste karst (NE Italy)

ABSTRACT The anatomy of five endolithic lichens (Acrocordia conoidea, Petractis clausa, Rinodina immersa, Verrucaria baldensis, and V. marmorea) from the Trieste Karst (north-eastern Italy) was thoroughly investigated. Samples already used in previous ecophysiological studies were examined by histological and mineralogical techniques, and by SEM. Biomineralisation products were searched for by X-ray diffractometry, X-ray microdiffractometry, and Fourier Transformed Infrared spectrophotometry. The results confirm that the photobiont layer is located approximately at the same depth in the substratum, although the species occur in habitats with strongly different light regimes; the thallus development is relatively constant within populations of a single species, but differs considerably among species. Several peculiarities of each species were revealed, such as the presence of large clews of hyphae in the inner layer of P. clausa, forming large voids in the substratum, or the development of morphologically different oil-hyphae. Calcium oxalate crystals were not detected. Some terms currently used to describe the anatomy of endolithic lichens are critically discussed, and the new term “lithocortex” and “pseudo-medulla” are introduced.

CO2 exchange of the endolithic lichen Verrucaria baldensis from karst habitats in northern Italy.

CO2 exchange of the endolithic lichen Verrucaria baldensis was measured in the laboratory under different conditions of water content, temperature, light, and CO2 concentration. The species had low CO2 exchange rates (maximum net photosynthesis: c. 0.45 μmol CO2 m-2 s-1; maximum dark respiration: c. 0.3 μmol CO2 m-2 s-1) and a very low light compensation point (7 μmol photons m-2 s-1 at 8°C). The net photosynthesis/respiration quotient reached a maximum at 9-15°C. Photosynthetic activity was affected only after very severe desiccation, when high resaturation respiratory rates were measured. Microclimatic data were recorded under different weather conditions in an abyss of the Trieste Karst (northeast Italy), where the species was particularly abundant. Low photosynthetically active radiation (normally below 40 μmol photons m-2 s-1), very high humidities (over 80%), and low, constant temperatures were measured. Thallus water contents sufficient for CO2 assimilation were often measured in the absence of condensation phenomena.

Fine structural features of rhizomorphs (sensu lato) produced by four species of lichen fungi

Linear mycelial aggregates (rhizomorphs) produced by the squamulose lichens Toninia opuntioides, Squamarina cartilaginea, Lecanora rhizinata , and Acarospora scotica were examined by transmission electron microscopy (TEM). Cytological features typical of lichenized mycobionts were present, including concentric bodies and plasmalemma invaginations. Some septa in rhizomorphs of S. cartilaginea and A. scotica appeared to be multipored. Septal pores were usually plugged by an electron-dense structure. Intrahyphal hyphae were common to abundant in the rhizomorphs of all four species examined. The wall of the invasive hypha was continuous with inner wall layers of the cell of origin. Contacts between adjacent hyphae involved wall dissolution and formation of new wall layers, leading to anastomosis and/or possibly to intrahyphal invasion. Differentiation of an outer layer of collapsed cells in rhizomorphs of Squamarina cartilaginea and of extremely thick-walled cells Lecanora rhizinata was evident, but no anatomical specialization comparable to the ‘vessel hyphae’ of non-lichen linear mycelial organs was observed. Enlarged spheroid or ovoid cells with dense cytoplasm, numerous mitochondria and lipid reserves occurred in short chains in rhizomorphs of Acarospora scotica ; infrequently, similar cells were observed singly in those of Squamarina cartilaginea . These cells were reminiscent in shape of certain types of oil hyphae found in endolithic lichens, although often the lipid content of the enlarged cells was not particularly pronounced.

Experimental strain analysis of Clarens Sandstone colonised by endolithic lichens : D. Wessels, D. Venter, W. Wessels & L. Wessels, Koedoe, 38(2), 1995, pp 35–47

Experimental strain analysis of Clarens Sandstone colonised by endolithic lichens : D. Wessels, D. Venter, W. Wessels & L. Wessels, Koedoe, 38(2), 1995, pp 35–47

Experimental strain analysis of Clarens Sandstone colonised by endolithic lichens

Endolithic lichens occur commonly on Clarens Sandstone in South Africa, where they significantly contribute to the weathering of sandstone by means of mechanical and chemical weathering processes. This preliminary investigation reports on the success- ful use of strain gauges in detecting strain differences between sandstone without epilithic lichens and sandstone colonised by the euendolithic lichen Lecidea aff. sarcogynoides Korb. Mechanical weathering, expressed as strain changes, in Clarens Sandstone was studied during the transition from relatively dry winter to wet summer conditions. Daily weathering of sandstone due to thermal expansion and contraction of colonised and uncolonised sandstone could be shown. Our results show that liquid water in sandstone enhances the mechanical weathering of uncolonised Clarens Sandstone while water in the gaseous phase enhances mechanical weathering of sandstone by euendolithic lichens.

Gas exchange rates and chlorophyll content of epi- and endolithic lichens from the Trieste Karst (NE Italy).

The photosynthetic activity of calcicolous endo- and epilithic lichens from the Trieste Karst area (NE Italy) was investigated. The data consist of: (a) gas exchange rates of Acrocordia conoidea, Petractis clausa, Rinodina immersa (endolithic), and Aspicilia calcarea (epilithic), recorded at different combinations of temperature, water content and radiation flux values, (b) chlorophyll content values of nine species, and (c)δ13 C values measured in 24 lichen species with different growth-forms. The results show that: (1) the maximum photosynthetic rates of endolithic lichens are rather small, ranging between 0·2 and 1·5μmol CO2 m-2 h-1 at optimal conditions; (2) the relation between thallus water content and photosynthesis differs from that of foliose and fruticose lichens; the optimum water content of endolithic lichens is particularly small, when expressed in g H2 O cm-2 ; (3) the algae of endolithic lichens, which belong to different systematic groups, are light-saturated at a small radiation flux; (4) chlorophyll contents of endolithic lichens are rather large, being similar to those of some parmelioid lichens. The ecological implications of the endolithic growth-form are briefly discussed. Endolithic lichens should be regarded as slow-growing, stress-tolerant organisms, which are rather similar in their physiology to epilithic crustose lichens; they have a high resistance to CO2 diffusion, saturation being reached only at a very large CO2 concentration.

Ecophysiology of calcicolous endolithic lichens: progress and problems

Abstract The biology of calcicolous endolithic lichens is far from being well-known. In this paper the results of a multidisciplinar research are presented. The study is based on laboratory and field data, and is divided in four parts: (1) anatomical investigation of the species; (2) characterization of gas exchange rates of selected epi- and endolithic lichens; response curves were obtained in dependence to the main abiotic factors (thallus water content, light, CO2 concentration, temperature); (3) characterization of chemical-physical parameters of the substratum (porosity, capillarity, etc.); (4) field measurements of microclimatic parameters in the habitat of each species, and quantification of thallus hydration in situ during selected days at different weather conditions. Six species, five of them endolithic (Acrocordia conoidea, Petractis clausa, Rinodina immersa, Verrucaria marmorea and Verrucaria sp.) and one epilithic (Aspicilia radiosa) were investigated in the VG 46 abyss near Gropada (Trieste ...

Photosynthetic performance of rock-colonising lichens in the Mountain Zebra National Park, South Africa

The photosynthetic behaviour of endolithic andepilithic lichens characteristic of sedimentary and volcanic rock was investigated in situ in the Mountain Zebra National Park, South Africa. The park forms part of an inland semi-desert known as the Karoo, in the Cape Province. Temperatures within Balfour sandstone were monitored, the results showing that during the early morning, temperatures within the sandstone were nearly 5@C lower than ambient air temperatures. This may enhance the frequency of water condensing on the sandstone, which may be particularly important for the endoliths Leciclea aff. sarcogynoides and Sarcogyne cf. austroafricana. Maximum photosynthetic rates of the investigated species were found at temperatures between 20@C and 30@C, far higher than the recorded optimum temperatures for lichens from temperate and desert regions. Parmelia chlorea was the most productive species. Compared to the other epiliths, Peltula capensis was found to be a moderately productive species. The photosynthetic gain of Leciclea aff. sarcogynoides and Sarcogyne cf. austro-africana was low, but the photosynthetic gain of these two species still exceeded that of Acarospora sp.

Responses in Growth, Reproduction and Life Span to Reduced Competition Pressure in the Land Snail Balea perversa

Intraspecific interactions early in an individual's life may lead to reduced reproduction once maturity is attained. Possibly, this could be compensated by increased or prolonged reproduction later in life if competition is relaxed (i.e. after a sudden decrease in population density as the result of a catastrophic event). We tested this compensation hypothesis in the ovoviviparous, self-fertilizing land snail Balea perversa (L.). Juvenile snails were kept for 450 d at different densities on their natural substrate and food (pieces of limestone providing epi- and endolithic lichens). After this period of intraspecific competition, individuals were kept singly under conditions of high food supply for the rest of their life (126-484 d; period of relaxed competition)

The postfire recovery of rock-inhabiting algae, microfungi, and lichens

Despite numerous investigations on the re-establishment of epiphytic cryptogams, especially lichens, after forest fires, very little is known about the recolonization of burnt rocks by lithobiontic microorganisms after fire in the Mediterranean region. Reported herein are the results of a combined field observation and scanning electron microscopy study focusing on the connection between the microrelief of the rocks that was shaped during prefire periods and the recolonization of pioneer lithobiontic microorganisms after the fire. Scanning electron microscopy revealed that the burnt rock surfaces exhibit 10 kinds of weathering elements that include 9 kinds of cryptogamic imprints corroded by saxicolous (rock-inhabiting) unicellular green algae, free-living microfungi, and fruiting bodies or microgrooves of endolithic lichens during prefire periods. The total volume of several selected structural weathering elements formed by lithobiontic microorganisms during the prefire period was estimated relative to the possible contribution of these lithobionts to local pedogenesis. Considering that the specific weight of chalk is 2.6 g/cm3, the estimated amount of the rock material removed by small pits with a diameter of 0.01 mm formed by unicellular green algae during the prefire period can reach 3.06 kg/ha mountain area with 10% rock coverage, while the estimated amount of chalk rock material removed by pinhead holes with a diameter of 0.8 mm formed by fruiting bodies of endolithic lichens can reach 174 kg/ha with the same rock coverage. Water-holding capacity of empty pinhead holes and small pits on the rock surface in burnt areas was also estimated, and it is suggested that the water-holding capacity of empty small pits (d = 0.01 mm) formed by unicellular green algae on rock surface per hectare mountain area with 10% rock coverage can reach 1.18 L, whereas in case of pinhead holes (d = 0.8 mm) formed by fruiting bodies of endolithic lichens the water-holding capacity can reach 66.9 L/ha with the same rock coverage. Scanning electron microscopy revealed the presence of three different kinds of unicellular green algae, one free-living microfungus, two different species of endolithic lichens, two epilithic lichen species, and great numbers of lichen ascospores, fungal spores, and hyphae established postfire in pinhead holes and small pits produced by former microlithobionts inhabiting rocks during prefire periods. These microorganisms and diaspores were also present in ruts, shallow rock depressions, and microcrevices produced by abiotic factors. Key words: lithobiontic microorganisms, wildfire, algae, microfungi, lichens.

Erosion of Biogenically Weathered Clarens Sandstone by Lichenophagous Bagworm Larvae (Lepidoptera; Pyschidae)

AbstractLichenophagous larvae of a bagworm moth species, associated with endolithic lichens occur in the Golden Gate Highlands National Park, South Africa. Endolithic lichens weather Clarens sandstone in the park by dissolving the cementing material of the sandstone. Bagworm larvae use such loosened quartz crystals to construct the bags in which they live. By erosion of the weathered sandstone, the bagworm larvae contribute to pedogenesis in the park at an estimated rate of 4.4 kilograms per hectare per year. In addition, bagworm larvae utilize endolithic lichens as a food source and contribute to dispersal of the lichens. The larvae further contribute an estimated 200 g of organic matter per hectare per year to the park and partake in the cycling of elements in the micro-ecosystem.

Fertilization of the desert soil by rock-eating snails

PLANT productivity in deserts can be nitrogen-limited. Nitrogen inputs are often low, soil nitrogen pools small, and losses from runoff, erosion, volatilization and denitrification, can be high1–6. We have now found an unusual, important source of soil nitrogen in the Central Negev Highlands of Israel, a limestone rock desert with patches of soil (Fig. 1). Snails feed on endolithic lichens that grow within the rock, ingesting both rock and lichens7,8, and depositing their faeces on the soil under the rocks. Snails transfer between 22–27 mg nitrogen per m2 per year to soil, which constitutes about 11% of total soil nitrogen inputs, at least 18% of net soil inputs, and a minimum of 27% of the nitrogen annually accumulated by endolithic lichens from dust. The substantial contribution of snails to the nitrogen cycle is probably important for higher plant production.

Ichnological study of shallow marine endolithic sponges from the Italian coast

Living boring sponges belonging to eight species of the genera Siphonodictyon , Cliona and Cliothosa , were collected from the limestone seafloor of the Apulian coast. Samples were taken in zero to -20 m water depth. Spicule preparations from the sponges, and epoxy casts of the borings, facilitated a comparison of the animal and its work. The borings were analyzed ichnotaxonomically and attributed to 11 ichnospecies of Entobia . Direct correlation between biospecies and ichnospecies was not found in all cases. Several ichnospecies are new, and some of these are named using Pleistocene material. The new ichnospecies are Entobia gigante a, E. magma and E. parva .