Fungal Sheath Research Articles

Ультраструктура эктомикориз лесообразующих хвойных пород в условиях подзоны средней тайги

Mycorrhiza are symbiotic formations of fungus and roots and are the main organs of nutrient uptake by land plants. The formation of ectomycorrhizae allows trees to dominate the vegetation cover of the boreal zone. Pinus sylvestris L., Picea obovata Ledeb. и Abies sibirica Ledeb. are forest-forming conifers of the Komi Republic. Transmission electron microscopy shows that the fungal sheath of mycorrhiza is most developed in A. sibirica. The Hartig net in all studied trees extends deep into the primary cortex to the endodermis. Glycogen accumulates in the cytoplasm and polyphosphate-containing granules (volutin) in the vacuoles of young fungal cells. Starch accumulates in the cells of primary cortex and central cylinder of young ectomycorrhizae. Reserve substances disappear in the sheath and the Hartig net as the mycorrhiza ages, and starch can remain in the central cylinder. A stable presence of reserve substances was noted at the beginning and in the middle of the growing season. There is an active growth of sucking roots and the formation of ectomycorrhizae during this period in the middle taiga subzone. The occurrence of glycogen and polyphosphate-containing granules in fungal cells is reduced in the autumn period. This is due to a decrease in the intensity of growth processes and the prevalence of physiologically inactive mycorrhizal endings. The starch decrease in the amyloplasts of the primary cortex cells and the central cylinder of ectomycorrhizae is associated with a seasonal decrease in its content in all tree organs, preparation of the plant for the season with low temperatures.

Diversity analysis of antagonistic microbes against bacterial leaf and fungal sheath blight diseases of rice

BackgroundBiocontrol is an effective strategy in the integrated management of plant diseases, now more as a necessity than choice, in the present era of environmental and health awareness. Microbial diversity is a wonder by nature that inspires to explore and accordingly, the diversity analysis of the isolated microbes revealed their morphological and molecular differences. The DNA provides a common platform to store the microbial information in the form of databases in public domain that can be used by anyone from anywhere.ResultsExploration for native microbes in the present study resulted in isolation of different isolates of Trichoderma and Bacillus. The microbes were identified using morphological traits and molecular markers and the key conserved 18S and 16S gene sequences submitted with the appropriate repositories. Nucleotide analysis indicated a close phylogenetic relationship between BIK 2 and BIK 3 (Bacillus isolates) and within all the 5 Trichoderma isolates. The percent disease reduction of Rhizoctonia solani and Xanthomonas oryzae pv. oryzae (Xoo) was more in plants treated with consortia of the Trichoderma (61.13%) and Bacillus (53.59%) isolates, respectively. Screening of plant growth promotion activities, percentage increase in root (41.00%) and shoot length (44.77%) were found to be maximum in Trichoderma consortia treated plants.ConclusionsThree Bacillus and one Trichoderma strains, viz., B. velezensis, B. subtilis and B. paralicheniformis and Trichoderma asperellum, were identified and found to be effective against R. solani and Xoo pathogens of rice. In vitro and in vivo studies indicated that TAIK1 and BIK3 were found to be the most potential isolates among others isolated. Ability to improve plant growth was more pronounced by consortia of microbes.

Disentangling the role of ectomycorrhizal fungi in plant nutrient acquisition along a Zn gradient using X-ray imaging

Zinc (Zn) is a plant essential micronutrient involved in a wide range of cellular processes. Ectomycorrhizal fungi (EMF) are known to play a critical role in regulating plant Zn status. However, how EMF control uptake and translocation of Zn and other nutrients in plant roots under different Zn conditions is not well known. Using X-ray fluorescence imaging, we found the EMF species Suillus luteus increased pine root Zn acquisition under low Zn concentrations and reduced its accumulation under higher Zn levels. By contrast, non-mycorrhizal pine roots exposed to high Zn indiscriminately take up and translocate Zn to root tissues, leading to Zn stress. Regardless of S. luteus inoculation, the absorption pattern of Ca and Cu was similar to Zn. Compared to Ca and Cu, effects of S. luteus on Fe acquisition were more marked, leading to a negative association between Zn addition and Fe concentration within EMF roots. Besides, higher nutrient accumulation in the fungal sheath, compared to hyphae inhabiting between intercellular space of cortex cells, implies the fungal sheath serves as a barrier to regulate nutrient transportation into fungal Hartig net. Our results demonstrate the crucial roles EMF play in plant nutrient uptake and how fungal partners ameliorate soil chemical conditions either by increasing or decreasing element uptake.

Preparation of intracellular proteins from a white-rot fungus surrounded by polysaccharide sheath and optimization of their two-dimensional electrophoresis for proteomic studies

The functions and properties of fungal sheath, an extracellular polysaccharide produced by many white-rot fungi, have been studied. However, the strong adherence of the sheath to fungal hyphae had been a major impediment in preparing intracellular proteins from the fungi and analyzing their cellular responses. To overcome this issue, we developed a rapid and easy method to remove the polysaccharide sheath using a selective lignin degrader, Ceriporiopsis subvermispora, which produces large sheath amounts in the presence of a lignin-derived aromatic compound. Using this approach, we achieved thorough removal of sheath and cell disruption using beads and a solution with a high protein-solubilizing power, which enabled the efficient extraction of intracellular proteins from C. subvermispora surrounded by sheath. In addition, for proteomic analysis, we investigated whether these extracted proteins were compatible with two-dimensional electrophoresis. By efficiently concentrating on protein solubilization in the first dimension and using a stacking gel in the second dimension, we successfully obtained a high-resolution proteome map of C. subvermispora. We also used the same proteins for fluorescence two-dimensional difference gel electrophoresis to obtain the quantitative protein expression profiles. These steps demonstrated that two-dimensional electrophoresis-based proteomics can be used to clarify the composition of intracellular proteins from sheath-producing white-rot fungi.

ANATOMIC-MORPHOLOGICAL INDICATORS MYCORRHIZA SEEDLINGS QUERCUS ROBUR L. IN CONDITIONS OF RADIOACTIVE CONTAMINATION

Research of anatomical and morphological indicators of mycorrhizal seedlings Quercus robur L. was conducted on 8 test areas both at relatively pure plantations in the territory of training-experimental forestry of the Bryansk region, and in conditions of chronic pollution with radionuclides in the Krasnogorsk forestry. All mycorrizal we investigated releted to ectomycorrhiza (or to ectotrophic mycorrhiza of trees and bushes) and have typical for this type of mycorrhiza anatomical structure. Reporded plektenhimatous (subtype B, C, D, A), pseudoparenchymatous (subtype F, H, I), double (subtype N, P) and unstructured (subtype S) types of mycorrhiza. Mycorrhizae with plektenhimatous and pseudoparenchymatous types of fungal sheath recorded on all plots, that allowed us to trace the changes in anatomical and morphological indicators at different levels of pollution. With increasing exposure rate of 120 to 600 mR / h on the surface of the soil some anatomical parameters of mycorrhiza, are statistically authentically increase, peaking at exposure rate = 500 ... 600 mR / h. A further increase exposure rate (700 ... 1000 mR / h) leads to their reduction. However, fungal sheath thickness, the thickness of parenchyma cortex, and the total thickness of Quercus robur L. mycorrhiza at this exposure rate level are significantly higher than exposure rate control. These data can be explained by the stimulating effect of exposure rate = 120 ... 600 mR / h at the end of the mycorrhizal root of Quercus robur L. or by mycorrhiza adaptation to adverse radioactivity effect. The results of our research can be used for determine the expouse rate level which is, optimal for reforestation works in the radioactively contaminated areas.

Structural characterization of highly branched glucan sheath from Ceriporiopsis subvermispora

Wood rotting basidiomycetes produce extracellular mucilaginous sheaths interfacing fungal hyphae and plant biomass. While the versatility of these fungal sheaths has been addressed, sheaths generated by selective white-rot fungi remain poorly understood. To fill this gap, the sheath produced by the basidiomycete Ceriporiopsis subvermispora, which degrades lignin while inflicting limited cellulose damage, was analyzed in this study. Fluorescence and transmission electron microscopy revealed that the sheath formed three days after inoculation into a beech wood slice on an agar plate and was embedded at the interface between fungal hyphae and wood cell walls. The sheath’s chemical structure was evaluated from fungus cultures in a liquid medium containing [U-13C6]-d-glucose and beech wood slices. Compositional analysis, methylation analysis, and 13C NMR demonstrated that the sheath mainly consisted of a comb-like β-1,6-glucopyranose residue-branched β-1,3-glucan, which is advantageous to retain water and extracellular secondary metabolites.

First detection of Endogone ectomycorrhizas in natural oak forests.

The order Endogonales in Mucoromycotina, an early divergent lineage of fungi, includes ectomycorrhizal (EM) fungi. This order is therefore considered a key taxon for elucidation of the evolution of EM associations. Recent studies have revealed high diversity of EM lineages of Basidiomycota and Ascomycota; however, EM associations of Endogonales and its relatives remain largely unknown. In this study, EM root tips with a unique fungal sheath, with aseptate and highly branched hyphae of variable widths, were identified in Quercus acutissima and Quercus crispula forests in the temperate zone of Japan. The mycobionts were confirmed as Endogone sp., which were placed as a sister clade of Endogone pisiformis, based on phylogenetic analyses of the small and large subunits of the nuclear ribosomal RNA and elongation factor-1α genes. This is the first report of EM of Endogone in natural forests of the Northern Hemisphere and the first finding on Quercus.

A fungal conserved gene from the basidiomycete Hebeloma cylindrosporum is essential for efficient ectomycorrhiza formation.

We used Agrobacterium-mediated insertional mutagenesis to identify genes in the ectomycorrhizal fungus Hebeloma cylindrosporum that are essential for efficient mycorrhiza formation. One of the mutants presented a dramatically reduced ability to form ectomycorrhizas when grown in the presence of Pinus pinaster. It failed to form mycorrhizas in the presence of glucose at 0.5 g liter(-1), a condition favorable for mycorrhiza formation by the wild-type strain. However, it formed few mycorrhizas when glucose was replaced by fructose or when glucose concentration was increased to 1 g liter(-1). Scanning electron microscopy examination of these mycorrhizas revealed that this mutant was unable to differentiate true fungal sheath and Hartig net. Molecular analyses showed that the single-copy disrupting T-DNA was integrated 6,884 bp downstream from the start codon, of an open reading frame potentially encoding a 3,096-amino-acid-long protein. This gene, which we named HcMycE1, has orthologs in numerous fungi as well as different other eukaryotic microorganisms. RNAi inactivation of HcMycE1 in the wild-type strain also led to a mycorrhizal defect, demonstrating that the nonmycorrhizal phenotype of the mutant was due to mutagenic T-DNA integration in HcMycE1. In the wild-type strain colonizing P. pinaster roots, HcMycE1 was transiently upregulated before symbiotic structure differentiation. Together with the inability of the mutant to differentiate these structures, this suggests that HcMycE1 plays a crucial role upstream of the fungal sheath and Hartig net differentiation. This study provides the first characterization of a fungal mutant altered in mycorrhizal ability.

Ectomycorrhizas in vitro between Tricholoma matsutake, a basidiomycete that associates with Pinaceae, and Betula platyphylla var. japonica, an early-successional birch species, in cool-temperate forests.

Tricholoma matsutake is an ectomycorrhizal basidiomycete that associates with Pinaceae in the Northern Hemisphere and produces prized "matsutake" mushrooms. We questioned whether the symbiont could associate with a birch that is an early-successional species in boreal, cool-temperate, or subalpine forests. In the present study, we demonstrated that T. matsutake can form typical ectomycorrhizas with Betula platyphylla var. japonica; the associations included a Hartig net and a thin but distinct fungal sheath, as well as the rhizospheric mycelial aggregate "shiro" that is required for fruiting in nature. The in vitro shiro also emitted a characteristic aroma. This is the first report of an ectomycorrhizal formation between T. matsutake and a deciduous broad-leaved tree in the boreal or cool-temperate zones that T. matsutake naturally inhabits.

OsNPR1 GENE EXPRESSION IN RESPONSE TO SALYSILIC ACID IN RICE

NPR1 gene plays an important role in the activation of systemic acquired resistance (SAR). This research was conducted to examine the expression profiles of OsNPR1 gene in four rice varieties: Pongsu Seribu, MR219, MRQ74 and CO39 in response to treatment with salicylic acid (SA). All four varieties vary in their level of resistance to fungal sheath blight disease while Pongsu Seribu showed the highest tolerance. SA treatment did not result in an increase in the level of expression in all varieties except for CO39 which is highly susceptible to blast disease and OsNPR1 expressed in untreated CO39 was lower than the other three varieties. The overall results of this study show that SA did not result in increased expression of OsNPR1 gene in all varieties. We therefore may conclude that exogenous SA does not induce NPR1 gene in rice due to the higher endogenous levels of SA in rice. In addition SAR in rice may be controlled by non SA mediated pathways or combinatorial pathways.Â

Co-expression of RCH10 and AGLU1 confers rice resistance to fungal sheath blight Rhizoctonia solani and blast Magnorpathe oryzae and reveals impact on seed germination

Rice sheath blight and blast caused by Rhizoctonia solani Kühn and Magnorpathe oryzae respectively, are the two most destructive fungal diseases in rice. With no genetic natural traits conferring resistance to sheath blight, transgenic manipulation provides an obvious approach. In this study, the rice basic chitinase gene (RCH10) and the alfalfa β-1,3-glucanase gene (AGLU1) were tandemly inserted into transformation vector pBI101 under the control of 35S promoter with its enhancer sequence to generate a double-defense gene expression cassette pZ100. The pZ100 cassette was transformed into rice (cv. Taipei 309) by Agrobacterium-mediated transformation. More than 160 independent transformants were obtained and confirmed by PCR. Northern analysis of inheritable progenies revealed similar levels of both RCH10 and AGLU1 transcripts in the same individuals. Disease resistance to both sheath blight and blast was challenged in open field inoculation. Immunogold detection revealed that RCH10 and AGLU1 proteins were initially located mainly in the chloroplasts and were delivered to the vacuole and cell wall upon infection, suggesting that these subcellular compartments act as the gathering and execution site for these anti-fungal proteins. We also observed that transgenic seeds display lower germination rate and seedling vigor, indicating that defense enhancement might be achieved at the expense of development.

Insights into root growth, function, and mycorrhizal abundance from chemical and isotopic data across root orders

Detailed analyses of root chemistry by branching order may provide insights into root function, root lifespan and the abundance of root-associated mycorrhizal fungi in forest ecosystems. We examined the nitrogen and carbon stable isotopes (δ15N and δ13C) and concentration (%N and %C) in the fine roots of an arbuscular mycorrhizal tree, Fraxinus mandshurica, and an ectomycorrhizal tree, Larix gmelinii, over depth, time, and across five root branching orders. Larix δ15N increased by 2.3 ‰ from 4th order to 1st order roots, reflecting the increased presence of 15N-enriched ECM fungi on the lower root orders. In contrast, arbuscular mycorrhizal Fraxinus only increased by 0.7 ‰ from 4th order to 1st order roots, reflecting the smaller 15N enrichment and lower fungal mass on arbuscular mycorrhizal fine roots. Isotopic and anatomical mass balance calculations indicate that first, second, and third order roots in ectomycorrhizal Larix averaged 36 %, 23 %, and 8 % fungal tissue by mass, respectively. Using literature values of root production by root branching order, we estimate that about 25 % of fine root production in ECM species like Larix is actually of fungal sheaths. In contrast to %N, %C, and δ15N, δ13C changed minimally across depth, time, and branching order. The homogeneity of δ13C suggests root tissues are constructed from a large well-mixed reservoir of carbon, although compound specific δ13C data is needed to fully interpret these patterns. The measurements developed here are an important step towards explicitly including mycorrhizal production in forest ecosystem carbon budgets.

Modeling the evolutionary rise of ectomycorrhiza on sub-surface weathering environments and the geochemical carbon cycle

For the past two decades, the spread of angiosperm plants in the Cretaceous and Paleogene has been thought to have enhanced silicate weathering fluxes of Ca and Mg to the oceans, thereby drawing down atmospheric CO~2~ and ultimately sequestering it in marine carbonate sediments. However, the rise of angiosperm trees in the Cretaceous was coincident with the evolution of ectomycorrhizal fungal associations in angiosperm and gymnosperm trees that have increasingly supplanted trees with the ancestral arbuscular-mycorrhizal associations. This represents the most profound alteration in root functioning to occur in plant evolutionary history, with far-reaching implications for weathering and soil biogeochemistry because the fine roots are enveloped with a fungal sheath. Ectomycorrhizal fungi provide the main nutrient and water-absorbing interface with soil, and the pathway through which organic acids and protons are actively secreted at the scale of individual mineral grains. Here, we test the hypothesis that the rise of ectomycorrhizal trees was a major contributor to the drawdown of atmospheric CO~2~ over the past 120 Ma through enhanced silicate weathering. We developed a process-based soil chemistry model incorporating the effects of plants with ancestral arbuscular mycorrhizas, and more recently evolved ectomycorrhizas on soil chemistry via its effects on the biological proton cycle, and integrated it into a leading model of the long-term carbon cycle (GEOCARBSULF). Our mechanistic, process-based modeling reveals that the rise of ectomycorrhizal trees can explain the CO~2~ drawdown previously attributed empirically to the spread of angiosperms. We suggest, therefore, that the evolutionary rise of ectomycorrhizas represents an important driving force of the long-term carbon cycle by enhancing chemical weathering and draw-down of atmospheric CO~2~ into marine carbonates.

Nickel-tolerant ectomycorrhizal Pisolithus albus ultramafic ecotype isolated from nickel mines in New Caledonia strongly enhance growth of the host plant Eucalyptus globulus at toxic nickel concentrations

Ectomycorrhizal (ECM) Pisolithus albus (Cooke & Massee), belonging to the ultramafic ecotype isolated in nickel-rich serpentine soils from New Caledonia (a tropical hotspot of biodiversity) and showing in vitro adaptive nickel tolerance, were inoculated to Eucalyptus globulus Labill used as a Myrtaceae plant-host model to study ectomycorrhizal symbiosis. Plants were then exposed to a nickel (Ni) dose-response experiment with increased Ni treatments up to 60 mgkg( - )(1) soil as extractable Ni content in serpentine soils. Results showed that plants inoculated with ultramafic ECM P. albus were able to tolerate high and toxic concentrations of Ni (up to 60 μgg( - )(1)) while uninoculated controls were not. At the highest Ni concentration tested, root growth was more than 20-fold higher and shoot growth more than 30-fold higher in ECM plants compared with control plants. The improved growth in ECM plants was associated with a 2.4-fold reduction in root Ni concentration but a massive 60-fold reduction in transfer of Ni from root to shoots. In vitro, P. albus strains could withstand high Ni concentrations but accumulated very little Ni in its tissue. The lower Ni uptake by mycorrhizal plants could not be explained by increased release of metal-complexing chelates since these were 5- to 12-fold lower in mycorrhizal plants at high Ni concentrations. It is proposed that the fungal sheath covering the plant roots acts as an effective barrier to limit transfer of Ni from soil into the root tissue. The degree of tolerance conferred by the ultramafic P. albus isolates to growth of the host tree species is considerably greater than previously reported for other ECM. The primary mechanisms underlying this improved growth were identified as reduced Ni uptake into the roots and markedly reduced transfer from root to shoot in mycorrhizal plants. The fact that these positive responses were observed at Ni concentrations commonly observed in serpentinic soils suggests that ultramafic ecotypes of P. albus could play an important role in the adaptation of tree species to soils containing high concentrations of heavy metals and aid in strategies for ecological restoration.

Slow decomposition of lower order roots: a key mechanism of root carbon and nutrient retention in the soil

Among tree fine roots, the distal small-diameter lateral branches comprising first- and second-order roots lack secondary (wood) development. Therefore, these roots are expected to decompose more rapidly than higher order woody roots. But this prediction has not been tested and may not be correct. Current evidence suggests that lower order roots may decompose more slowly than higher order roots in tree species associated with ectomycorrhizal (EM) fungi because they are preferentially colonized by fungi and encased by a fungal sheath rich in chitin (a recalcitrant compound). In trees associated with arbuscular mycorrhizal (AM) fungi, lower order roots do not form fungal sheaths, but they may have poorer C quality, e.g. lower concentrations of soluble carbohydrates and higher concentrations of acid-insolubles than higher order roots, thus may decompose more slowly. In addition, litter with high concentrations of acid insolubles decomposes more slowly under higher N concentrations (such as lower order roots). Therefore, we propose that in both AM and EM trees, lower order roots decompose more slowly than higher order roots due to the combination of poor C quality and high N concentrations. To test this hypothesis, we examined decomposition of the first six root orders in Fraxinus mandshurica (an AM species) and Larix gmelinii (an EM species) using litterbag method in northeastern China. We found that lower order roots of both species decomposed more slowly than higher order roots, and this pattern appears to be associated mainly with initial C quality and N concentrations. Because these lower order roots have short life spans and thus dominate root mortality, their slow decomposition implies that a substantial fraction of the stable soil organic matter pool is derived from these lower order roots, at least in the two species we studied.

Fungal content of ectomycorrhizal tips: comparison among 13 tree species

To better understand soil carbon cycling in forest ecosystems, we studied the proportion of fungal sheath area (FSA) in the cross-sectional ectomycorrhizal area in 13 tree species. Ectomycorrhizal samples were collected from subalpine and temperate forests in Japan. The FSA values were in the range of 12% to 56% across all tree species, tree ages, and fungal species. In Abies firma and Quercus serrata, the FSA values were larger in mature trees than in seedlings, whereas no such differences were found in Pinus densiflora and Fagus crenata. In broad-leaved trees, because the plant tissue radii lay within a narrow range, the FSA was affected mainly by the fungal sheath thickness. In conifers, however, the plant tissue radii varied widely among genera, so the FSA was affected by both the plant tissue radius and the fungal sheath thickness. Our findings suggest that the fungal content of ectomycorrhizal tips differs among tree species and fungal species, so that both parameters must be considered in studies of forest carbon cycling. The estimates revealed that data gathering in each type of forest leads to more accurate estimates of the biomass of fungi in ectomycorrhizal tips.

Trehalose synthesis in ectomycorrhizas – a driving force of carbon gain for fungi?

Trehalose synthesis in ectomycorrhizas – a driving force of carbon gain for fungi?

Increased trehalose biosynthesis in Hartig net hyphae of ectomycorrhizas

To obtain photoassimilates in ectomycorrhizal symbiosis, the fungus has to create a strong sink, for example, by conversion of plant-derived hexoses into fungus-specific compounds. Trehalose is present in large quantities in Amanita muscaria and may thus constitute an important carbon sink. In Amanita muscaria-poplar (Populus tremula x tremuloides) ectomycorrhizas, the transcript abundances of genes encoding key enzymes of fungal trehalose biosynthesis, namely trehalose-6-phosphate synthase (TPS), trehalose-6-phosphate phosphatase (TPP) and trehalose phosphorylase (TP), were increased. When mycorrhizas were separated into mantle and Hartig net, TPS, TPP and TP expression was specifically enhanced in Hartig net hyphae. Compared with the extraradical mycelium, TPS and TPP expression was only slightly increased in the fungal sheath, while the increase in the expression of TP was more pronounced. TPS enzyme activity was also elevated in Hartig net hyphae, displaying a direct correlation between transcript abundance and turnover rate. In accordance with enhanced gene expression and TPS activity, trehalose content was 2.7 times higher in the Hartig net. The enhanced trehalose biosynthesis at the plant-fungus interface indicates that trehalose is a relevant carbohydrate sink in symbiosis. As sugar and nitrogen supply affected gene expression only slightly, the strongly increased expression of the investigated genes in mycorrhizas is presumably developmentally regulated.

Fungal content of ectomycorrhizal tips: comparison among 13 tree species

To better understand soil carbon cycling in forest ecosystems, we studied the proportion of fungal sheath area (FSA) in the cross-sectional ectomycorrhizal area in 13 tree species. Ectomycorrhizal samples were collected from subalpine and temperate forests in Japan. The FSA values were in the range of 12% to 56% across all tree species, tree ages, and fungal species. In Abies firma and Quercus serrata, the FSA values were larger in mature trees than in seedlings, whereas no such differences were found in Pinus densiflora and Fagus crenata. In broad-leaved trees, because the plant tissue radii lay within a narrow range, the FSA was affected mainly by the fungal sheath thickness. In conifers, however, the plant tissue radii varied widely among genera, so the FSA was affected by both the plant tissue radius and the fungal sheath thickness. Our findings suggest that the fungal content of ectomycorrhizal tips differs among tree species and fungal species, so that both parameters must be considered in studies of forest carbon cycling. The estimates revealed that data gathering in each type of forest leads to more accurate estimates of the biomass of fungi in ectomycorrhizal tips.

Origin of pedogenic needle-fiber calcite revealed by micromorphology and stable isotope composition—a case study of a Quaternary paleosol from Hungary

Pedogenic needle-fiber calcite was studied regarding its morphology, texture and stable isotope composition from the paleosol of the Quaternary Várhegy travertine (Budapest, Hungary). The needle-fiber calcite is composed of 40–200 μm long monocrystals. Smooth rods as well as serrated-edged crystals with calcite overgrowths were identified by SEM. Needles have several textural varieties: randomly distributed crystals in vugs and pores with calcite hypocoatings, bundles of subparallel crystals forming coatings around grains and alveolar structure with bridging needles in vugs. The morphological study of needle-fiber calcite suggests that needles are calcified fungal sheaths and produced by fungal biomineralization, a common process in recent and fossil soils and calcretes. The stable isotope composition of needle-fiber calcite (average: δ 18 O = - 7.1 ‰ and δ 13 C = - 7.3 ‰ vs. V-PDB) indicates significant incorporation of organically derived CO 2 and probably biological influence on needle genesis. Dissolved host rock travertine and/or atmospheric CO 2 could also contribute some carbon to the acicular calcite.