Cord-forming Fungi Research Articles

Spatial resource arrangement influences both network structures and activity of fungal mycelia: A form of pattern recognition?

The present study investigated the behavior and wood decay ability of mycelial network of Phanerochaete velutina, a cord-forming fungus, on multiple wood blocks. We placed well-colonized wood blocks in two spatial arrangements (Circle and Cross) on a soil plate and compared the development of the mycelial network and wood decay over 116 days. In the Circle arrangement, the degree of connection (number of connected cords) of the blocks ranged from 0 to 8, with no significant differences observed across positions. However, in the Cross arrangement, the outer blocks exhibited a greater degree of connection than the inner blocks. The mass loss of the wood block was positively associated with the degree of connection and was significantly smaller in the Cross than in the Circle arrangement. These findings suggest that fungal mycelium can “recognize” the difference in the spatial arrangement of wood blocks as part of their wood decay activity.

Impact of Parvodontia austrosinensis on Lansium domesticum in Northern Thailand

ABSTRACT Lansium domesticum (Osbeck) Sahni and Bennet (Longkong) is a highly important and valuable fruit crop in Thailand. The mycobiota of L. domesticum has been understudied. In our survey of fungal diseases affecting fruit crops in Thailand, we observed unusual mycelial development in organically cultivated L. domesticum in Uttaradit Province. The mycelia initially appear as cords on the upper half of the young trees and spread towards the crown. However, the adverse growth of mycelial cords shows invasive development over the tree and is associated with fruits showing soft rot. The trees covered with mycelia cords eventually decay and die, and the effect was observed to be irreversible. Taxonomic and phylogenetic studies identified the mycelial cord-forming fungal species as Parvodontia austrosinensis. Pathogenicity studies on detached leaves and fruit bunches showed field symptoms confirming P. austrosinensis as the mycelial cord-forming fungi on L. domesticum and pathogen associated with fruit soft rot. This study presents the first geographic and host record of P. austrosinensis in Thailand on L. domesticum. Moreover, it is the first report of P. austrosinensis associated with fruit soft rot and plantation decay. Furthermore, this study is the first report on the disease potential of Cystostereaceae, which was previously known for a saprobic lifestyle.

Diversity and Phylogeny of Novel Cord-Forming Fungi from Borneo.

Cord-forming (CF) fungi are found worldwide; however, tropical CF fungi are poorly documented. They play an essential role in forest ecosystems by interconnecting nutrient resources and aiding in the decomposition of plant matter and woody litter. CF fungi samples were collected from two forest conservation sites in the Sabah region of Malaysian Borneo. Sequencing and phylogenetic analysis of the ribosomal rRNA gene array 18S to 28S region from cords collected placed all of the collected specimens in Agaricomycetes (Basidiomycetes), specifically within the orders Trechisporales, Phallales, Hymenochaetales, Polyporales, and Agaricales. Comparison of the cord-derived sequences against GenBank and UNITE sequence databases, as well as phylogenetic analyses, revealed they were all novel sequences types. Many of these novel lineages were found to be closely related to other basidiomycetes commonly found in tropical forests, suggesting a large undiscovered tropical fungal diversity in Borneo that has been detected independently of sampling fruiting bodies. We show how these sequence types relate to the morphologies of the cords from which they were sampled. We also highlight how rapid, small-scale sampling can be a useful tool as an easy and relatively unbiased way of collecting data on cord-forming fungi in difficult-to-access, complex forest environments, independently of locating and sampling sporophores.

Effects of isopod population density on woodland decomposer microbial community function

Trophic interactions between heterotrophic soil microbes and grazing soil invertebrates influence decomposer community composition and function. Cord-forming basidiomycete fungi are primary agents of woody litter decomposition in temperate forests. In laboratory experiments, grazing by woodlice (Isopoda) is an important factor limiting the biomass and functioning (decomposition and extracellular enzyme production) of cord-forming fungi, but its significance in the field has hitherto not been studied. Field populations of the woodlouse, Oniscus asellus, were manipulated (‘reduced’ [zero] or standardised at ‘current’ [28 m−2] or ‘double’ [56 m−2] density) in delimited plots inoculated with different fungi (un-inoculated, Hypholoma fasciculare or Phanerochaete velutina) and the effects on the microbial decomposer community assessed after 6 and 12 months. Oniscus asellus population density was reduced after 12 months in comparison to the standardised numbers at start. Significant differences between population densities remained, but varied between fungal inoculation treatments. Fatty acid analysis revealed O. asellus as a true generalist; markers for plants, fungi and bacteria were consistently abundant in storage lipids. Seasonal effects on microbial biomass and function were strong. Although woodlouse population density neither affected fungal biomass nor microbial community composition (ergosterol and soil phospholipid fatty acids), it influenced enzyme activities, depending on the inoculated fungus. Woodlice significantly reduced leucine aminopeptidase and lignin-degrading peroxidase activities, only in un-inoculated plots. In contrast, the highest woodlouse population density increased beech (Fagus sylvatica) wood decomposition and leucine aminopeptidase activity in P. velutina-inoculated plots. Increased enzyme activity and decomposition is likely a stress response, reflecting increased production of specific enzymes to provide the energy for mycelial repair and growth responses to grazing. Effects of grazing on fungal biomass and activity will be strongest at microsites of woodlouse aggregation and where forest floor woodlouse population densities are high.

Nitrogen translocation and accumulation by a cord-forming fungus (Hypholoma fasciculare) into simulated woody debris

Nitrogen (N) accumulation into woody debris is well documented, but the forms of N translocated, the mechanism through which this occurs (purportedly via translocation by cord-forming fungi) and the temporal pattern of N accumulation are not well studied. In soil microcosms, we incubated wood blocks (Pseudotsuga menziesii) inoculated with the cord-forming decay fungus Hypholoma fasciculare, and applied four forms of isotopically-labeled N (15NH4+, 15NO3-, 15N-glycine and 15N labeled litter) at the mycelial growing fronts to evaluate translocation and accumulation of diverse N sources by wood-decay fungi. Identically treated un-inoculated wood blocks were incubated. Three sampling times (6, 18 and 30days after N addition) were used to identify trends in 15N transfer and total N accumulation. Wood blocks inoculated with H. fasciculare assimilated significantly more 15N than un-inoculated blocks for all 15N treatments on at least one sampling occasion. After a total of 73days of incubation in microcosms, inoculated wood blocks increased in absolute N content by 211% relative to control blocks, but 80% of this accumulated N was lost by day 97. The small amount of 15N that was transferred into wood contrasted with the large increase in total N, suggesting that the site of N transfer was largely from soil under the wood blocks rather than at the site of 15N injection. The precipitous decline in N content was attributed to visible indications of mycelial senescence, possibly due to carbon limitation. If these findings are extrapolated to a cut-block, it follows that woody debris on the forest floor colonized by wood decay fungi would accumulate N, at least in the early stages of decay, and this process may immobilize N after harvest. If retention of N on site after harvest is a management objective, site preparation that maximizes accumulation of N in woody debris by saprotrophic fungi should be employed. This would involve homogenously distributing woody debris on site in close contact with the forest floor in order to promote fungal colonization and N accumulation.

Outcomes of fungal interactions are determined by soil invertebrate grazers

Saprotrophic fungal community composition, determined by the outcome of competitive mycelial interactions, is one of the many key factors affecting soil nutrient mineralisation and decomposition rates. Fungal communities are not generally predicted to be regulated by top-down factors, such as predation, but rather by bottom-up factors, including resource availability. We show that invertebrate grazers can exert selective pressures on fungal decomposer communities in soil, reversing the outcomes of competitive interactions. By feeding selectively on the cord-forming fungus Resinicium bicolor, isopods prevented the competitive exclusion of Hypholoma fasciculare and Phanerochaete velutina in soil and wood. Nematode populations also reversed the outcomes of competitive interactions by stimulating growth of less competitive fungi. These represent two opposing mechanisms by which soil fauna may influence fungal community composition and diversity. Factors affecting soil invertebrate communities will have direct consequences for fungal-mediated nutrient cycling in woodland soils.

Grazing by collembola affects the outcome of interspecific mycelial interactions of cord-forming basidiomycetes

While there is a plethora of studies on the effects of invertebrate grazing on mycelia, including several studies on saprotrophic cord-forming basidiomycetes, there is little information on the effects of grazing on mycelial interactions. The study compares the progress and outcomes of interspecific mycelial interactions between Hypholoma fasciculare, Phallus impudicus, Phanaerochaete velutina and Resinicium bicolor when grazed by the collembola Folsomia candida or Protaphorura armata in agar culture and trays (24 × 24 cm) of non-sterile soil. In ungrazed systems results were broadly consistent with previous studies, though there were few instances of deadlock, and a clear transitive (A > B > C) hierarchy could not be discerned. Instead, there was an intransitive hierarchy (i.e., A > B, B > C but C > A). Additionally, in agar culture, there were considerable differences in combative ability of four different strains of H. fasciculare. Collembola grazing had major effects on mycelial interactions. F. candida grazing altered both the outcome and progression of half of the fungal interactions studied, while the less active P. armata had almost no discernable effects on fungal interactions. Grazing by F. candida affected mycelial extension rate in five of the interaction combinations, some increasing, others decreasing. In grazed systems of P. velutina interacting with H. fasciculare, extension rate of the former was much more rapid over the opponent than over soil. Not only did grazing affect mycelial interactions, but interactions affected grazer activity; H. fasciculare was grazed in areas where it was interacting with P. velutina mycelium, but less so elsewhere. By altering the outcome of mycelial interactions and mycelial extension rate, collembola grazing may alter the distribution of cord-forming fungi on the forest floor, and may also play a role in maintaining the diversity of fungal species. The differences in combative ability of different strains of a species imply an even more complex scenario in the natural world.

Growth-induced mass flows in fungal networks.

Cord-forming fungi form extensive networks that continuously adapt to maintain an efficient transport system. As osmotically driven water uptake is often distal from the tips, and aqueous fluids are incompressible, we propose that growth induces mass flows across the mycelium, whether or not there are intrahyphal concentration gradients. We imaged the temporal evolution of networks formed by Phanerochaete velutina, and at each stage calculated the unique set of currents that account for the observed changes in cord volume, while minimizing the work required to overcome viscous drag. Predicted speeds were in reasonable agreement with experimental data, and the pressure gradients needed to produce these flows are small. Furthermore, cords that were predicted to carry fast-moving or large currents were significantly more likely to increase in size than cords with slow-moving or small currents. The incompressibility of the fluids within fungi means there is a rapid global response to local fluid movements. Hence velocity of fluid flow is a local signal that conveys quasi-global information about the role of a cord within the mycelium. We suggest that fluid incompressibility and the coupling of growth and mass flow are critical physical features that enable the development of efficient, adaptive biological transport networks.

Grazing by Folsomia candida (Collembola) differentially affects mycelial morphology of the cord-forming basidiomycetes Hypholoma fasciculare, Phanerochaete velutina and Resinicium bicolor

Cord-forming basidiomycetes are important decomposers of dead wood in forest ecosystems but the impact of mycophagous soil invertebrates on their mycelia are little known. Here we investigate the effects of different grazing intensities of Collembola ( Folsomia candida) on mycelial foraging patterns of the saprotrophic cord-forming basidiomycetes Hypholoma fasciculare, Phanerochaete velutina and Resinicium bicolor growing from beech ( Fagus sylvatica) wood block inocula in dishes of non-sterile soil. Mycelial extension rate and hyphal coverage decreased with increased grazing intensity. R. bicolor was most affected, high grazing density resulting in only a few major cords remaining. Grazing of H. fasciculare often resulted in points of more rapid outgrowth as cords with a fanned margin. In grazed mycelia of P. velutina the main cords had fanned tips and lateral cords became branched. These results suggest that mycophagy by Collembola may hinder the growth of cord-forming fungi in woodlands, which might impact on the ability of these fungi to forage for and decompose dead organic material.

Saprotrophic mycelial cord abundance, length and survivorship are reduced in the conversion of tropical cloud forest to shaded coffee plantation

One of the most conspicuous soil elements of the tropical cloud forest in central Veracruz, mycelial cord-forming fungi, is strongly affected by the conversion of forest into shaded coffee plantations. Mycelial cord-forming fungi are less abundant, smaller and have a sharper mortality rate in shaded coffee plantations than in relatively conserved forest sites. I present evidence that suggests that changes in soil microenvironmental conditions affect the abundance of mycelial cord forming fungi. These results lend further support to growing evidence that the biodiversity of the understorey and soil are not being conserved within shaded coffee plantations. This contrasts markedly with other studies that suggest that over storey biota is effectively conserved by this conversion.

Collembolan grazing affects the growth strategy of the cord-forming fungus Hypholoma fasciculare

Mycelia of cord-forming fungi show remarkable patterns of reallocation of biomass and nutrients indicating an important role of these, often extensive, organisms in the spatial translocation of energy and nutrients in forest soils. Despite the rich tradition of interaction studies between soil microarthropods and fungi, the spatial implications of these interactions, due to the potential growth responses of the fungi and to the translocation of energy and nutrients within the mycelial network, have been largely ignored. In this paper we analyse fungal growth responses in two-dimensional model systems composed of compressed soil, the cord-forming fungus Hypholoma fasciculare and three fungivorous Collembolan species. We hypothesised that (i) the highly co-ordinated nature of cord-forming fungi would lead to growth responses following collembolan grazing, and that, (ii) such changes are dependent on grazing intensity, and (iii) changes are dependent on the species grazing. Mycelial extent and hyphal cover decreased with increasing grazing density; at highest grazing density also the fractal dimension of the mycelial border decreased, indicating a less branched foraging front due to the regression of fine hyphae and the development of mycelial cords. Effects differed greatly between collembolan species although they exerted comparable grazing pressure (the smaller species were added in larger numbers according to their allometric size-metabolic rate relationships): while grazing by Folsomia candida resulted in less mycelial extension and hyphal cover, these variables were not affected when Proisotoma minuta and Hypogastrura cf. tullbergi grazed. The effects of a species mix suggested an additive effect of the component species. This shows that fungal mycelia may suffer from damage caused by few but large collembolans, affecting extension as well as coverage of the mycelium, but that fungi may compensate for the biomass loss caused by more but slightly smaller collembolans. In about 20% of the model systems H. fasciculare switched from a growth pattern with a broad contiguous foraging front and uniform growth in all directions to a pattern with fast growing sectors while other sectors stopped growth completely. The switch occurred in grazed systems exclusively; thus we interpret this observation as a fugitive response and as a strategy for quickly escaping from places where grazing pressure is experienced.

Saprotrophic Cord-Forming Fungi: Meeting the Challenge of Heterogeneous Environments

Saprotrophic Cord-Forming Fungi: Meeting the Challenge of Heterogeneous Environments

Saprotrophic cord-forming fungi: meeting the challenge of heterogeneous environments

Many saprotrophic fungi, especially basidiomycetes, which are able to grow out of the substratum that they are colonizing in search of new resources (i.e., nonresource-unit-restricted fungi) form mycelial cords, which are aggregations of predominantly parallel, longitudinally aligned hyphae. These cords often form extensive, long-lived systems which interconnect discrete nutrient resources, e.g. woody litter components, on the floor of boreal, temperate and tropical forests, and some can form networks in tropical canopies. They exhibit foraging strategies which vary among species, and which alter depending on resource quantity and quality, the presence of other organisms, and microclimatic environment. The morphological patterns they form are well described by fractal geometry. Their mycelia show remarkable patterns of reallocation of biomass and mineral nutrients when new resources are encountered during mycelial foraging or when new resources are added to mature systems. Mycelial-cord systems encountering heterogeneously distributed organic substrata coordinate use of available resources so that demands are met by ‘spreading the load’ through the system. The persistent networks, ability to forage for new resources, and ability to reallocate mycelial biomass and nutrients exhibited by saprotrophic cord-forming fungi provide a solution to the problems of life in a spatially and temporally heterogenous environment. Response to the heterogenous environment in which these fungi exist generates heterogeneity in themselves, and they in turn generate heterogeneity in their environment, both in space and time.

Development of Phanerochaete velutina mycelial cord systems: effect of encounter of multiple colonised wood resources

Abstract The effect of decay and presence of fungi, in combinations of wood resources, on the foraging behaviour of the saprotrophic cord-forming fungus Phanerochaete velutina was examined. P. velutina was affected by both resource decay state and the presence of other wood decay species within the resource, and preferentially colonised resources offering an easy prospect of successful colonisation and high nutrient availability. Partially decayed resources which had been autoclaved were preferentially colonised, probably due to the availability of nutrients released by the death of the precolonising fungus and lack of competition/combat. The presence of a viable and long-established precolonising species within the resource made it `unattractive'. Some precolonising fungi (e.g. Xylaria polymorpha) were better able to resist an attack by P. velutina than others (e.g. Bjerkandera adusta).

Development of Phanerochaete velutina mycelial cord systems: effect of encounter of multiple colonised wood resources

The effect of decay and presence of fungi, in combinations of wood resources, on the foraging behaviour of the saprotrophic cord-forming fungus Phanerochaete velutina was examined. P. velutina was affected by both resource decay state and the presence of other wood decay species within the resource, and preferentially colonised resources offering an easy prospect of successful colonisation and high nutrient availability. Partially decayed resources which had been autoclaved were preferentially colonised, probably due to the availability of nutrients released by the death of the precolonising fungus and lack of competition/combat. The presence of a viable and long-established precolonising species within the resource made it `unattractive'. Some precolonising fungi (e.g. Xylaria polymorpha) were better able to resist an attack by P. velutina than others (e.g. Bjerkandera adusta).

Development of mycelial systems of Stropharia caerulea and Phanerochaete velutina on soil: effect of temperature and water potential

Effect of temperature and water potential on extension rate, extra-resource biomass and fractal dimension of Stropharia caerulea and Phanerochaete velutina growing in trays of soil was determined non-destructively with time, by image analysis. S. caerulea responded differently from P. velutina , mycelial extension and biomass production rates of the former being considerably affected by changes in temperature and water potential, with greater aggregation of mycelia into cords at 25°C and at and below -0.02 MPa. These morphological changes were reflected in the fractal dimension values. Mycelial extension of S. caerulea on agar was sensitive to temperatures above 25° and water potentials below -1.3 MPa. This is the first reported work on abiotic effects on fractal dimension of cord-forming fungi on soil, and these results are discussed in terms of the function of mycelial cords and foraging strategies.

Fungal colonization of hardwood stumps from natural sources: II. Basidiomycetes

Chemical treatment and tree species markedly influenced both the assemblage of basidiomycete species colonizing cut stumps of beech, birch and oak, and their pattern of colonization. Colonization by Phlebia merismoides was strongly promoted by treatment with 40% ammonium sulphamate (AMS), whilst, in oak, Hypholoma fasciculare and Phanerochaete velutina preferentially colonized water-treated controls, and in birch, Chondrostereum purpureum, was more frequent in stumps treated with 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and controls, than in those treated with AMS. AMS treatment led to more extensive decay in stumps, especially in the outermost wood where fungi capable of subcortical mycelial growth, e.g. P. merismoides, H. fasciculare and P. velutina, often developed. In oak, decay caused by basidiomycetes extended rapidly down to the root-collar of AMS-treated stumps, but the roots remained uncolonized. In those treated with 2,4,5-T and in controls, colonization was restricted to the vicinity of the cut surface. In contrast, in birch and beech stumps treated with AMS, decay extended rapidly into the roots. In beech, after 2 1/2 years, cord-forming fungi such as Phallus impudicus and Phanerochaete velutina were frequently present. In birch, decay also developed in roots of controls.