Hyphal Coverage Research Articles

Fungal degradation of bamboo treated with crude lake salt and a mixture of borax and boric acid

This study compared the effectiveness of crude lake salt, a traditional preservative used by artisans in Uganda, and borax-boric acid, a conventional preservative, against fungal degradation. Using the European standard, an experiment was set up to determine the durability of Oxytenanthera abyssinica, Oldeania alpina and Bambusa vulgaris treated with 2 % and 6 % crude lake salt and borax-boric acid against Gloeophyllum trabeum, Coniophora puteana and Trametes versicolor. Mass loss comparisons between treated and untreated bamboo samples were made. Durability classes were assigned according to the amount of mass lost. Bamboo samples exposed to G. trabeum had lower surface hyphal coverage compared to those exposed to C. puteana and T. versicolor irrespective of the preservative used. Samples treated with borax-boric acid were in durability class I compared to those treated with crude lake salt that were between class II and III according to European standard. The lowest mass loss for bamboo treated with crude lake salt was 5.9 % in O. abyssinica exposed to G. trabeum. The highest mass loss for bamboo treated with crude lake salt was 14.24 % in B. vulgaris exposed to T. Versicolor. The study confirmed that while artisans use crude lake salt as a traditional preservative, it does not protect against white and brown rot while all concentrations of borax-boric acid provided protection against all fungi.

Foraging strategies of fungal mycelial networks: responses to quantity and distance of new resources.

Fungal mycelial networks are essential for translocating and storing water, nutrients, and carbon in forest ecosystems. In particular, wood decay fungi form mycelial networks that connect various woody debris on the forest floor. Understanding their foraging strategies is crucial for complehending the role of mycelium in carbon and nutrient cycling in forests. Previous studies have shown that mycelial networks initiate migration from the original woody resource (inoculum) to a new woody resource (bait) if the latter is sufficiently large but not if it is small. However, the impact of energetic costs during foraging, such as the distance to the bait, has not been considered. In the present study, we conducted full-factorial experiments with two factors, bait size (4 and 8cm3) and distance from the inoculum (1 and 15cm). An inoculum wood block, colonized by the wood decay fungus Phanerochaete velutina, was placed in one corner of a bioassay dish (24cm × 24cm) filled with unsterilized soil. Once the mycelium grew onto the soil to a distance >15cm from the inoculum, a sterilized new bait wood block (of either size) was placed on the soil at one of the two distances to be colonized by the mycelia from the inoculum. After 50days of incubation, the baits were harvested, and their dried weight was measured to calculate the absolute weight loss during incubation. The inoculum wood blocks were retrieved and placed on a new soil dish to determine whether the mycelium would grow out onto the soil again. If no growth occurred within 8days of additional incubation, we concluded that the mycelium had migrated from the inoculum to the bait. The results showed that mycelia in inocula coupled with baits positioned 1cm away migrated to the baits more frequently than those with baits positioned 15cm away. A structural equation model revealed that bait weight loss (energy gain) and hyphal coverage on the soil (foraging cost) significantly influenced mycelial migration decisions. These findings suggest that fungal mycelia may employ their own foraging strategies based on energetic benefits.

Wood species identity alters dominant factors driving fine wood decomposition along a tree diversity gradient in subtropical plantation forests

AbstractMicroclimate and biotic factors drive wood decomposition. Yet, relatively few studies have been conducted in warmer tropical and subtropical forests compared with colder temperate and boreal forests, where climate might have stronger limitations on decomposition. Besides, conclusions on decomposition are generally based on single wood species or standardized materials. Thus, a general assessment if wood species identity alters dominant factors of decomposition in subtropical forest could improve the predictability of current C cycle models. We measured fine wood mass‐loss rates of seven widespread tree species in southeast China at two time steps (after 1 and 2 years) in subtropical plantation forests with tree species diversity manipulated. We found that termites exceeded fungi in consuming fine woody debris, and termite foraging intensity decreased with lignin content. Tree species diversity increased fungal hyphal coverage on fine wood samples and had different effects on wood mass‐loss rates depending on wood species. Higher minimum temperature and amplitude of relative humidity suppressed termite foraging intensity, with humidity having inconsistent effects on mass‐loss rates among wood species. Interestingly, microclimate outweighed biotic factors for Castanopsis eyrei but not for the other species. Three traits, that is, wood density, phenolics, and lignin content, were higher than the average for C. eyrei, making it the least attractive species for decomposers. Our findings suggest that species identity influences the effects and relative importance of biotic factors and microclimate for wood decomposition in subtropical forests. Furthermore, species identity effects are possibly mediated by multiple wood traits.Abstract in Chinese is available with online material.

Effects of wood resource size and decomposition on hyphal outgrowth of a cord-forming basidiomycete, Phanerochaete velutina

To assess the relationship between resource use and hyphal growth in a cord-forming basidiomycete, Phanerochaete velutina, soil microcosm experiments were conducted using wood blocks of three different sizes in three different soil quantities, thereby simulating the different amounts of available nutrients. The highest percentage weight loss was observed in the smallest wood blocks after a 27-d incubation period in soil microcosms, although the percentage weight loss over the 2-month pure culture colonization prior to inoculation was not significantly different among various block sizes. The greatest hyphal outgrowth was also observed in the smallest wood blocks and was positively associated with wood decay. The slopes of the regression lines between hyphal coverage and percentage wood mass loss were identical among different wood sizes, but the slopes between hyphal coverage and absolute wood mass loss were steeper in the smaller wood blocks than that in largest one. These results suggest that the level of intensity of mycelial foraging for new resources in the soil depends on the percentage of the amount of wood resource utilized, and not on the absolute amount of carbon obtained from the wood.

Production and effects of volatile organic compounds during interspecific interactions

Competition between mycelia of saprotrophic cord-forming basidiomycetes occurs both within dead woody resources and in the soil-litter interface, and involves a variety of antagonistic mechanisms including the production of volatile organic compounds (VOCs). The antagonistic potential of VOC profiles from interactions in wood blocks and in soil microcosms was assessed using shared headspace experiments, and the profile of VOCs emitted over the course of interactions elucidated using solid phase microextraction (SPME) with gas chromatography-mass spectrometry (GC–MS). Quantitative and qualitative changes in VOC production occurred in interactions compared to self-pairing controls, with different VOC profiles from fungi growing in wood blocks compared to soil trays. There were both stimulatory and inhibitory effects of VOCs on target mycelial extension rate, hyphal coverage and fractal dimension. VOC-mediated effects were greater in self-pairing controls compared to interactions, and differed depending on the substratum in which the VOC-producing fungi were growing.

Fungal growth necessary but not sufficient for effective biopulping of wood for lignocellulosic ethanol applications

A lignocellulosic biomass treatment method utilizing wood rot fungi to improve cellulosic sugar solubilization for ethanol production was modified to provide larger samples for chemical analyses. Liriodendron tulipifera wood chips were treated in a novel application of aerobic polypropylene “spawn bags” as experimental bioreactors for biopulping. Treatments were inoculated with culture suspensions of white rot ( Ceriporiopsis subvermispora) and brown rot ( Postia placenta) fungi in 40 day incubations. Fungal growth occurred in all treatments, with extensive hyphal coverage of the biomass (ca. >80% of wood chip surfaces). After treatment, physical biodegradation, holocellulose, α-cellulose, and lignin contents of the fungal-biopulped wood chips were comparable to previous results. However, unlike in previous studies, the biopulped wood did not exhibit significant increases in soluble sugars after enzymatic hydrolysis. These results demonstrate that extensive fungal colonization of biomass is not necessarily sufficient for effective biopulping to increase production of free soluble sugars from wood. Environmental controls on hydrolytic activity by wood rot fungi are poorly known, but we hypothesize that treatment inoculation using nitrogen rich medium may have inhibited lignin-specific fungal hydrolysis of the wood. Future development of effective, standardized biopulping techniques for improving soluble sugar production from lignocellulosic biomass will require optimization of methods including characterization of inoculation nutrients and container effects on fungal metabolic activity.

Species-specific effects of grazing invertebrates on mycelial emergence and growth from woody resources into soil

Extensive studies on the grazing of young basidiomycete mycelial systems by invertebrates have revealed effects on extension rate, hyphal coverage and fractal geometry. To date, no studies have compared the grazing effects of different invertebrates on the ability of fungi to emerge from wood and establish mycelial systems in soil. Here, the effects of six soil invertebrate taxa on mycelial emergence and subsequent development of six basidiomycetes were compared. Woodlouse (Oniscus asellus), millipede (Blaniulus guttulatus), oribatid mite (Euzetes globulus), collembola (Folsomia candida), enchytraeid (Enchytraeus crypticus) and nematode (Panagrellus redivivus) populations were allowed to graze Phanerochaete velutina, Resinicium bicolor, Phallus impudicus and three different isolates of Hypholoma fasciculare mycelia as they emerged from beech (Fagus sylvatica) wood-inocula in 2-dimensional soil-tray microcosms. Impacts varied between invertebrate taxa, ranging from woodlice which affected mycelial development of all fungal isolates and completely prevented mycelial growth in two fungal species, to mites and enchytraeids which had no discernable effect on any of the fungi. Grazing impacts also varied between and within fungal species. Wood decay rates were affected with implications for nutrient mineralisation and decomposition.

Non‐trophic effects of oribatid mites on cord‐forming basidiomycetes in soil microcosms

1. Saprotrophic cord‐forming basidiomycetes are the primary agents of decomposition in forest ecosystems. Collembola and oribatid mites affect fungal growth and foraging, and therefore decomposition, through direct mycelial grazing.2. Grazing on the fungal species Hypholoma fasciculare, Resinicium bicolor and Phanerochaete velutina by the collembola Folsomia candida, and the oribatid mites Steganacarus magnus, Euzetes globulus and Hermannia gibba was investigated in soil microcosms.3. Folsomia candida grazed on all fungal species: radial extent of R. bicolor, hyphal coverage of all fungal species, and fractal dimension of R. bicolor and P. velutina were all reduced. Oribatid mites did not graze the fungi but did affect mycelial morphology. Steganacarus magnus caused a reduction in the radial extent of H. fasciculare, and the hyphal coverage and fractal dimension in both H. fasciculare and R. bicolor. Euzetes globulus and H. gibba reduced the hyphal coverage of P. velutina.4. Oribatid mites are associated with a cornucopia of chemical secretions with possible anti‐fungal properties. Chemical analysis of H. gibba opisthonotal secretions revealed four main compounds, all of which are new to the known spectrum of opisthonotal components. The most abundant was (E)‐β‐farnesene.5. Treatment effects were species‐specific in terms of both fungal and invertebrate species. This study provides the first evidence of non‐grazing effects of oribatid mites on fungal growth and morphology. This could potentially influence the spatial organisation of mycelium in forest soils and therefore the ability of fungi to locate, colonise and decompose dead organic matter.

Species-specific impacts of collembola grazing on fungal foraging ecology

Fungi are primary agents of organic matter decomposition in forests. Although invertebrate grazing affects fungal biomass and morphology, the species-specific consequences of these interactions are little understood. Using three collembola species ( Folsomia candida, Protaphorura armata, Proisotoma minuta) we employed a multi-trophic approach to investigate the individual effects of invertebrate grazing on four species of saprotrophic basidiomycete fungi growing in two species (one fungus: one collembola) soil microcosms. We studied these effects at three trophic levels: the rate of wood decay brought about by the fungi was assessed; fungal growth was characterized across multiple time points using a range of image analysis parameters (radial extension, hyphal coverage, fractal dimension); and collembola abundance was determined at the end of the experiment. Collembola species had different impacts both within and across fungal species; F. candida had the greatest effect on fungal mycelia whereas P. armata often had little impact. Fungal species varied in their resilience to grazing; all collembola species modified Phanerochaete velutina and Hypholoma fasciculare morphology, that of Resinicium bicolor was only markedly affected by F. candida, and effects on Phallus impudicus were negligible. In the case of H. fasciculare, these grazing effects translated into effects on the rate of fungus-induced wood decay: F. candida and P. armata, but not P. minuta, reduced wood decay rate compared to ungrazed controls. Rate of wood decay was unaffected in the other three fungal species. Changes in collembola population size were generally consistent across fungal species, with each species achieving a greater abundance on P. velutina than on H. fasciculare and P. impudicus. The collembola species did, however, respond differently to R. bicolor, with F. candida being more successful than P. armata. Our study suggests that a wide range of impacts can occur during fungus–collembola interactions, and that caution should be exercised when treating saprotrophic fungi and mycophagous collembola as uniform functional components.

Hyphal-mediated transfer of nitrate, arsenic, cesium, rubidium, and strontium between arbuscular mycorrhizal forbs and grasses from a California oak woodland

Arbuscular mycorrhizal (AM) fungi colonize most plant species in the savannah/oak woodland ecosystem of the California Sierra Foothills. These fungi may form belowground linkages between plant root systems, potentially altering nutrient transfers. In a laboratory experiment with two-chambered pots where only AM fungal hyphae connected the chambers, we examined nutrient transfer between native plant species of grasses and forbs. Two separate chambers with plants were separated by a set of two stainless steel screens (25 μm mesh) separated by a 1 cm air gap. These screens successfully restricted root growth but allowed hyphal coverage (15–100% of the area) of the screens. Nutrient transfers were monitored by applying nitrogen ( 15N), arsenic (P analog), strontium (Ca analog), and cesium and rubidium (K analogs). The analogs and 15N were applied to leaves of donor plants for 48 h. We observed transfer of 15N, As, Cs, and Rb from donor shoots to receiver shoots. Element transfers were not correlated with receiver biomass or donor concentrations. Transfers varied among the elements and plant combinations. Both Rb and Cs (K analogs) had the same pattern of transfer. Nitrogen was transferred in greatest amounts and between forbs and grasses, and grasses acted as a stronger sink for N. Forbs were generally the stronger sink for As. Fungal hyphae facilitated transfer among forbs and grasses, suggesting that they have a key role in nutrient transfer in California oak woodlands.

Compensatory growth of Phanerochaete velutina mycelial systems grazed by Folsomia candida (Collembola)

Phanerochaete velutina is a major agent of wood decomposition in temperate forests. It grows out of woody resources in search of other resources and is then vulnerable to grazing by invertebrates. The aim of this study was to determine how continuous grazing and grazing for only 2 days by different densities of collembola, Folsomia candida, affect mycelial development (radial extension, hyphal coverage and fractal dimension) of P. velutina growing across non-sterile soil. High density (80 collembola) continuous grazing resulted in different mycelial foraging patterns compared to controls and lower density (20 and 40 collembola) continuous grazing: radial extension rate was reduced from 8.4 mm day(-1) (control) to 6.9 mm day(-1) (80 collembola), hyphal coverage was reduced to 81% of controls and mass fractal dimension increased from 1.68 (control) to 1.72 (80 collembola). There was evidence of over-compensatory growth: when high density grazing ceased the new growth was considerably greater (38%) than in controls. Grazing also resulted in growth stimulation: at low density continuous grazing (20 collembola) hyphal coverage was 15.6% greater than in controls. The ecological implications of compensatory and stimulatory growth in fungal-invertebrate interactions are considered.

Reorganization of mycelial networks of Phanerochaete velutina in response to new woody resources and collembola ( Folsomia candida) grazing

Mycelial development of Phanerochaete velutina extending from wood inocula in 57 × 57 cm trays of non-sterile soil was characterized after adding: (1) collembola; (2) new wood resources; (3) both new wood resources and collembola; and (4) no new resources and no collembola. After 99 d, all systems had produced distinct mycelial cords, much of the diffuse mycelium and thinner cords that were produced early on having regressed. Systems to which new resources (but no collembola) had been added developed thick cords interconnecting inocula with new resources, and much of the non-connected mycelium regressed. Nonetheless, these systems had significantly greater hyphal coverage and mass fractal dimension than the other treatments, resulting from outgrowth from the new resources. Unexpectedly, morphology of grazed systems with no added resources was very similar to that of ungrazed systems with no added resources, apparently because the collembola grazed on senescing hyphae that would ultimately have regressed. Where new resources and collembola were added, there was proliferation of fine mycelium along connective cords and elsewhere, but this was not as extensive as in the new resource/no collembola systems, the fine mycelium apparently being grazed in patches. Fungus gnat (family Sciaridae) larvae contaminated eight (out of 14) trays with no added collembola, but none of the systems to which collembola had been added. They burrowed around the wood and caused cords to be severed.

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.

Nutrient Movement and Mycelial Reorganization in Established Systems of Phanerochaete velutina, Following Arrival of Colonized Wood Resources

The effect of arrival of wood resources, pre-colonized by Coriolus versicolor, Phlebia radiata, Stereum hirsutum, and Vuilleminia comedens, on mycelial systems of Phanerochaete velutina was studied in trays of nonsterile soil in the laboratory over 5 months. Morphological responses were quantified non-destructively using image analysis. In a parallel series of experiments, nutrient movement was also quantified non-destructively using (32)P monitoring with a scintillation probe and subsequently by destructively harvesting after 155 days. The presence of a fungus occupying a newly arriving resource had major effects on deployment of biomass and on the uptake and allocation of phosphorus in the established Pha. velutina system. The effects varied depending on the species occupying the new resource. Hyphal coverage was greater in the half of the system to which new resources were added. Following addition of new resources, there was massive redeployment of biomass away from regions with no new resource when the new resource was (1) uncolonized, (2) colonized by V. comedens, or (3) colonized by S. hirsutum (although to a lesser extent with the latter), but not with others. (32)P was taken up by Pha. velutina both in the vicinity of the inoculum and the new resource and was translocated to the new resource from both sites of uptake; however, the local supply contributed most. Bidirectional translocation also occurred. The results are discussed in relation to mycelial foraging strategies, nutrient translocation, and partitioning within mycelial cord systems.

Mycelial responses of Hypholoma fasciculare to collembola grazing: effect of inoculum age, nutrient status and resource quality

The effects of grazing by the collembolan Folsomia candida on mycelial foraging patterns of Hypholoma fasciculare growing from beech (Fagus sylvatica) wood block inocula in trays of non-sterile soil was investigated. The wood inocula differed in size, state of decay (time for which wood has been colonized: 2 yr, 1 yr, 6 and 3 months) and nutrient status (inocula colonized on malt agar or nutrient agar). Mycelia were most luxuriant, had greater hyphal coverage and extended more rapidly from 2 yr old than younger inocula, from 4 cm3 than 1 cm3 inocula, and from inocula colonized on malt extract agar rather than on distilled water agar. Grazing dramatically reduced coverage and extension, especially in the less luxuriant systems characterized by many fine hyphae and fewer mycelial cords. Grazing by collembola often resulted in points of more rapid outgrowth as cords with a fanned margin. Results are discussed in terms of fungal foraging strategies.

Mycelial foraging by Resinicium bicolor: interactive effects of resource quantity, quality and soil composition

The mycelial response of the wood-rotting basidiomycete Resinicium bicolor to the nutritional status of its environment, the interactive effects of food base quantity and quality and of soil composition were investigated in trays of forest soil. Effects on mycelial extension, hyphal coverage and mycelial morphology (described by fractal dimensions, D) were quantified. Mycelial extension rate, rate of increase in hyphal coverage and D all increased with increasing inoculum size. Inoculum quality affected development: extension and rate of increase of hyphal coverage were faster when inocula had been originally colonised by cultures growing on malt agar than on water agar, and by inocula colonised for 3 months rather than 12 months. Soil carbon status and/or structure also affected development, with the slowest extension and hyphal coverage occurring on ashed and unamended soils with the lowest carbon status. Morphology was dramatically altered on ashed soils (zero carbon), where extremely crooked cords developed in contrast to relatively straight, occasionally branching cords which formed in non-ashed soils. Results are discussed in relation to fungal foraging.

Mycelial foraging by Resinicium bicolor: interactive effects of resource quantity, quality and soil composition

The mycelial response of the wood-rotting basidiomycete Resinicium bicolor to the nutritional status of its environment, the interactive effects of food base quantity and quality and of soil composition were investigated in trays of forest soil. Effects on mycelial extension, hyphal coverage and mycelial morphology (described by fractal dimensions, D) were quantified. Mycelial extension rate, rate of increase in hyphal coverage and D all increased with increasing inoculum size. Inoculum quality affected development: extension and rate of increase of hyphal coverage were faster when inocula had been originally colonised by cultures growing on malt agar than on water agar, and by inocula colonised for 3 months rather than 12 months. Soil carbon status and/or structure also affected development, with the slowest extension and hyphal coverage occurring on ashed and unamended soils with the lowest carbon status. Morphology was dramatically altered on ashed soils (zero carbon), where extremely crooked cords developed in contrast to relatively straight, occasionally branching cords which formed in non-ashed soils. Results are discussed in relation to fungal foraging.