Fungal Decomposers Research Articles

Phenotypic plasticity of fungal traits in response to moisture and temperature

Phenotypic plasticity of traits is commonly measured in plants to improve understanding of organismal and ecosystem responses to climate change but is far less studied for microbes. Specifically, decomposer fungi are thought to display high levels of phenotypic plasticity and their functions have important implications for ecosystem dynamics. Assessing the phenotypic plasticity of fungal traits may therefore be important for predicting fungal community response to climate change. Here, we assess the phenotypic plasticity of 15 fungal isolates (12 species) from a Southern California grassland. Fungi were incubated on litter at five moisture levels (ranging from 4–50% water holding capacity) and at five temperatures (ranging from 4–36 °C). After incubation, fungal biomass and activities of four extracellular enzymes (cellobiohydrolase (CBH), β-glucosidase (BG), β-xylosidase (BX), and N-acetyl-β-D-glucosaminidase (NAG)) were measured. We used response surface methodology to determine how fungal phenotypic plasticity differs across the moisture-temperature gradient. We hypothesized that fungal biomass and extracellular enzyme activities would vary with moisture and temperature and that the shape of the response surface would vary between fungal isolates. We further hypothesized that more closely related fungi would show more similar response surfaces across the moisture-temperature gradient. In support of our hypotheses, we found that plasticity differed between fungi along the temperature gradient for fungal biomass and for all the extracellular enzyme activities. Plasticity also differed between fungi along the moisture gradient for BG activity. These differences appear to be caused by variation mainly at the moisture and temperature extremes. We also found that more closely related fungi had more similar extracellular enzymes activities at the highest temperature. Altogether, this evidence suggests that with global warming, fungal biodiversity may become increasingly important as functional traits tend to diverge along phylogenetic lines at higher temperatures.

Lower relative abundance of ectomycorrhizal fungi under a warmer and drier climate is linked to enhanced soil organic matter decomposition.

The aboveground impacts of climate change receive extensive research attention, but climate change could also alter belowground processes such as the delicate balance between free-living fungal decomposers and nutrient-scavenging mycorrhizal fungi that can inhibit decomposition through a mechanism called the Gadgil effect. We investigated how climate change-induced reductions in plant survival, photosynthesis and productivity alter soil fungal community composition in a mixed arbuscular/ectomycorrhizal (AM/EM) semiarid shrubland exposed to experimental warming (W) and/or rainfall reduction (RR). We hypothesised that increased EM host plant mortality under a warmer and drier climate might decrease ectomycorrhizal fungal (EMF) abundance, thereby favouring the proliferation and activity of fungal saprotrophs. The relative abundance of EMF sequences decreased by 57.5% under W+RR, which was accompanied by reductions in the activity of hydrolytic enzymes involved in the acquisition of organic-bound nutrients by EMF and their host plants. W+RR thereby created an enhanced potential for soil organic matter (SOM) breakdown and nitrogen mineralisation by decomposers, as revealed by 127-190% increases in dissolved organic carbon and nitrogen, respectively, and decreasing SOM content in soil. Climate aridification impacts on vegetation can cascade belowground through shifts in fungal guild structure that alter ecosystem biogeochemistry and accelerate SOM decomposition by reducing the Gadgil effect.

Factors affecting the quantity and type of tree-related microhabitats in Mediterranean mountain forests of high nature value

Tree-related microhabitats (hereafter TreMs) are structures occurring on trees, such as rot holes, cavities, large nests, mould, fruiting bodies and mycelia of decomposer fungi. TreMs have been widely recognized as important substrates and structures useful for biodiversity conservation in forest ecosystems, and they can be used as indicators for describing and monitoring forest naturalness. However, most studies on the occurrence of TreMs have been mainly done in forest ecosystems of Central Europe, while less research has been conducted in Mediterranean mountain forests. In this study, we investigated the diversity and abundance of 23 types of TreMs on living trees and on deadwood in seven Mediterranean mountains unmanaged forests located in the Apennines (Italy). The abundance of TreMs was evaluated by counting the number of TreMs per tree, while the diversity of TreMs was evaluated by means of the Shannon-Wiener index. We focused on the relationships between diversity and abundance of TreMs, and tree size (e.g., diameter, height, volume), and the time since the last harvest. Among the investigated stands, 2612 living trees, 457 standing dead trees and snags, and 1247 lying deadwood pieces were analysed. For living trees, a generalized linear mixed model was applied to test the effect of several variables on the abundance of TreMs per tree. Diameter at breast height (DBH) of tree stems influenced the abundance and diversity of TreMs. The time since the last harvest also significantly affected the probability that TreMs could be formed in a long-term perspective. The interaction of the predictors “DBH2” and “Years since the last harvest” generated a better model than the one in which the two variables were kept separate. Indeed, these two factors together would better represent the transition of a previously managed forest to a more natural state over time. This study might provide useful information to land managers committed to forestry practices towards sustainable management and biodiversity conservation, especially referring to survey and inventory of forests of high nature value.

Nutrient limitation may induce microbial mining for resources from persistent soil organic matter.

Fungi and bacteria are the two principal microbial groups in soil, responsible for the breakdown of organic matter (OM). The relative contribution of fungi and bacteria to decomposition is thought to impact biogeochemical cycling at the ecosystem scale, whereby bacterially dominated decomposition supports the fast turnover of easily available substrates, whereas fungal-dominated decomposition leads to the slower turnover of more complex OM. However, empirical support for this is lacking. We used soils from a detritus input and removal treatment experiment in an old-growth coniferous forest, where above- and belowground litter inputs have been manipulated for 20yr. These manipulations have generated variation in OM quality, as defined by energetic content and proxied as respiration per g soil organic matter (SOM) and the δ13 C signature in respired CO2 and microbial PLFAs. Respiration per g SOM reflects the availability and lability of C substrate to microorganisms, and the δ13 C signature indicates whether the C used by microorganisms is plant derived and higher quality (more δ13 C depleted) or more microbially processed and lower quality (more δ13 C enriched). Surprisingly, higher quality C did not disproportionately benefit bacterial decomposers. Both fungal and bacterial growth increased with C quality, with no systematic change in the fungal-to-bacterial growth ratio, reflecting the relative contribution of fungi and bacteria to decomposition. There was also no difference in the quality of C targeted by bacterial and fungal decomposers either for catabolism or anabolism. Interestingly, respired CO2 was more δ13 C enriched than soil C, suggesting preferential use of more microbially processed C, despite its lower quality. Gross N mineralization and consumption were also unaffected by differences in the ratio of fungal-to-bacterial growth. However, the ratio of C to gross N mineralization was lower than the average C/N of SOM, meaning that microorganisms specifically targeted N-rich components of OM, indicative of selective microbial N-mining. Consistent with the δ13 C data, this reinforces evidence for the use of more microbially processed OM with a lower C/N ratio, rather than plant-derived OM. These results challenge the widely held assumption that microorganisms favor high-quality C sources and suggest that there is a trade-off in OM use that may be related to the growth-limiting factor for microorganisms in the ecosystem.

Root influence on soil nitrogen availability and microbial community dynamics results in contrasting rhizosphere priming effects in pine and spruce soil

Abstract The rhizosphere priming effect (RPE) is increasingly considered an important regulator of below‐ground C and N cycling, with implications for terrestrial ecosystem feedback to global change. Even so, there is a lack of knowledge about the mechanisms underlying RPEs. We used novel stable isotope probing methods to investigate RPEs in an experiment with Scots pine and Norway spruce seedlings, two of the most common boreal forest species. We determined root exudation rates, RPEs on SOM decomposition and gross N mineralization, and the contribution of different microbial functional groups to the observed RPEs. Pine induced positive and spruce induced negative RPEs on SOM decomposition, while no RPE on gross N mineralization was observed. Negative RPEs in the spruce treatment were attributed to an opportunistic subset of the fungal community that was growing on root‐derived 13C while depleting available N, thus reducing the activity of microbial SOM decomposers. In the pine treatment, available N was likely sufficient to support the root‐induced decomposition activities of fungal decomposers, resulting in positive RPEs. The findings suggest that RPEs, promoted by root stimulation of distinct subsets of the microbial community, can either contribute to conserving the soil C stock or to depleting it, depending on plant species and soil N availability. A free Plain Language Summary can be found within the Supporting Information of this article.

Exploring Trait Trade-Offs for Fungal Decomposers in a Southern California Grassland.

Fungi are important decomposers in terrestrial ecosystems, so their responses to climate change might influence carbon (C) and nitrogen (N) dynamics. We investigated whether growth and activity of fungi under drought conditions were structured by trade-offs among traits in 15 fungal isolates from a Mediterranean Southern California grassland. We inoculated fungi onto sterilized litter that was incubated at three moisture levels (4, 27, and 50% water holding capacity, WHC). For each isolate, we characterized traits that described three potential lifestyles within the newly proposed “YAS” framework: growth yield, resource acquisition, and stress tolerance. Specifically, we measured fungal hyphal length per unit litter decomposition for growth yield; the potential activities of the extracellular enzymes cellobiohydrolase (CBH), -glucosidase (BG), -xylosidase (BX), and N-acetyl---glucosaminidase (NAG) for resource acquisition; and ability to grow in drought vs. higher moisture levels for drought stress tolerance. Although, we had hypothesized that evolutionary and physiological trade-offs would elicit negative relationships among traits, we found no supporting evidence for this hypothesis. Across isolates, growth yield, drought stress tolerance, and extracellular enzyme activities were not significantly related to each other. Thus, it is possible that drought-induced shifts in fungal community composition may not necessarily lead to changes in fungal biomass or decomposer ability in this arid grassland.

Invasive Acacia Tree Species Affect Instream Litter Decomposition Through Changes in Water Nitrogen Concentration and Litter Characteristics.

Non-native nitrogen-fixing Acacia species have been invading riparian ecosystems worldwide, potentially threatening stream communities that strongly depend on allochthonous litter. We examined the effects of the invasion of native deciduous temperate forests by Acacia species on litter decomposition and associated fungal decomposers in streams. Litter of native (Alnus glutinosa and Quercus robur) and invasive (Acacia melanoxylon) species were enclosed in fine-mesh bags and immersed in three native and three invaded streams, for 14-98 days. Litter decomposition rates, fungal biomass, and aquatic hyphomycete sporulation rates were higher in invaded than in native streams, likely due to the higher water nitrogen concentration found in invaded streams. Alnus glutinosa litter had higher aquatic hyphomycete sporulation rates and species richness, and higher decomposition rates, probably because they were soft and nitrogen rich. Quercus robur litter also had high aquatic hyphomycete sporulation rates but lower decomposition rates than Al. glutinosa, probably due to high polyphenol concentration and carbon:nitrogen ratio. Acacia melanoxylon litter had lower aquatic hyphomycete sporulation rates and species richness, and lower decomposition rates, most likely because it was very tough. Thus, litter decomposition rates varied in the order: Al. glutinosa > Q. robur > Ac. melanoxylon. The aquatic hyphomycete community structure strongly differed between native and invaded streams, and among litter species, suggesting that microbes were sensitive to water nitrogen concentration and litter characteristics. Overall, increases in water nitrogen concentration and alterations in litter characteristics promoted by the invasion of native riparian forests by Acacia species may affect the activity and community structure of microbial decomposers, and instream litter decomposition, thus altering the functioning of stream ecosystems.

Diversity, distribution, and xerophilic tolerance of cultivable fungi associated with the Antarctic angiosperms

We characterized the diversity, distribution, systematic colonization, and xerophilic capabilities of fungi associated with the Antarctic angiosperms Colobanthus quitensis and Deschampsia antarctica collected at different sites of the South Shetlands Islands, Antarctic Peninsula. A total of 684 fungal isolates were obtained and identified into 67 taxa from 32 genera. The highest fungal diversity and richness were obtained from the rhizosphere, roots, and leaves, in order, and only 11 taxa shared between both plants. Penicillium and Pseudogymnoascus were the dominant fungal genera. However, the rarefaction curves for plant fungal assemblages did not reach a plateau, suggesting that these Antarctic plants may host more fungi in their tissues and rhizospheres. A total of 460 isolates grew at water activity (aw) = 0.95, 200 at 0.90, 110 at 0.81, and 47 at 0.66. Antarctomyces, Cladosporium, Mortierella, Leptosphaeria, Penicillium, Pseudogymnoascus, and Thelebolus taxa grew at aw = 0.81 and 0.66 and considered highly xerophilic. In addition, specific isolates of Penicillium and Thelebolus exhibited the highest mycelial growth at aw = 0.66. Our results show that the internal tissues and rhizosphere of Antarctic angiosperms host rich and diverse fungal communities dominated by cold-adapted and endemic taxa, which seem to coexist as symbionts and decomposer fungi. In addition, specific fungi are able to colonize different parts of the plant, suggesting a high ecological relationship with their hosts. Finally, different fungi living in the rhizosphere displayed remarkable xerophilic tolerance, representing promising candidates for further biotechnological studies, including identification of genes for applications in industry and agriculture.

Inhibitory effects of climate change on the growth and extracellular enzyme activities of a widespread Antarctic soil fungus.

Temperatures approaching or exceeding 20°C have been measured during summer in polar regions at the surfaces of barren fellfield soils under cloudless skies around solar noon. However, despite the upper temperature limit for the growth of cold‐adapted microbes—which are abundant in polar soils and have pivotal roles in nutrient cycling—typically being close to this temperature, previous studies have not addressed the consequences of climate change for the metabolism of these organisms in the natural environment. Here in a 5‐year field experiment on Alexander Island in the southern maritime Antarctic, we show that the abundance of Pseudogymnoascus roseus, the most widespread decomposer fungus in maritime Antarctic fellfield soils, is reduced by 1–2 orders of magnitude when irrigated and nutrient‐amended soils are warmed to >20°C during summer. Laboratory experiments under conditions mimicking those during midsummer in the natural environment indicated that the hyphal extension rates of P. roseus isolates and the activities of five extracellular enzymes are reduced by 54%–96% at high water availability after exposure to temperatures cycling daily from 2 to 21°C and 2 to 24°C, relative to temperatures cycling from 2 to 18°C. Given that the temperatures of surface soils at the study site already reach 19°C during midsummer, the observations reported here suggest that, at predicted rates of warming arising from moderate greenhouse gas emissions, inhibitory effects of climate change on the metabolism of P. roseus could manifest themselves within the next few decades. Furthermore, with peak temperatures at the surfaces of fellfield soils at other maritime Antarctic locations and in High Arctic and alpine regions already exceeding 20°C during summer, the observations suggest that climate warming has the potential to inhibit the growth of other cold‐adapted microbes, with negative effects on soils as the Earth's climate continues to warm.

The potentials of biochar from agricultural waste as a carrier material of biofertilizer for swamplands

Biochar has pores suitable for microbial habitat, and it contains carbon which can be used as an energy source by microbes. The research aims to determine the potential of some biochar as a carrier of biological fertilizer for swamplands. The treatment given was the type of biochar (rice husk, coconut shell, and palm empty fruit bunches) and the microbial type ie decomposer, Phosphate Solubilizing Bacteria (PSB), N Fixing Bacteria, and a consortium microbial. The design used was a Factorial Complete Randomized Design, 3 replications. Biochar analysis included organic C, total N, pH, CEC, SiO2, ash content and water content. Calculation of microbial populations was done at 2, 6 and 10 weeks after inoculation. Biochar rice husks, oil palm empty fruit bunches and coconut shells were very effective as decomposer carrier material. The highest of population of N-fixing bacteria and PSB at 6 weeks after inoculation was in the biochar rice husk reached 0.33 x 106 cfu/g for N-fixing bacteria and 54.8 x 106 cfu/g for P solvent bacterial. Rice husk biochar can be used as a carrier material both for a single biofertilizer, as well as a consortium biofertilizer that consists of decomposer fungi, P solubilizing bacteria and N-fixing bacteria.

Fungal assemblages in predictive stream bioassessment: A cross-taxon comparison along multiple stressor gradients

Degradation of freshwater ecosystems requires efficient tools for assessing the ecological status of freshwater biota and identifying potential cause(s) for their biological degradation. While diatoms and macroinvertebrates are widely used in stream bioassessment, the potential utility of microbial communities has not been fully harnessed. Using data from 113 Finnish streams, we assessed the performance of aquatic leaf-associated fungal decomposers, relative to benthic macroinvertebrates and diatoms, in modelling-based bioassessment. We built multi-taxon niche -type predictive models for fungal assemblages by using genus-based and sequence-based identification levels. We then compared the models’ precision and accuracy in the prediction of reference conditions (number of native taxa) to corresponding models for macroinvertebrates and diatoms. Genus-based fungal model nearly equalled the accuracy and precision of our best model (macroinvertebrates), whereas the sequence-based model was less accurate and tended to overestimate the number of taxa. However, when the models were applied to streams disturbed by anthropogenic stressors (nutrient enrichment, sedimentation and acidification), alone or in combination, the sequence-based fungal assemblages were more sensitive than other taxonomic groups, especially when multiple stressors were present. Microbial leaf decomposition rates were elevated in sediment-stressed streams whereas decomposition attributable to leaf-shredding macroinvertebrates was accelerated by nutrients and decelerated by sedimentation. Comparison of leaf decomposition results to model output suggested that leaf decomposition rates do not detect effectively the presence of multiple simultaneous disturbances. The rapid development of global microbial database may soon enable species-level identification of leaf-associated fungi, facilitating a more precise and accurate modelling of reference conditions in streams using fungal communities. This development, combined with the sensitivity of aquatic fungi in detecting the presence of multiple human disturbances, makes leaf-associated fungal assemblages an indispensable addition in a stream ecologist’s toolbox.

Isolation of Efficient Cellulose Decomposer in Sandy Cropland and Its Application in Straw Turnover in Agro-Pasture Ecotone of Northern China

Slow organic material and nutrient turnover is one of the limiting processes in arid and semi-arid ecosystems, and cellulose decomposers play important role in straw turnover and nutrient return in cropland ecosystem in drylands. In order to moderate the limiting effect of material turnover, a high efficient cellulose decomposing fungus was screened from 85 cellulose decomposing fungi and we named the isolated fugus as NMCel-crop1 in the sandy cropland of Horqin Sandy Land in a semi-arid agro-pasture ecotone in northern China. This fungal decomposer was identified as Rhizomucor variabilis by using morphological and rDNA-ITS molecular methods. The optimized temperature for expressing its CMC (carboxymethyl cellulose) enzyme activity ranges from 40-55 °C. The CMC enzyme activity was significantly and highly produced by the NMCel-crop1 than that in situ soil in the cropland, and the filter paper decomposition rate was 82% in 7 days. The field straw decomposition experiment showed that the decomposition rate of maize straw infected by NMCel-crop1 reached at 92.5% in one year, which was 26% higher than that without infection. Straw turnover accelerated by NMCel-crop1 significantly increased soil organic carbon (SOC) and total nitrogen (TN) by 34.08% and 14.26%, respectively, indicating that the selected high efficient decomposing fungus could accelerate straw turnover rate, and increase soil organic carbon and nitrogen content and promote soil fertility and soil health in the sandy cropland, as well as potentially improve crop productivity and quality in the sustainable agriculture management of the arid and semi-arid sandy cropland.

Characteristics of fungal community structure during the decomposition of mixed foliage litter from Pinus massoniana and broadleaved tree species in southwestern China

AbstractAimsThe conifer litter is fairly recalcitrant and nutrient poor, and broadleaved litter promotes coniferous litter decomposition by increasing degradable nutrients and promoting microbial metabolism. Mixing Pinus massoniana litter and three broadleaved litters may increase the diversity and abundance of fungal decomposers compared with those in P. massoniana litter and vary depending on the number and proportion of broadleaved species included.MethodsWe analysed the composition and diversity of fungal communities during mixed litter decomposition in southwestern China with 35 treatments (P. massoniana, Toona sinensis, Cinnamomum camphora and Sassafras tzumu litter) using Illumina high-throughput sequencing.Important FindingsThe mixed litters increased fungal diversity and richness compared with those in the single-species litter, except in the following treatments: P. massoniana litter accounting for 70%–80% in the P. massoniana + T. sinensis, P. massoniana + S. tzumu + T. sinensis and P. massoniana + S. tzumu + C. camphora combinations, and P. massoniana + S. tzumu + C. camphora + T. sinensis combination with small proportion of T. sinensis litter. The diversity and richness of the 7:1:2 combination of P. massoniana + C. camphora + T. sinensis were significantly higher than those in the other treatments. Ascomycota and Basidiomycota were the dominant phyla, and Aspergillus was the most abundant genus. The decomposition of litters from one needleleaf and one broadleaved species (6:4) and one needleleaf species and two broadleaved species (broadleaved litter accounting for 30%–40%) exhibited synergistic interactions throughout the decomposition process, and the relative abundance of fungi that decompose refractory substances increased. The P. massoniana + C. camphora + T. sinensis combination and a 30%–40% broadleaf litter proportion increased fungal diversity and accelerated the decomposition of recalcitrant coniferous litter. Therefore, C. camphora and T. sinensis are a potential candidate species for mixed planting with P. massoniana.

Using Wood Rot Phenotypes to Illuminate the "Gray" Among Decomposer Fungi.

Wood-decomposing fungi use distinct strategies to deconstruct wood that can significantly vary carbon release rates and fates. White and brown rot-type fungi attack lignin as a prerequisite to access carbohydrates (white rot) or selectively remove carbohydrates (brown rot). Soft rot fungi use less well-studied mechanisms to deconstruct wood (e.g., cavitation and erosion). These fungi often co-exist in nature, creating a balance in carbon turnover that could presumably “tip” in a changing climate. There is no simple genetic marker, however, to distinguish fungi by rot types, and traditional black and white distinctions (brown and white, in this case) cannot explain a spectrum of “gray” carbon loss possibilities. In this study, we tested 39 wood-degrading fungal strains along this spectrum of rot types. We tracked wood mass loss and chemical changes in aspen blocks in early- to mid-decay stages, including three signatures of fungal nutritional mode measured from wood rather than from fungus: dilute alkali solubility, water-soluble monosaccharides, and lignin loss (%) relative to density loss (%) (L/D). Results were then plotted relative to rot types and correlated with gene counts, combining new data with past results in some cases. Results yielded a novel distinction in soluble monosaccharide patterns for brown rot fungi, and reliable distinctions between white and brown rot fungi, although soft rot fungi were not as clearly distinguished as suggested in past studies. Gene contents (carbohydrate-active enzymes and peroxidases) also clearly distinguished brown and white rot fungi, but did not offer reliable correlation with lignin vs. carbohydrate selectivity. These results support the use of wood residue chemistry to link fungal genes (with known or unknown function) with emergent patterns of decomposition. Wood signatures, particularly L/D, not only confirm the rot type of dominant fungi, but they offer a more nuanced, continuous variable to which we can correlate genomic, transcriptomic, and secretomic evidence rather than limit it to functional categories as distinct “bins.”

Soil texture and straw type modulate the chemical structure of residues during four-year decomposition by regulating bacterial and fungal communities

The changes of chemical structure and decomposer community during straw degradation have been inconsistent in previous reports, showing either convergence or divergence of chemical structures or microbial communities among different straw types. Hence the strength of their relationship remains unclear. Here, we directly measured the chemical structures and bacterial and fungal communities of wheat (Triticum aestivum L.) and maize (Zea mays L.) residues after four-year decomposition in three Calcaric Fluvisols that varied in soil textures. Separation of the chemical structures among the six soil-straw combinations (two straw types × three soil textures) were generally coupled with trends in the communities of bacterial and fungal decomposers, but the nature of their coupling differed. In the sand soil, soil texture was the central feature that shaped bacterial and fungal communities for both straw types, driving in turn the convergence of chemical structures of both decomposing straws. In contrast, in the sandy loam and silty clay soils, straw type was the primary regulator of the colonizing bacterial and fungal communities, which resulted in the divergence of chemical structures according to straw type.

Composition and Diversity of Fungal Decomposers of Submerged Wood in Two Lakes in the Brazilian Amazon State of Pará

Aquatic ecosystems in tropical forests have a high diversity of microorganisms, including fungi, which are important decomposers of submerged wood. Despite the importance of their role in decomposition, research concerning the diversity of freshwater fungi from Brazilian Amazonian environments is scarce. The aim of this work was to describe the composition and diversity of fungi present on submerged wood in two lakes of the Brazilian Amazon (State of Pará). Fragments of decaying wood (30 samples per lake) were collected from the Lakes Juá and Maicá. The wood samples were inspected for 6 months in the presence of fungal reproductive structures. Fungi observed in the wood were identified morphologically. Twenty-three taxa were identified in the Lake Juá (10 sexual and 13 asexual) and 26 taxa in the Lake Maicá (17 sexual, 9 asexual). ITS sequences were obtained for 14 taxa to aid in identification. In the Lakes Juá and Maicá, the diversity indices were H': 2.6514 and H': 2.8174, respectively. The Sørensen index of the fungal communities in the studied lakes was 0.3673. This study is the first to describe the fungal biodiversity of two important aquatic environments in Pará, Brazil.

Cultivable fungi associated with bryosphere of bipolar mosses Polytrichastrum alpinum and Polytrichum juniperinum in King George Island, South Shetland Islands, Maritime Antarctica

We characterized the diversity of cultivable fungal assemblages associated with the bryospheres of the bipolar mosses Polytrichastrum alpinum and Polytrichastrum juniperinum resident in King George Island, South Shetland Islands, Maritime Antarctica. From different parts of the mosses, 160 fungal isolates were obtained and identified using molecular biology methods as 43 taxa of 28 distinct genera. Antarctomyces psychrotrophicus, Mrakia gelida, Pseudogymnoascus sp., Melanodiplodia sp., and Vishniacozyma victoriae were the dominant taxa and displayed the highest values of frequency. Ecological diversity indices showed that the fungal assemblages were high but ranged among the mosses. Fungi of the bryospheres of both mosses showed different colonization patterns. Only A. psychrotrophicus, M. gelida, Pseudogymnoascus sp., and Leotiomycetidae sp. occurred as endophytes, epiphytes, and in the rhizoidosphere of P. alpinum. In contrast, the bryosphere of P. juniperinum did not show a single common fungus across its different portions. Our results show that the bryosphere of the bipolar Antarctic mosses seem to represent an interesting hostspot of fungal diversity dominated by cosmopolitan cold-adapted and endemic species recognized as symbionts and decomposer species. The high fungal diversity detected suggests that the Antarctic mosses may offer a protected microhabitat (bryosphere) favorable for the survival, dispersal, and colonization of symbionts and decomposer fungi in the different extreme environments of Antarctica.

Fungal communities in decomposing wood along an energy wood harvest gradient

The current requirements to decrease the consumption and greenhouse gas emissions of fossil fuels have increased the demand of renewable energy sources. In forestry, this situation has intensified harvesting practices resulting in a decreased amount of woody debris left on the clear-cut areas. Impacts of energy wood harvest on wood-decomposing fungi were studied in a large-scale experiment in clear-cut stands in three geographical areas in Finland. A sequence of treatments was expected to form a forestry induced soil disturbance gradient: (1) logging residues left at site, no soil preparation; (2) logging residues left at site, patch mounding; (3) 70% logging residue removal, patch mounding; and (4) complete stump and logging residue removal, patch mounding. Pre-weighed wood discs were incubated on the intact soil cover for four years to estimate decomposition rate and fungal decomposer community. A soil sample was taken underneath each disc to evaluate the direct inoculation potential of the soil. The main results were as follows: (1) The differences between the treatments were not significant, while the geographical factors affected the decomposition rate and the fungal communities of the wood discs. (2) The fungal composition in the wood discs did not reflect the underlying soil fungal community, which indicates that a part of the fungal species inhabiting wood discs originated from airborne surrounding sources. (3) The increase in fungal species diversity was associated to the wood decay process, indicated by parallel increase in the wood decomposition rate and the number of white rot and mycorrhizal fungi. Thus our study indicates that in addition to local environment, landscape-level factors control the decomposer fungal community and its activity in wood.

Functional convergence in the decomposition of fungal necromass in soil and wood.

Understanding the post-senescent fate of fungal mycelium is critical to accurately quantifying forest carbon and nutrient cycling, but how this organic matter source decomposes in wood remains poorly studied. In this study, we compared the decomposition of dead fungal biomass (a.k.a. necromass) of two species, Mortierella elongata and Meliniomyces bicolor, in paired wood and soil plots in a boreal forest in northern Minnesota, USA. Mass loss was quantified at four time points over an 8-week incubation and the richness and composition of the fungal communities colonizing fungal necromass were characterized using high-throughput sequencing. We found that the structure of fungal decomposer communities in wood and soil differed, but, in both habitats, there was relatively rapid decay (∼30% remaining after 56 days). Mass loss was significantly faster in soil and for high-quality (i.e. high nitrogen and low melanin) fungal necromass. In both habitats, there was a clear trajectory of early colonization by opportunistic fungal taxa followed by colonization of fungi with greater enzymatic capacities to degrade more recalcitrant compounds, including white-rot and ectomycorrhizal fungi. Collectively, our results indicate that patterns emerging regarding substrate quality effects on fungal necromass decomposition in soil and leaf litter can be largely extended to fungal necromass decomposition in wood.

Effects of mixed-species litter on bacterial and fungal lignocellulose degradation functions during litter decomposition

Lignocellulose is the main component of forest litter. Due to the recalcitrance of coniferous litter, nutrient turnover is usually slower in coniferous plantations. Lignocellulose decomposition is reportedly rapid in mixed-species litter, but the underlying microbial metabolic pathways that may explain this rapid rate are not well-studied. We collected litter at 60, 150, 270, and 360 days after leaf fall at three plantation types: larch, sassafras, and larch/sassafras mixed plantations. We investigated the contents of lignocellulose components, enzyme activities, microbial communities, and potential genetic functional pathways related to lignocellulose degradation. Most rates of lignocellulose component degradation and enzyme activities in mixed litter during decomposition were significantly higher than in larch litter. The relative abundances of Betaproteobacteria and Dothideomycetes, which are involved in lignocellulose degradation, were significantly higher in mixed-species litter than in larch litter. Bacterial cellulose and hemicellulose, and fungal lignin degradation genes were significantly influenced by plantation forest type. Mantel tests showed that (i) the content of lignocellulose significantly correlated with bacterial and fungal community composition and enzyme activities, and (ii) fungal decomposers might be the main drivers of lignocellulose degradation in different litter types. Mixing larch and sassafras litter changed the composition of the microbial community and the lignocellulose-degradation gene complement, accelerated the decomposition of lignocelluloses, and restored soil quality.