Frequent fire reorganizes fungal communities and slows decomposition across a heterogeneous pine savanna landscape

Smut fungus (Langdonia walkerae) incidence is lower in two bunchgrass species (Aristida stricta and A. beyrichiana) after fires early in the year

PREMISE

In frequently burned southeastern USA pine-grassland communities, wiregrass (Aristida stricta and A. beyrichiana) are dominant bunchgrasses whose flowers are infected during flowering by a smut fungus (Langdonia walkerae). We hypothesized that because prescribed fire timing affects wiregrass flowering patterns, it could affect smut incidence (occurrence of smut on plants) and severity of infection in inflorescences and spikelets. Because soil order could influence plant susceptibility, we hypothesized that these patterns would differ between soil orders. We hypothesized differences between species as representative of geographic variation in this ecosystem.

METHODS

We surveyed the incidence and severity of L. walkerae in wiregrass populations (85 populations at 14 sites) that had been prescription burned at different times during the previous year. We used binomial regressions to test whether incidence and severity differed by burn day, soil order, or species, with site as a random effect.

RESULTS

Fires that occurred in the winter were associated with significantly lower incidence than fires later in the year (as the months progressed into summer). Plants growing on Spodosol soils were significantly less likely to be infected than those on other soils. More variation in incidence, however, was explained by site, suggesting that site-specific characteristics were important. Smut severity in inflorescences and spikelets was greater overall in populations of A. stricta than in southern populations (A. beyrichiana).

CONCLUSIONS

Our findings indicate that fire timing and soil order affect L. walkerae incidence in wiregrass plants, but neither appears to be associated with greater severity. Patterns of smut infection are related to site history and geographic variation.

Prescribed fire selects for a pyrophilous soil sub-community in a northern California mixed conifer forest

Prescribed fire is a critical strategy for mitigating the effects of catastrophic wildfires. While the above-ground response to fire has been well-documented, fewer studies have addressed the effect of prescribed fire on soil microorganisms. To understand how soil microbial communities respond to prescribed fire, we sampled four plots at a high temporal resolution (two burned, two controls), for 17 months, in a mixed conifer forest in northern California, USA. Using amplicon sequencing, we found that prescribed fire significantly altered both fungal and bacterial community structure. We found that most differentially abundant fungal taxa had a positive fold-change, while differentially abundant bacterial taxa generally had a negative fold-change. We tested the null hypothesis that these communities assembled due to neutral processes (i.e., drift and/or dispersal), finding that >90% of taxa fit this neutral prediction. However, a dynamic sub-community composed of burn-associated indicator taxa that were positively differentially abundant was enriched for non-neutral amplicon sequence variants, suggesting assembly via deterministic processes. In synthesizing these results, we identified 15 pyrophilous taxa with a significant and positive response to prescribed burns. Together, these results lay the foundation for building a process-driven understanding of microbial community assembly in the context of the classical disturbance regime of fire.

Fire shapes fungal guild diversity and composition through direct and indirect pathways

Fire has shaped global ecosystems for millennia by directly killing organisms and indirectly altering habitats and resources. All terrestrial ecosystems, including fire-prone ecosystems, rely on soil-inhabiting fungi, where they play vital roles in ecological processes. Yet our understanding of how fire regimes influence soil fungi remains limited and our knowledge of these interactions in semiarid landscapes is virtually absent. We collected soil samples and vegetation measurements from sites across a gradient in time-since-fire ages (0-75 years-since-fire) and fire frequency (burnt 0-5 times during the recent 29-year period) in a semiarid heathland of south-eastern Australia. We characterized fungal communities using ITS amplicon-sequencing and assigned fungi taxonomically to trophic guilds. We used structural equation models to examine direct, indirect and total effects of time-since-fire and fire frequency on total fungal, ectomycorrhizal, saprotrophic and pathogenic richness. We used multivariate analyses to investigate how total fungal, ectomycorrhizal, saprotrophic and pathogenic species composition differed between post-fire successional stages and fire frequency classes. Time-since-fire was an important driver of saprotrophic richness; directly, saprotrophic richness increased with time-since-fire, and indirectly, saprotrophic richness declined with time-since-fire (resulting in a positive total effect), mediated through the impact of fire on substrates. Frequently burnt sites had lower numbers of saprotrophic and pathogenic species. Post-fire successional stages and fire frequency classes were characterized by distinct fungal communities, with large differences in ectomycorrhizal species composition. Understanding the complex responses of fungal communities to fire can be improved by exploring how the effects of fire flow through ecosystems. Diverse fire histories may be important for maintaining the functional diversity of fungi in semiarid regions.

Co-responses of bacterial and fungal communities to fire management treatments in Mediterranean pyrophytic ecosystems

Cistus scrublands are pyrophytic ecosystems and occur widely across Mediterranean regions. Management of these scrublands is critical to prevent major disturbances, such as recurring wildfires. This is because management appears to compromise the synergies necessary for forest health and the provision of ecosystem services. Furthermore, it supports high microbial diversity, opening questions of how forest management practices impact belowground associated diversity as research related to this issue is scarce. This study aims to investigate the effects of different fire prevention treatments and site history on bacterial and fungi co-response and co-occurrence patterns over a fire-risky scrubland ecosystem. Two different site histories were studied by applying three different fire prevention treatments and samples were analyzed by amplification and sequencing of ITS2 and 16S rDNA for fungi and bacteria, respectively. The data revealed that site history, especially regarding fire occurrence, strongly influenced the microbial community. Young burnt areas tended to have a more homogeneous and lower microbial diversity, suggesting environmental filtering to a heat-resistant community. In comparison, young clearing history also showed a significant impact on the fungal community but not on the bacteria. Some bacteria genera were efficient predictors of fungal diversity and richness. For instance, Ktedonobacter and Desertibacter were a predictor of the presence of the edible mycorrhizal bolete Boletus edulis. These results demonstrate fungal and bacterial community co-response to fire prevention treatments and provide new tools for forecasting forest management impacts on microbial communities.

Pyrophilic Plants Respond to Postfire Soil Conditions in a Frequently Burned Longleaf Pine Savanna

AbstractFire-plant feedbacks engineer recurrent fires in pyrophilic ecosystems like savannas. The mechanisms sustaining these feedbacks may be related to plant adaptations that trigger rapid responses to fire's effects on soil. Plants adapted for high fire frequencies should quickly regrow, flower, and produce seeds that mature rapidly and disperse postfire. We hypothesized that the offspring of such plants would germinate and grow rapidly, responding to fire-generated changes in soil nutrients and biota. We conducted an experiment using longleaf pine savanna plants that were paired on the basis of differences in reproduction and survival under annual ("more" pyrophilic) versus less frequent ("less" pyrophilic) fire regimes. Seeds were planted in different soil inoculations from experimental fires of varying severity. The more pyrophilic species displayed high germination rates followed by species-specific rapid growth responses to soil location and fire severity effects on soils. In contrast, the less pyrophilic species had lower germination rates that were not responsive to soil treatments. This suggests that rapid germination and growth constitute adaptations to frequent fires and that plants respond differently to fire severity effects on soil abiotic factors and microbes. Furthermore, variable plant responses to postfire soils may influence plant community diversity and fire-fuel feedbacks in pyrophilic ecosystems.

Unaltered fungal community after fire prevention treatments over widespread Mediterranean rockroses (Halimium lasianthum)

Mediterranean ecosystems are frequently invaded by pyrophytic scrubs such as Halimium lasianthum that colonize areas traditionally used by livestock. A diverse fungal community is associated with this kind of vegetation, playing an important ecological role in these ecosystems. However, uncontrolled expansion of these shrubs considerably increases the risk of wildfires in these stands and, hence, fire-prevention treatments are needed. To investigate the long-term effects of two different forest-fire-prevention treatments on the soil fungal community, we analyzed these communities 9 years after prescribed burning or mechanical shredding were carried out in scrubland dominated by H. lasianthum. Neither of the fire-prevention treatments had a negative long-term effect on the abundance or richness of ectomycorrhizal fungi. However, saprotrophs and lichenized fungi experienced negative effects. Soil fertility significantly affected the distribution of fungi according to their functional groups, and pH was the most influential variable in terms of the distribution of edible species. Our findings indicate that forest management practices to prevent forest fires does not negatively affect the fungal community in the long-term, but for lichens and decomposers. Moreover, prescribed burning is suggested as a more economical way of reducing the risk of wildfires without affecting the ecology of the fungal community.

Rapid bacterial and fungal successional dynamics in first year after chaparral wildfire

The rise in wildfire frequency and severity across the globe has increased interest in secondary succession. However, despite the role of soil microbial communities in controlling biogeochemical cycling and their role in the regeneration of post-fire vegetation, the lack of measurements immediately post-fire and at high temporal resolution has limited understanding of microbial secondary succession. To fill this knowledge gap, we sampled soils at 17, 25, 34, 67, 95, 131, 187, 286, and 376 days after a southern California wildfire in fire-adapted chaparral shrublands. We assessed bacterial and fungal biomass with qPCR of 16S and 18S and richness and composition with Illumina MiSeq sequencing of 16S and ITS2 amplicons. Fire severely reduced bacterial biomass by 47%, bacterial richness by 46%, fungal biomass by 86%, and fungal richness by 68%. The burned bacterial and fungal communities experienced rapid succession, with 5-6 compositional turnover periods. Analogous to plants, turnover was driven by "fire-loving" pyrophilous microbes, many of which have been previously found in forests worldwide and changed markedly in abundance over time. Fungal secondary succession was initiated by the Basidiomycete yeast Geminibasidium, which traded off against the filamentous Ascomycetes Pyronema, Aspergillus, and Penicillium. For bacteria, the Proteobacteria Massilia dominated all year, but the Firmicute Bacillus and Proteobacteria Noviherbaspirillum increased in abundance over time. Our high-resolution temporal sampling allowed us to capture post-fire microbial secondary successional dynamics and suggest that putative tradeoffs in thermotolerance, colonization, and competition among dominant pyrophilous microbes control microbial succession with possible implications for ecosystem function.

Substrate and low intensity fires influence bacterial communities in longleaf pine savanna

Bacterial communities associated with vegetation-soil interfaces have important roles in terrestrial ecosystems. These bacterial communities, studied almost exclusively in unburnt ecosystems or those affected by rare, high-intensity wildfires, have been understudied in fire-frequented grasslands and savannas. The composition of ground-level bacterial communities was explored in an old-growth pine savanna with a centuries-long management history of prescribed fires every 1-2 years. Using 16S metabarcoding, hypotheses were tested regarding differences in bacterial families of litter and soil surface substrates in patches of ground layer vegetation that were naturally burnt or unburnt during landscape-level prescribed fires. Litter/soil substrates and fire/no fire treatments explained 67.5% of bacterial community variation and differences, driven by relative abundance shifts of specific bacterial families. Fires did not strongly affect plant or soil variables, which were not linked to bacterial community differences. Litter/soil substrates and the naturally patchy frequent fires appear to generate microhabitat heterogeneity in this pine savanna, driving responses of bacterial families. Prescribed fire management may benefit from considering how fire-altered substrate heterogeneity influences and maintains microbial diversity and function, especially in these fiery ecosystems. Frequent, low-intensity fires appear ecologically important in maintaining the diverse microbial foundation that underlie ecosystem processes and services in fire-frequented habitats.

Multifarious Responses of Forest Soil Microbial Community Toward Climate Change

Forest soils are a pressing subject of worldwide research owing to the several roles of forests such as carbon sinks. Currently, the living soil ecosystem has become dreadful as a consequence of several anthropogenic activities including climate change. Climate change continues to transform the living soil ecosystem as well as the soil microbiome of planet Earth. The majority of studies have aimed to decipher the role of forest soil bacteria and fungi to understand and predict the impact of climate change on soil microbiome community structure and their ecosystem in the environment. In forest soils, microorganisms live in diverse habitats with specific behavior, comprising bulk soil, rhizosphere, litter, and deadwood habitats, where their communities are influenced by biotic interactions and nutrient accessibility. Soil microbiome also drives multiple crucial steps in the nutrient biogeochemical cycles (carbon, nitrogen, phosphorous, and sulfur cycles). Soil microbes help in the nitrogen cycle through nitrogen fixation during the nitrogen cycle and maintain the concentration of nitrogen in the atmosphere. Soil microorganisms in forest soils respond to various effects of climate change, for instance, global warming, elevated level of CO₂, drought, anthropogenic nitrogen deposition, increased precipitation, and flood. As the major burning issue of the globe, researchers are facing the major challenges to study soil microbiome. This review sheds light on the current scenario of knowledge about the effect of climate change on living soil ecosystems in various climate-sensitive soil ecosystems and the consequences for vegetation-soil-climate feedbacks.

Pine savanna restoration on agricultural landscapes: The path back to native savanna ecosystem services

Restoration of savanna ecosystems within their historic range is expected to increase provision of ecosystem services to resident human populations. However, the benefits of restoration depend on the degree to which ecosystems and their services can be restored, the rate of restoration of particular services, and tradeoffs in services between restored ecosystems and other common land uses. We use a chronosequence approach to infer multi-decadal changes in ecosystem services under management aimed at restoring fire-dependent pine savannas, including the use of frequent prescribed fire, following abandonment of row-crop agriculture in the southeastern U.S. We compare ecosystem services between restored pine savannas of different ages and reference pine savannas as well as other common land uses (row-crop agriculture, improved pasture, pine plantation, unmanaged forest). Our results suggest that restoring pine savannas results in many improvements to ecosystem services, including increases in plant species richness, perennial grass cover, tree biomass, total ecosystem carbon, soil carbon and C:N, reductions in soil bulk density and predicted erosion and sedimentation, shifts from soil fungal pathogens to fungal symbionts, and changes in soil chemistry toward reference pine savanna conditions. However, the rate of improvement varies widely among services from a few years to decades. Compared to row-crop agriculture and improved pasture, restored savannas have lower erosion, soil bulk density, and soil pathogens and a higher percentage of mycorrhizal fungi and ecosystem carbon storage. Compared to pine plantations and unmanaged forests, restored pine savannas have lower fire-prone fuel loads and higher water yield and bee pollinator abundance. Our results indicate that restoration of pine savanna using frequent fire provides a broad suite of ecosystem services that increase the landscape's overall resilience to climate change. These results are likely relevant to other savannas dominated by perennial vegetation and maintained with frequent fire.

Fire as a driver of fungal diversity - A synthesis of current knowledge

Fires occur in most terrestrial ecosystems where they drive changes in the traits, composition, and diversity of fungal communities. Fires range from rare, stand-replacing wildfires to frequent, prescribed fires used to mimic natural fire regimes. Fire regime factors, including burn severity, fire intensity, and timing, vary widely and likely determine how fungi respond to fires. Despite the importance of fungi to post-fire plant communities and ecosystem functioning, attempts to identify common fungal responses and their major drivers are lacking. This synthesis addresses this knowledge gap and ranges from fire adaptations of specific fungi to succession and assembly fungal communities as they respond to spatially heterogenous burning within the landscape. Fires impact fungi directly and indirectly through their effects on fungal survival, substrate and habitat modifications, changes in environmental conditions, and/or physiological responses of the hosts with which fungi interact. Some specific pyrophilous, or "fire-loving," fungi often appear after fire. Our synthesis explores whether such taxa can be considered cosmopolitan, and whether they are truly fire-adapted or simply opportunists adapted to rapidly occupy substrates and habitats made available by fires. We also discuss the possible inoculum sources of post-fire fungi and explore existing conceptual models and ecological frameworks that may be useful in generalizing fungal fire responses. We conclude with identifying research gaps and areas that may best transform the current knowledge and understanding of fungal responses to fire.

Current Insight into Traditional and Modern Methods in Fungal Diversity Estimates

Fungi are an important and diverse component in various ecosystems. The methods to identify different fungi are an important step in any mycological study. Classical methods of fungal identification, which rely mainly on morphological characteristics and modern use of DNA based molecular techniques, have proven to be very helpful to explore their taxonomic identity. In the present compilation, we provide detailed information on estimates of fungi provided by different mycologistsover time. Along with this, a comprehensive analysis of the importance of classical and molecular methods is also presented. In orderto understand the utility of genus and species specific markers in fungal identification, a polyphasic approach to investigate various fungi is also presented in this paper. An account of the study of various fungi based on culture-based and cultureindependent methods is also provided here to understand the development and significance of both approaches. The available information on classical and modern methods compiled in this study revealed that the DNA based molecular studies are still scant, and more studies are required to achieve the accurate estimation of fungi present on earth.

Transition from Fire-Dependent Open Forests: Alternative Ecosystem States in the Southeastern United States

Land use and fire exclusion have influenced ecosystems worldwide, resulting in alternative ecosystem states. Here, I provide two examples from the southeastern United States of fire-dependent open pine and pine-oak forest loss and examine dynamics of the replacement forests, given continued long-term declines in foundation longleaf (Pinus palustris) and shortleaf (Pinus echinata) pines and recent increases in commercial loblolly (Pinus taeda) and slash (Pinus elliottii var. elliottii) pines. Shortleaf pine-oak forest historically may have been dominant on about 32 to 38 million ha, a provisional estimate based on historical composition of 75% of all trees, and has decreased to about 2.5 million ha currently; shortleaf pine now is 3% of all trees in the northern province. Longleaf pine forest decreased from about 30 million ha, totaling 75% of all trees, to 1.3 million ha and 3% of all trees in contemporary forests of the southern province. The initial transition from open pine ecosystems to closed forests, primarily comprised of broadleaf species, was countered by conversion to loblolly and slash pine plantations. Loblolly pine now accounts for 37% of all trees. Loss of fire-dependent ecosystems and their foundation tree species affect associated biodiversity, or the species that succeed under fire disturbance.

Effects of prescribed fire frequency on wildfire emissions and carbon sequestration in a fire adapted ecosystem using a comprehensive carbon model

Prescribed fire to reduce forest fuels has been routinely applied to reduce wildfire risk in many parts of the world. It has also been proposed that prescribed fire can be used to mitigate greenhouse gas (GHG) emissions. Although prescribed fire creates emissions, if the treatment also decreases the incidence of subsequent wildfires, it is possible for the net outcome to be an emissions decline. Previous studies have suggested prescribed fire, at the frequencies required to materially impact wildfire occurrence, generally leads to net emissions increases. A focus on emissions means any change in carbon storage within the ecosystem remains unaccounted for; because living, dead, and soil carbon pools are characterized by different residence times, a re-distribution of carbon amongst these pools may either reduce or increase long-term ecosystem carbon stores. A full ecosystem carbon model has been developed to investigate the implications of prescribed fire management on total Net Ecosystem Carbon Balance (NECB), inclusive of both emissions and carbon storage. Consistent with previous work, the results suggested limited potential for reducing net GHG emissions through applying prescribed fire, with higher emissions from prescribed fire approximately offset by lower emissions and avoided carbon losses from the subsequent reduction in wildfire frequency. For example, shortening the prescribed fire interval from 25 to 10 years resulted in a NECB sequestration that was typically less than ±0.4 Mg C ha^-1 yr^-1, or less than approximately 0.1% of the total ecosystem carbon storage. Hence, whilst there was limited opportunity for achieving emission abatement outcomes from changing prescribed fire management, there were no significant emission penalties for doing so. These results suggest land managers should be free to adopt prescribed fire regimes to target specific management outcomes, without significantly impacting net emissions or total ecosystem carbon storage over the long term.

Disruption of Traditional Grazing and Fire Regimes Shape the Fungal Endophyte Assemblages of the Tall-Grass Brachypodium rupestre

The plant microbiome is likely to play a key role in the resilience of communities to the global climate change. This research analyses the culturable fungal mycobiota of Brachypodium rupestre across a sharp gradient of disturbance caused by an intense, anthropogenic fire regime. This factor has dramatic consequences for the community composition and diversity of high-altitude grasslands in the Pyrenees. Plants were sampled at six sites, and the fungal assemblages of shoots, rhizomes, and roots were characterized by culture-dependent techniques. Compared to other co-occurring grasses, B. rupestre hosted a poorer mycobiome which consisted of many rare species and a few core species that differed between aerial and belowground tissues. Recurrent burnings did not affect the diversity of the endophyte assemblages, but the percentages of infection of two core species -Omnidemptus graminis and Lachnum sp. -increased significantly. The patterns observed might be explained by (1) the capacity to survive in belowground tissues during winter and rapidly spread to the shoots when the grass starts its spring growth (O. graminis), and (2) the location in belowground tissues and its resistance to stress (Lachnum sp.). Future work should address whether the enhanced taxa have a role in the expansive success of B. rupestre in these anthropized environments.

Fungal community structure and seasonal trajectories respond similarly to fire across pyrophilic ecosystems

Fire alters microbial community composition, and is expected to increase in frequency due to climate change. Testing whether microbes in different ecosystems will respond similarly to increased fire disturbance is difficult though, because fires are often unpredictable and hard to manage. Fire recurrent or pyrophilic ecosystems, however, may be useful models for testing the effects of frequent disturbance on microbes. We hypothesized that across pyrophilic ecosystems, fire would drive similar alterations to fungal communities, including altering seasonal community dynamics. We tested fire's effects on fungal communities in two pyrophilic ecosystems, a longleaf pine savanna and tallgrass prairie. Fire caused similar fungal community shifts, including (i) driving immediate changes that favored taxa able to survive fire and take advantage of post-fire environments and (ii) altering seasonal trajectories due to fire-associated changes to soil nutrient availability. This suggests that fire has predictable effects on fungal community structure and intra-annual community dynamics in pyrophilic ecosystems, and that these changes could significantly alter fungal function. Parallel fire responses in these key microbes may also suggest that recurrent fires drive convergent changes across ecosystems, including less fire-frequented systems that may start burning more often due to climate change.

Contrasting fungal responses to wildfire across different ecosystem types

Wildfire affects our planet's biogeochemistry both by burning biomass and by driving changes in ecological communities and landcover. Some plants and ecosystem types are threatened by increasing fire pressure while others respond positively to fire, growing in local and regional abundance when it occurs regularly. However, quantifying total ecosystem response to fire demands consideration of impacts not only on aboveground vegetation, but also on soil microbes like fungi, which influence decomposition and nutrient mineralization. If fire-resistant soil fungal communities co-occur with similarly adapted plants, these above- and belowground ecosystem components should shift and recover in relative synchrony after burning. If not, fire might decouple ecosystem processes governed by these different communities, affecting total functioning. Here, we use a natural experiment to test whether fire-dependent ecosystems host unique, fire-resistant fungal communities. We surveyed burned and unburned areas across two California ecosystem types with differing fire ecologies in the immediate aftermath of a wildfire, finding that the soil fungal communities of fire-dependent oak woodlands differ from those of neighbouring mixed evergreen forests. We discovered furthermore that the latter are more strongly altered compositionally by fire than the former, suggesting that differences in fungal community structure support divergent community responses to fire across ecosystems. Our results thus indicate that fire-dependent ecosystems may host fire-resistant fungal communities.

Classifying Large Wildfires in the United States by Land Cover

Fire is an ecological process that also has socio-economic effects. To learn more about fire occurrence, I examined relationships between land classes and about 12,000 spatially delineated large wildfires (defined here as uncontrolled fires ≥200 ha, although definitions vary) during 1999 to 2017 in the conterminous United States. Using random forests, extreme gradient boosting, and c5.0 classifiers, I modeled all fires, first years (1999 to 2002), last years (2014 to 2017), the eastern, central, and western United States and seven ecoregions. The three classifiers performed well (true positive rates 0.82 to 0.94) at modeling all fires and fires by year, region, and ecoregion. The random forests classifier did not predict to other time intervals or regions as well as other classifiers and models were not constant in time and space. For example, the eastern region overpredicted fires in the western region and models for the western region underpredicted fires in the eastern region. Overall, greater abundance of herbaceous grasslands, or herbaceous wetlands in the eastern region, and evergreen forest and low abundance of crops and pasture characterized most large fires, even with regional differences. The 14 states in the northeastern United States with no or few large fires contained limited herbaceous area and abundant crops or developed lands. Herbaceous vegetation was the most important variable for fire occurrences in the western region. Lack of crops was most important for fires in the central region and a lack of pasture, crops, and developed open space was most important for fires in the eastern region. A combination of wildlands vegetation was most influential for most ecoregions, although herbaceous vegetation alone and lack of pasture, crops, and developed open space also were influential. Despite departure from historical fire regimes, these models demonstrated that herbaceous vegetation remains necessary for fires and that evergreen forests in particular are fire-prone, while reduction of vegetation surrounding housing developments will help provide a buffer to reduce large fires.

Frequent fire slows microbial decomposition of newly deposited fine fuels in a pyrophilic ecosystem

Frequent fires maintain nearly 50% of terrestrial ecosystems, and drive ecosystem changes that govern future fires. Since fires are dependent on available plant or fine fuels, ecosystem processes that alter fine fuel loads like microbial decomposition are particularly important and could modify future fires. We hypothesized that variation in short-term fire history would influence fuel dynamics in such ecosystems. We predicted that frequent fires within a short-time period would slow microbial decomposition of new fine fuels. We expected that fire effects would differ based on dominant substrates and that fire history would also alter soil nutrient availability, indirectly slowing decomposition. We measured decomposition of newly deposited fine fuels in a Longleaf pine savanna, comparing plots that burned 0, 1, 2, or 3 times between 2014 and 2016, and which were located in either close proximity to or away from overstory pines (Longleaf pine, Pinus palustris). Microbial decomposition was slower in plots near longleaf pines and, as the numbers of fires increased, decomposition slowed. We then used structural equation modeling to assess pathways for these effects (number of fires, 2016 fuel/fire characteristics, and soil chemistry). Increased fire frequency was directly associated with decreased microbial decomposition. While increased fires decreased nutrient availability, changes in nutrients were not associated with decomposition. Our findings indicate that increasing numbers of fires over short-time intervals can slow microbial decomposition of newly deposited fine fuels. This could favor fine fuel accumulation and drive positive feedbacks on future fires.

GlobalFungi, a global database of fungal occurrences from high-throughput-sequencing metabarcoding studies

Fungi are key players in vital ecosystem services, spanning carbon cycling, decomposition, symbiotic associations with cultivated and wild plants and pathogenicity. The high importance of fungi in ecosystem processes contrasts with the incompleteness of our understanding of the patterns of fungal biogeography and the environmental factors that drive those patterns. To reduce this gap of knowledge, we collected and validated data published on the composition of soil fungal communities in terrestrial environments including soil and plant-associated habitats and made them publicly accessible through a user interface at https://globalfungi.com . The GlobalFungi database contains over 600 million observations of fungal sequences across > 17 000 samples with geographical locations and additional metadata contained in 178 original studies with millions of unique nucleotide sequences (sequence variants) of the fungal internal transcribed spacers (ITS) 1 and 2 representing fungal species and genera. The study represents the most comprehensive atlas of global fungal distribution, and it is framed in such a way that third-party data addition is possible.

On the Three Major Recycling Pathways in Terrestrial Ecosystems

Plants are the largest biomass component of most terrestrial ecosystems, and litter decomposition is considered the dominant process by which nutrients return to plants. We show that in terrestrial ecosystems, there are three major pathways by which plant biomass is degraded into forms that release nutrients again available to plants: microbial decomposition; vertebrate herbivory; and wildfires. These processes act at different spatial and temporal scales, have different niches, and generates different ecological and evolutionary feedbacks. This holistic view in which microbes, herbivores, and wildfires play a joint role in the functioning of ecosystems contributes to a better understanding of the diversity of mechanisms regulating the biosphere.