Belowground community responses to fire: meta-analysis reveals contrasting responses of soil microorganisms and mesofauna

A global meta-analysis reveals a consistent reduction of soil fauna abundance and richness as a consequence of land use conversion

Land use conversion of natural to production systems is one of the most important threats to belowground communities and to the key ecosystem processes in which they are involved. Available literature shows positive, negative, and neutral effects of land use changes on soil fauna communities; and these varying effects may be due to different characteristics of natural and production systems and soil organisms. We hypothesize that land conversion from high to low plant biomass, diversity, and structural complexity systems may have the most negative impacts on soil fauna. Here, we performed the first meta-analysis evaluating the overall effects of land use conversion on soil invertebrate communities and the influence of factors related to characteristics of natural and production systems, of soil fauna communities and methods. We compiled a dataset of 260 publications that yielded 1732 observations for soil fauna abundance and 459 for richness. Both abundance and richness showed a global decline as a consequence of natural land conversion to production systems. These negative effects were stronger, in general, when the conversion occurred in tropical and subtropical sites, and when natural systems were replaced by croplands, pastures and grazing systems. The effects of land use conversion also depended on soil property changes. In addition, the abundance of most taxa and richness of Acari and Collembola were strongly reduced by land use changes while Annelida were not affected. The highest reduction in abundance was recorded in omnivores and predators, whereas detritivores showed a reduction in richness. Our meta-analysis shows consistent evidence of soil biodiversity decline due to different land use changes and the partial dependence of those effects on the magnitude of changes in vegetation. These findings stress the need to continue developing production modes that effectively preserve soil biodiversity and ecosystem processes, without hampering food production.

Immediate Impacts of Wildfires on Ground-dwelling macroinvertebrate Communities under Stones in Mediterranean Oak Forests

Wildfires are considered a major disturbance to forest ecosystems in the Mediterranean countries of Southern Europe. Although ground-dwelling macroinvertebrates are crucial to many soil functions, there is a fundamental lack of understanding of how wildfires impact this community in the immediate term and of the role of stones in their survival. Hence, in the present study we assessed the immediate effects of wildfires in the ground-dwelling macroinvertebrate community found under stones by comparing communities in burnt and non-burnt Mediterranean oak forests. Our results revealed that stones allowed the survival of many taxa in the burnt area. However, abundance, richness, diversity, and equitability per stone were significantly lower at the burnt than unburnt sites. Furthermore, the results also showed that richness and abundance increased significantly with increasing stone depth and area, both at the burnt and unburnt sites. Significant changes at the trophic level were observed in the burnt area comparing to the unburnt, particularly a decline in predators. No significant differences were identified concerning habitat associations among taxa. Overall, this study stressed the role of stones as microhabitats and refuge for the ground-dwelling macroinvertebrate community during wildfires.

Global changes and their environmental stressors have a significant impact on soil biodiversity-A meta-analysis

Identifying the main threats to soil biodiversity is crucial as soils harbor ∼60% of global biodiversity. Many previous meta-analyses investigating the impact of different global changes (GCs) on biodiversity have omitted soil fauna or are limited by the GCs studied. We conducted a broad-scale meta-analysis focused on soil fauna communities, analyzing 3,161 effect sizes from 624 publications studying climate change, land-use intensification, pollution, nutrient enrichment, invasive species and habitat fragmentation. Land-use intensification resulted in large reductions in soil fauna communities, especially for the larger-bodied groups. Unexpectedly, pollution caused the largest negative impact on soil biodiversity - particularly worrying due to continually increasing levels of pollution and poor mechanistic understanding of impacts relative to other GCs. Not all GCs and stressors were detrimental; organic-based nutrient enrichment often resulted in positive responses. Including soil biodiversity in large-scale analyses is vital to fully understand the impact of GCs across the different realms.

Biochar alters the soil fauna functional traits and community diversity: A quantitative and cascading perspective

With the widespread use of biochar, the cascading effects of biochar exposure on soil fauna urgently require deeper understanding. A meta-analysis quantified hierarchical changes in functional traits and community diversity of soil fauna under biochar exposure. Antioxidant enzymes (24.1 %) did not fully mitigate the impact of MDA (13.5 %), leading to excessive DNA damage in soil fauna (21.2 %). Concurrently, reproduction, growth, and survival rates decreased by 20.2 %, 8.5 %, and 21.2 %, respectively. Due to a 39.7 % increase in avoidance behavior of soil fauna towards biochar, species richness ultimately increased by 80.2 %. Compared to other feeding habits, biochar posed a greater threat to the survival of herbivores. Additionally, macrofauna were the most sensitive to biochar. The response of soil fauna also depended on the type, size, concentration, and duration of biochar exposure. It should be emphasized that as exposure concentration increased, the damage to soil fauna became more severe. Furthermore, the smaller the biochar sizes, the greater the damage to soil fauna. To mitigate the adverse effects on soil fauna, this study recommens applying biochar at appropriate times and selecting large sizes in low to medium concentrations. These findings confirm the threat of biochar to soil health from the perspective of soil fauna.

Metal nanoparticles and pesticides under global climate change: Assessing the combined effects of multiple abiotic stressors on soil microbial ecosystems

The soil is a vital resource that hosts many microorganisms crucial in biogeochemical cycles and ecosystem health. However, human activities such as the use of metal nanoparticles (MNPs), pesticides and the impacts of global climate change (GCCh) can significantly affect soil microbial communities (SMC). For many years, pesticides and, more recently, nanoparticles have contributed to sustainable agriculture to ensure continuous food production to sustain the significant growth of the world population and, therefore, the demand for food. Pesticides have a recognized pest control capacity. On the other hand, nanoparticles have demonstrated a high ability to improve water and nutrient retention, promote plant growth, and control pests. However, it has been reported that their accumulation in agricultural soils can also adversely affect the environment and soil microbial health. In addition, climate change, with its variations in temperature and extreme water conditions, can lead to drought and increased soil salinity, modifying both soil conditions and the composition and function of microbial communities. Abiotic stressors can interact and synergistically or additively affect soil microorganisms, significantly impacting soil functioning and the capacity to provide ecosystem services. Therefore, this work reviewed the current scientific literature to understand how multiple stressors interact and affect the SMC. In addition, the importance of molecular tools such as metagenomics, metatranscriptomics, proteomics, or metabolomics in the study of the responses of SMC to exposure to multiple abiotic stressors was examined. Future research directions were also proposed, focusing on exploring the complex interactions between stressors and their long-term effects and developing strategies for sustainable soil management. These efforts will contribute to the preservation of soil health and the promotion of sustainable agricultural practices.

Post-fire recovery of nematode communities along a slope gradient in a pine forest

We investigated the enduring consequences of a wildfire on nematode diversity and abundance in a pine forest, employing a slope gradient approach. Our primary objective was to determine the extent of post-fire alterations in the nematode community 3 years after the incident, to understand if the ecosystem has returned to its pre-fire state or has transitioned to a distinctive ecological environment. Three distinct burned pine forest sites at varying elevations were sampled to capture short-scale soil property variations due to slope gradients, while unburned forest sites served as controls. A consistent pattern emerged where the lowest altitude sites exhibited the highest nematode abundances, although still lower than unburned sites. Fire-induced changes were profound, shifting from fungivore dominance in unburned sites to bacterivore and herbivore dominance in burned sites. Alterations in soil properties post-fire, particularly reduced organic matter and nitrogen content, were closely associated with nematode community shifts. Water availability played a crucial role with lower moisture levels at higher elevations impacting nematode populations. Structural differences in the nematode community primarily resulted from fire disturbance rather than altitude. This study emphasizes the persistent and transformative impact of wildfire on nematode communities, highlighting the intricate interplay between ecological disturbances, soil properties, and nematode trophic dynamics.

Wildfire Impacts on Molecular Changes of Dissolved Organic Matter during Its Passage through Soil

The frequency and intensity of global wildfires are escalating, leading to an increase in derived pyrogenic dissolved organic matter (pyDOM), which potentially influences the riverine carbon reservoir and poses risks to drinking water safety. However, changes in pyDOM properties as it traverses through soil to water bodies are highly understudied due to the challenges of simulating such processes under laboratory conditions. In this study, we extracted soil DOM along hillslope gradients and soil depths in both burned and unburned catchments post wildfire. Using high-resolution mass spectrometry and a substrate-explicit model, we observed significant increases in the relative abundance of condensed aromatics (ConAC) and tannins in wildfire-affected soil DOM. Wildfire-affected soil DOM also displayed a broader spectrum of molecular and thermodynamic properties, indicative of its diverse composition and reactivity. Furthermore, as the fire-induced weakening of topsoil microbial reprocessing abilities hindered the transformation of plant-derived DOM, the relative abundance of lignin-like compounds increased with soil depth in the fire regions. Meanwhile, the distribution of shared molecular formulas along the hillslope gradient (from shoulder to toeslope) exhibited analogous patterns in both burned and unburned catchments. Although there was an increased prevalence of ConAC and tannin in the burned catchments, the relative abundance of these fractions diminished along the hillslope in all three catchments. Based on the substrate-explicit model, the biodegradability exhibited by wildfire-affected DOM fractions offers the possibility of its conversion along hillslopes. Our findings reveal the spatial distribution of DOM properties after a wildfire, facilitating accurate evaluation of dissolved organic carbon composition involved in the watershed-scale carbon cycle.

Restoration age affects microbial-herbaceous plant interactions in an oak woodland

In degraded ecosystems, soil microbial communities (SMCs) may influence the outcomes of ecological restoration. Restoration practices can affect SMCs, though it is unclear how variation in the onset of restoration activities in woodlands affects SMCs, how those SMCs influence the performance of hard-to-establish woodland forbs, and how different woodland forbs shape SMCs. In this study, we quantified soil properties and species abundances in an oak woodland restoration chronosequence (young, intermediate, and old restorations). We measured the growth of three woodland forb species when inoculated with live whole-soil from young, intermediate, or old restorations. We used DNA metabarcoding to characterize SMCs of each inoculum treatment and the soil after conditioning by each plant species. Our goals were to (1) understand how time since the onset of restoration affected soil abiotic properties, plant communities, and SMCs in a restoration chronosequence, (2) test growth responses of three forb species to whole-soil inoculum from restoration sites, and (3) characterize changes in SMCs before and after conditioning by each forb species. Younger restored woodlands had greater fire-sensitive tree species and lower concentrations of soil phosphorous than intermediate or older restored woodlands. Bacterial and fungal soil communities varied significantly among sites. Forbs exhibited the greatest growth in soil from the young restoration. Each forb species developed a unique soil microbial community. Our results highlight how restoration practices affect SMCs, which can in turn affect the growth of hard-to-establish forb species. Our results also highlight that the choice of forb species can alter SMCs, which could have long-term potential consequences for restoration success.

Unraveling the impact of wildfires on permafrost ecosystems: Vulnerability, implications, and management strategies

Permafrost regions play an important role in global carbon and nitrogen cycling, storing enormous amounts of organic carbon and preserving a delicate balance of nutrient dynamics. However, the increasing frequency and severity of wildfires in these regions pose significant challenges to the stability of these ecosystems. This review examines the effects of fire on chemical, biological, and physical properties of permafrost regions. The physical, chemical, and pedological properties of frozen soil are impacted by fires, leading to changes in soil structure, porosity, and hydrological functioning. The combustion of organic matter during fires releases carbon and nitrogen, contributing to greenhouse gas emissions and nutrient loss. Understanding the interactions between fire severity, ecosystem processes, and the implications for permafrost regions is crucial for predicting the impacts of wildfires and developing effective strategies for ecosystem protection and agricultural productivity in frozen soils. By synthesizing available knowledge and research findings, this review enhances our understanding of fire severity's implications for permafrost ecosystems and offers insights into effective fire management strategies.

Meta-analysis reveals that the effects of precipitation change on soil and litter fauna in forests depend on body size

Anthropogenic climate change is altering precipitation regimes at a global scale. While precipitation changes have been linked to changes in the abundance and diversity of soil and litter invertebrate fauna in forests, general trends have remained elusive due to mixed results from primary studies. We used a meta-analysis based on 430 comparisons from 38 primary studies to address associated knowledge gaps, (i) quantifying impacts of precipitation change on forest soil and litter fauna abundance and diversity, (ii) exploring reasons for variation in impacts and (iii) examining biases affecting the realism and accuracy of experimental studies. Precipitation reductions led to a decrease of 39% in soil and litter fauna abundance, with a 35% increase in abundance under precipitation increases, while diversity impacts were smaller. A statistical model containing an interaction between body size and the magnitude of precipitation change showed that mesofauna (e.g. mites, collembola) responded most to changes in precipitation. Changes in taxonomic richness were related solely to the magnitude of precipitation change. Our results suggest that body size is related to the ability of a taxon to survive under drought conditions, or to benefit from high precipitation. We also found that most experiments manipulated precipitation in a way that aligns better with predicted extreme climatic events than with predicted average annual changes in precipitation and that the experimental plots used in experiments were likely too small to accurately capture changes for mobile taxa. The relationship between body size and response to precipitation found here has far-reaching implications for our ability to predict future responses of soil biodiversity to climate change and will help to produce more realistic mechanistic soil models which aim to simulate the responses of soils to global change.

Drought legacy interacts with wildfire to alter soil microbial communities in a Mediterranean climate-type forest

Mediterranean forest ecosystems will be increasingly affected by hotter drought and more frequent and severe wildfire events in the future. However, little is known about the longer-term responses of these forests to multiple disturbances and the forests' capacity to maintain ecosystem function. This is particularly so for below-ground organisms, which have received less attention than those above-ground, despite their essential contributions to forest function. We investigated rhizosphere microbial communities in a resprouting Eucalyptus marginata forest, southwestern Australia, that had experienced a severe wildfire four years previously, and a hotter drought eight years previously. Our aim was to understand how microbial communities are affected over longer-term trajectories by hotter drought and wildfire, singularly, and in combination. Fungal and bacterial DNA was extracted from soil samples, amplified, and subjected to high throughput sequencing. Richness, diversity, composition, and putative functional groups were then examined. We found a monotonic decrease in fungal, but not bacterial, richness and diversity with increasing disturbance with the greatest changes resulting from the combination of drought and wildfire. Overall fungal and bacterial community composition reflected a stronger effect of fire than drought, but the combination of both produced the greatest number of indicator taxa for fungi, and a significant negative effect on the abundance of several fungal functional groups. Key mycorrhizal fungi, fungal saprotrophs and fungal pathogens were found at lower proportions in sites affected by drought plus wildfire. Wildfire had a positive effect on bacterial hydrogen and bacterial nitrogen recyclers. Fungal community composition was positively correlated with live tree height. These results suggest that microbial communities, in particular key fungal functional groups, are highly responsive to wildfire following drought. Thus, a legacy of past climate conditions such as hotter drought can be important for mediating the responses of soil microbial communities to subsequent disturbance like wildfire.

Fire Impacts on the Soil Metabolome and Organic Matter Biodegradability

Global wildfire activity has increased since the 1970s and is projected to intensify throughout the 21st century. Wildfires change the composition and biodegradability of soil organic matter (SOM) which contains nutrients that fuel microbial metabolism. Though persistent forms of SOM often increase postfire, the response of more biodegradable SOM remains unclear. Here we simulated severe wildfires through a controlled "pyrocosm" approach to identify biodegradable sources of SOM and characterize the soil metabolome immediately postfire. Using microbial amplicon (16S/ITS) sequencing and gas chromatography-mass spectrometry, heterotrophic microbes (Actinobacteria, Firmicutes, and Protobacteria) and specific metabolites (glycine, protocatechuate, citric cycle intermediates) were enriched in burned soils, indicating that burned soils contain a variety of substrates that support microbial metabolism. Molecular formulas assigned by 21 T Fourier transform ion cyclotron resonance mass spectrometry showed that SOM in burned soil was lower in molecular weight and featured 20 to 43% more nitrogen-containing molecular formulas than unburned soil. We also measured higher water extractable organic carbon concentrations and higher CO2 efflux in burned soils. The observed enrichment of biodegradable SOM and microbial heterotrophs demonstrates the resilience of these soils to severe burning, providing important implications for postfire soil microbial and plant recolonization and ecosystem recovery.

Effect of fire and post-fire management on soil microbial communities in a lower subtropical forest ecosystem after a mountain fire

Wildfires and post-fire management exert profound effects on soil properties and microbial communities in forest ecosystems. Understanding microbial community recovery from fire and what the best post-fire management should be is very important but needs to be sufficiently studied. In light of these gaps in our understanding, this study aimed to assess the short-term effects of wildfire and post-fire management on both bacteria and fungi community composition, diversity, structure, and co-occurrence networks, and to identify the principal determinants of soil processes influencing the restoration of these communities. Specifically, we investigated soil bacterial and fungal community composition, diversity, structure, and co-occurrence networks in lower subtropical forests during a short-term (<3 years) post-fire recovery period at four main sites in Guangdong Province, southern China. Our results revealed significant effects of wildfires on fungal community composition, diversity, and co-occurrence patterns. Network analysis indicated reduced bacterial network complexity and connectivity post-fire, while the same features were enhanced in fungal networks. However, post-fire management effects on microbial communities were negligible. Bacterial diversity correlated positively with soil microbial biomass nitrogen, soil organic carbon, and soil total nitrogen. Conversely, based on the best random forest model, fungal community dynamics were negatively linked to nitrate-nitrogen and soil water content. Spearman's correlation analysis suggested positive associations between bacterial networks and soil factors, whereas fungal networks exhibited predominantly negative associations. This study elucidates the pivotal role of post-fire management in shaping ecological outcomes. Additionally, it accentuates the discernible distinctions between bacterial and fungal responses to fire throughout a short-term recovery period. These findings contribute novel insights that bear significance in evaluating the efficacy of environmental management strategies.

Elevated methane flux in a tropical peatland post-fire is linked to depth-dependent changes in peat microbiome assembly

Fires in tropical peatlands extend to depth, transforming them from carbon sinks into methane sources and severely limit forest recovery. Peat microbiomes influence carbon transformations and forest recovery, yet our understanding of microbiome shifts post-fire is currently limited. Our previous study highlighted altered relationships between the peat surface, water table, aboveground vegetation, and methane flux after fire in a tropical peatland. Here, we link these changes to post-fire shifts in peat microbiome composition and assembly processes across depth. We report kingdom-specific and depth-dependent shifts in alpha diversity post-fire, with large differences at deeper depths. Conversely, we found shifts in microbiome composition across all depths. Compositional shifts extended to functional groups involved in methane turnover, with methanogens enriched and methanotrophs depleted at mid and deeper depths. Finally, we show that community shifts at deeper depths result from homogeneous selection associated with post-fire changes in hydrology and aboveground vegetation. Collectively, our findings provide a biological basis for previously reported methane fluxes after fire and offer new insights into depth-dependent shifts in microbiome assembly processes, which ultimately underlie ecosystem function predictability and ecosystem recovery.

Contrasting immediate impact of prescribed fires and experimental summer fires on soil organic matter quality and microbial properties in the forest floor and mineral soil in Mediterranean black pine forest

Prescribed fire (PB) is used to achieve ecological objectives and to reduce fuel hazard thus limiting detrimental impacts of wildfire and appropriate selection of prescription window is critical for these goals. Operational use of PB in the Mediterranean forest is scarce and information about its effects on soil remains incomplete. This study for the first time i) compared the immediate impact of spring and autumn PB and experimental summer fire on key properties of forest floor and mineral topsoil in Mediterranean black pine forest, and ii) assessed the capacity of PB to reduce fuel, with limited immediate impacts on soil. PB significantly reduced the 32.5 % of pre-fire forest floor depth, while summer fire consumed 88.5 % and exposed about 30 % of the mineral soil surface. Mean maximum temperature during fire at the mineral soil surface was 23 °C in PB, in contrast to 128 °C in summer fire, while soil heating at 2 cm depth was negligible in both cases. PB did not cause immediate changes in OM quality parameters, and chemical (C and N concentrations, C/N and pH) and microbiological properties (Cmic, Cmic/C, and β-glucosidase, acid phosphatase and alkaline phosphatase activities) in forest floor or mineral topsoil (0-2 cm). By contrast, summer fire greatly increased OM recalcitrance and reduced Cmic, Cmic/C and enzyme activities in forest floor immediately after fire. In the mineral topsoil, only microbial properties were significantly reduced. The maximum temperature reached during fire in forest floor and topsoil was associated with most of the overall changes in properties in both layers. The findings suggest that prescribed fire can significantly reduce fuel with limited initial impacts on soil. Although these findings are encouraging for operational use of prescribed burning in the ecosystem under study, long-term monitoring of repeated application of the technique on soil properties and other ecosystem components is necessary.

High resilience of soil bacterial communities to large wildfires with an important stochastic component

Wildfires alter the structure and functioning of ecosystems through changes in their biotic and abiotic components. A deeper understanding recovery process concerning diverse communities and properties within these components can provide valuable insights into the ecological effects of wildfires. Therefore, it is appropriate to enhance our understanding of the resilience of bacterial communities after wildfires within Mediterranean ecosystems. In this research, soil bacterial community resilience was evaluated in three types of ecosystems for two fire severities, two years after a large wildfire in Mediterranean ecosystems. The resilience of the soil bacterial community refers to its ability to return to original state after disturbance. This capacity can be estimated by the study of its recovery over time. In this study we evaluated the resilience using the variables: alpha diversity, beta diversity and the changes in abundance of both OTUs (Operational Taxonomic Units) and principal bacterial taxa (phyla, classes or orders). Our results showed that resilience depends on fire severity and type of ecosystem. We studied three ecosystems with different stage in the secondary succession: low maturity shrublands and heathlands, and high maturity oak forests. In general, high resilience in the soil bacterial community was observed in heathlands under low and high fire severity conditions. The other two ecosystems were resilient only under low fire severity. Stochastic replacement of the abundance of the OTUs was observed in all three ecosystems, with a notable impact on oak forests, under during high-severity conditions.

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.

Testing the contribution of dispersal to microbial succession following a wildfire

IMPORTANCE

Identifying the mechanisms underlying microbial community succession is necessary for predicting how microbial communities, and their functioning, will respond to future environmental change. Dispersal is one mechanism expected to affect microbial succession, yet the difficult nature of manipulating microorganisms in the environment has limited our understanding of its contribution. Using a dispersal exclusion experiment, this study isolates the specific effect of environmental dispersal on bacterial and fungal community assembly over time following a wildfire. The work demonstrates the potential to quantify dispersal impacts on soil microbial communities over time and test how dispersal might further interact with other assembly processes in response to environmental change.

Soil arthropod community responses to restoration in areas impacted by iron mining tailings deposition after Fundão dam failure

In 2015, the failure of the Fundão dam in Mariana, Brazil released ~43 million m3 of iron mining tailings into the environment. Despite restoration initiatives in the following years, few studies-and most focused on revegetation-have evaluated the effectiveness of the restoration process in areas impacted by the disaster. We aimed to evaluate the responses of the arthropod community in areas impacted by iron mining tailings deposition from the Fundão dam that is in the restoration process. We defined sampling units in the riparian zone of the Gualaxo do Norte River, which is under restoration, and in a native not impacted riparian zone. We collected soil arthropods using pitfall traps and sampled environmental variables in the same sites. We used generalize least squares models (GLS) to test if the restored areas already presented values of arthropod diversity and functional group abundance similar to the reference area and to test which environmental variables are influencing arthropod diversity. We also tested how large the differences of arthropod community composition between the study areas and used the index of indicator species (IndVal) to verify which species could be used as an indicator of reference or restoration areas. The diversity of arthropods and the functional groups of detritivores and omnivores were higher in the native riparian zone. Understory density, soil density, organic matter content, and microbial biomass carbon were the environmental variables that significantly explained the diversity and species composition of arthropods. We show that restoration areas still have different soil arthropod diversity values and community composition when compared to reference areas. Evaluating the response of the arthropod community to the restoration process and long-term monitoring are essential to achieve a satisfactory result in this process and achieve a self-sustaining ecosystem.

Non-native and native tree species plantations and seasonality could have substantial impacts on the diversity of indigenous soil fauna in a semi-arid forest ecosystem

The temporal and spatial dynamics of soil fauna in many terrestrial ecosystems are still not fully understood, while soil fauna is one of the most critical characteristics in assessing soil quality. Therefore, the effects of native [Quercus brantii (QP) and Amygdalus scoparia (AMP)] and non-native [Cupressus arizonica (CUP) and Pinus eldarica (PIN)] plantations and natural trees [Quercus brantii coppice trees (QNC), standard (QNS), and Amygdalus scoparia (AMN)] on diversity and abundance of macro- and mesofauna were done in the semi-arid forest of Zagros, Iran. Samples were collected beneath the canopy of woody species and the outer edge of the canopy in spring and summer seasons. For this purpose, soil samples [(7 samples per woody species + control) × 2 seasons × 3 replicates] were taken from 0 to 20 cm depths. Each soil sample was a mix of three soil cores. For the macrofauna, 15 species belonging to four families (in spring) and 17 species in nine families (in summer) were collected and identified. For the soil mesofauna, 14 species belonging to 14 families (in spring) and 13 species in 13 different families (in summer) were identified, respectively. The fauna diversity indices under the canopy of studied species were higher in summer season than in spring. The result showed that the macrofauna diversity was affected by tree species, while mesofauna was affected by seasonal changes. Macrofauna biodiversity was higher under the canopy of PIN and CUP than other trees. Principle component analysis showed that the diversity of the macrofauna was higher under the canopy of PIN and CUP, and influenced by soil characteristic properties, soil properties did not influence them. Yet the diversity of the mesofauna was affected by soil characteristics and was higher in areas with higher organic carbon, nitrogen, substrate-induced respiration, basal respiration, microbial carbon biomass, and alkaline phosphatase. In addition, mesofauna biodiversity had a significant positive correlation with the soil quality index (SQI). SQI was higher under the canopy of natural stands, especially the QNS. Conservation of native species (QNS, QNC, and AMN) and plantation with native deciduous species (QP and AMP) seem to moderate environmental conditions and increase soil macro- and mesofauna diversity and SQI.

Experimentally determined traits shape bacterial community composition one and five years following wildfire

Wildfires represent major ecological disturbances, burning 2-3% of Earth's terrestrial area each year with sometimes drastic effects above- and belowground. Soil bacteria offer an ideal, yet understudied system within which to explore fundamental principles of fire ecology. To understand how wildfires restructure soil bacterial communities and alter their functioning, we sought to translate aboveground fire ecology to belowground systems by determining which microbial traits are important post-fire and whether changes in bacterial communities affect carbon cycling. We employed an uncommon approach to assigning bacterial traits, by first running three laboratory experiments to directly determine which microbes survive fires, grow quickly post-fire and/or thrive in the post-fire environment, while tracking CO2 emissions. We then quantified the abundance of taxa assigned to each trait in a large field dataset of soils one and five years after wildfires in the boreal forest of northern Canada. We found that fast-growing bacteria rapidly dominate post-fire soils but return to pre-burn relative abundances by five years post-fire. Although both fire survival and affinity for the post-fire environment were statistically significant predictors of post-fire community composition, neither are particularly influential. Our results from the incubation trials indicate that soil carbon fluxes post-wildfire are not likely limited by microbial communities, suggesting strong functional resilience. From these findings, we offer a traits-based framework of bacterial responses to wildfire.

Larger presence of ectomycorrhizae detected from pygmy pine ecotype in the fire-frequent pine barrens ecosystem

Pine barrens ecosystem has acidic, sandy, and nutrient-poor soil and is prone to drought and fire. In the New Jersey Pine Barrens, the predominant pitch pine (Pinus rigida) consists of two ecotypes: the regular pitch pines with heights of 4.6-12 m, and the pygmy pines of low stature (1.2-1.8 m) in the New Jersey Pine Plains. Previous ecological studies suggested that the dwarf pines in the Pine Plains that are embedded within the Pine Barrens were an evolutionary adaptation to frequent fire. Pines are obligate ectomycorrhizal (EcM) mutualists, and their root mycobiota may contribute to stress protection and plant health. However, information on the mycobiota associated with plants in the pine barrens ecosystem is lacking. To have a holistic understanding of the evolution and adaptation in this stressed environment, we used both culture-independent metabarcoding and culture-based method to characterize the mycobiota from soil and root of the two ecotypes and to identify core mycobiota. We found that Agaricomycetes, Leotiomycetes, and Mucoromycotina are predominant fungi in the New Jersey Pine Barrens ecosystem, which is rich in root mutualistic fungi. We observed that the pygmy pine roots had significantly higher density of EcM tips than the regular pine roots. This was corroborated by our metabarcoding analysis, which showed that the pygmy pine trees had higher ratio of ectomycorrhiza-forming fungi than the regular-statured pines. We hypothesize that symbiotrophic EcM fungi associated with pygmy pines are capable of mitigating high fire stress in the Pine Plains.

The combined effect of fire and nitrogen addition on biodiversity and herbaceous aboveground productivity in a coastal shrubland

Introduction

Fire and nitrogen (N) deposition each impact biodiversity and ecosystem productivity. However, the effect of N deposition on ecosystem recovery after fire is still far from understood, especially in coastal wetlands.

Methods

We selected a typical coastal shrubland to simulate three N deposition levels (0, 10, and 20 g N m-2 year-1) under two different burned conditions (unburned and burned) in the Yellow River Delta of North China. Soil properties, soil microbial biodiversity, shrub growth parameters, herbaceous biodiversity, and aboveground productivity were determined after experimental treatments for 1 year.

Results

We found that fire had a stronger influence on the ecosystem than N addition. One year after the fire, shrub growth had significantly decreased, while soil pH, soil electrical conductivity, herbaceous biodiversity, soil microbial biodiversity, and herbaceous aboveground productivity significantly increased. Conversely, a single year of N addition only slightly increased herbaceous aboveground productivity. The combined effect of fire and N addition was only significant for fungus biodiversity and otherwise had minimal influence. Interestingly, we found that herbaceous aboveground productivity was positively associated with fungal community diversity under unburned conditions but not in burned shrublands. Fire showed a great impact on soil parameters and biodiversity in the coastal wetland ecosystem even after a full year of recovery.

Discussion

Fire may also diminish the influence of several belowground factors on herbaceous aboveground productivity, which ultimately reduces recovery and stability. Appropriate N addition may be an effective way to improve the ecosystem productivity in a wetland dominated by shrub species.

Signatures of prescribed fire in the microbial communities of Cornus florida are largely undetectable five months post-fire

Prescribed burn is a management tool that influences the physical structure and composition of forest plant communities and their associated microorganisms. Plant-associated microorganisms aid in host plant disease tolerance and increase nutrient availability. The effects of prescribed burn on microorganisms associated with native ecologically and economically important tree species, such as Cornus florida L. (flowering dogwood), are not well understood, particularly in aboveground plant tissues (e.g., leaf, stem, and bark tissues). The objective of this study was to use 16S rRNA gene and ITS2 region sequencing to evaluate changes in bacterial and fungal communities of five different flowering dogwood-associated niches (soil, roots, bark, stem, and leaves) five months following a prescribed burn treatment. The alpha- and beta-diversity of root bacterial/archaeal communities differed significantly between prescribed burn and unburned control-treated trees. In these bacterial/archaeal root communities, we also detected a significantly higher relative abundance of sequences identified as Acidothermaceae, a family of thermophilic bacteria. No significant differences were detected between prescribed burn-treated and unburned control trees in bulk soils or bark, stem, or leaf tissues. The findings of our study suggest that prescribed burn does not significantly alter the aboveground plant-associated microbial communities of flowering dogwood trees five months following the prescribed burn application. Further studies are required to better understand the short- and long-term effects of prescribed burns on the microbial communities of forest trees.

Pathways framework identifies wildfire impacts on agriculture

Wildfires are a growing concern to society and the environment in many parts of the world. Within the United States, the land area burned by wildfires has steadily increased over the past 40 years. Agricultural land management is widely understood as a force that alters fire regimes, but less is known about how wildfires, in turn, impact the agriculture sector. Based on an extensive literature review, we identify three pathways of impact-direct, downwind and downstream-through which wildfires influence agricultural resources (soil, water, air and photosynthetically active radiation), labour (agricultural workers) and products (crops and livestock). Through our pathways framework, we highlight the complexity of wildfire-agriculture interactions and the need for collaborative, systems-oriented research to better quantify the magnitude of wildfire impacts and inform the adaptation of agricultural systems to an increasingly fire-prone future.

All boreal forest successional stages needed to maintain the full suite of soil biodiversity, community composition, and function following wildfire

Wildfire is a natural disturbance in boreal forest systems that has been predicted to increase in frequency, intensity, and extent due to climate change. Most studies tend to assess the recovery of one component of the community at a time but here we use DNA metabarcoding to simultaneously monitor soil bacteria, fungi, and arthropods along an 85-year chronosequence following wildfire in jack pine-dominated ecosites. We describe soil successional and community assembly processes to better inform sustainable forest management practices. Soil taxa showed different recovery trajectories following wildfire. Bacteria shared a large core community across stand development stages (~ 95-97% of their unique sequences) and appeared to recover relatively quickly by crown closure. By comparison fungi and arthropods shared smaller core communities (64-77% and 68-69%, respectively) and each stage appeared to support unique biodiversity. We show the importance of maintaining a mosaic ecosystem that represents each stand development stage to maintain the full suite of biodiversity in soils following wildfire, especially for fungi and arthropods. These results will provide a useful baseline for comparison when assessing the effects of human disturbance such as harvest or for assessing the effects of more frequent wildfire events due to climate change.

Fire severity as a key determinant of aboveground and belowground biological community recovery in managed even-aged boreal forests

Changes in fire regime of boreal forests in response to climate warming are expected to impact postfire recovery. However, quantitative data on how managed forests sustain and recover from recent fire disturbance are limited.Two years after a large wildfire in managed even-aged boreal forests in Sweden, we investigated how recovery of aboveground and belowground communities, that is, understory vegetation and soil microbial and faunal communities, responded to variation in the severity of soil (i.e., consumption of soil organic matter) and canopy fires (i.e., tree mortality).While fire overall enhanced diversity of understory vegetation through colonization of fire adapted plant species, it reduced the abundance and diversity of soil biota. We observed contrasting effects of tree- and soil-related fire severity on survival and recovery of understory vegetation and soil biological communities. Severe fires that killed overstory Pinus sylvestris promoted a successional stage dominated by the mosses Ceratodon purpureus and Polytrichum juniperinum, but reduced regeneration of tree seedlings and disfavored the ericaceous dwarf-shrub Vaccinium vitis-idaea and the grass Deschampsia flexuosa. Moreover, high tree mortality from fire reduced fungal biomass and changed fungal community composition, in particular that of ectomycorrhizal fungi, and reduced the fungivorous soil Oribatida. In contrast, soil-related fire severity had little impact on vegetation composition, fungal communities, and soil animals. Bacterial communities responded to both tree- and soil-related fire severity. Synthesis: Our results 2 years postfire suggest that a change in fire regime from a historically low-severity ground fire regime, with fires that mainly burns into the soil organic layer, to a stand-replacing fire regime with a high degree of tree mortality, as may be expected with climate change, is likely to impact the short-term recovery of stand structure and above- and belowground species composition of even-aged P. sylvestris boreal forests.

The pervasive impact of global climate change on plant-nematode interaction continuum

Pest profiles in today's global food production system are continually affected by climate change and extreme weather. Under varying climatic conditions, plant-parasitic nematodes (PPNs) cause substantial economic damage to a wide variety of agricultural and horticultural commodities. In parallel, their herbivory also accredit to diverse ecosystem services such as nutrient cycling, allocation and turnover of plant biomass, shaping of vegetation community, and alteration of rhizospheric microorganism consortium by modifying the root exudation pattern. Thus PPNs, together with the vast majority of free-living nematodes, act as ecological drivers. Because of direct exposure to the open environment, PPN biology and physiology are largely governed by environmental factors including temperature, precipitation, humidity, atmospheric and soil carbon dioxide level, and weather extremes. The negative effects of climate change such as global warming, elevated CO2, altered precipitation and the weather extremes including heat waves, droughts, floods, wildfires and storms greatly influence the biogeographic range, distribution, abundance, survival, fitness, reproduction, and parasitic potential of the PPNs. Changes in these biological and ecological parameters associated to the PPNs exert huge impact on agriculture. Yet, depending on how adaptable the species are according to their geo-spatial distribution, the consequences of climate change include both positive and negative effects on the PPN communities. While assorting the effects of climate change as a whole, it can be estimated that the changing environmental factors, on one hand, will aggravate the PPN damage by aiding to abundance, distribution, reproduction, generation, plant growth and reduced plant defense, but the phenomena like sex reversal, entering cryptobiosis, and reduced survival should act in counter direction. This seemingly creates a contraposition effect, where assessing any confluent trend is difficult. However, as the climate change effects will differ according to space and time it is apprehensible that the PPNs will react and adapt according to their location and species specificity. Nevertheless, the bio-ecological shifts in the PPNs will necessitate tweaking their management practices from the agri-horticultural perspective. In this regard, we must aim for a 'climate-smart' package that will take care of the food production, pest prevention and environment protection. Integrated nematode management involving precise monitoring and modeling-based studies of population dynamics in relation to climatic fluctuations with escalated reliance on biocontrol, host resistance, and other safer approaches like crop rotation, crop scheduling, cover cropping, biofumigation, use of farmyard manure (FYM) would surely prove to be viable options. Although the novel nematicidal molecules are target-specific and relatively less harmful to the environment, their application should not be promoted following the global aim to reduce pesticide usage in future agriculture. Thus, having a reliable risk assessment with scenario planning, the adaptive management strategies must be designed to cope with the impending situation and satisfy the farmers' need.

Prescribed fire alters nematode communities in an old-field grassland

Fire is a common disturbance in many biomes, with both beneficial and detrimental effects on soil biology, which largely depend on fire intensity. However, little is known about the impact of fire on soil nematode communities in terrestrial ecosystem. In the present study, we investigated the effects of short-term prescribed fire on soil nematode communities and soil properties in an old-field grassland in Northern China. The results showed that burning significantly increased soil nematode abundance by 77% and genus richness by 49% compared to the control. Burning also decreased taxon dominance by 45% (Simpson's D) and increased nematode diversity by 31% (Shannon-Weaver H'). However, burning increased plant parasites (particularly genera Cephalenchus and Pratylenchus) and shifted community to more bacterial-feeding genera (i.e., decreased Channel Index). Generally, burning increased soil bio-available nitrogen (NH4 +-N and NO3 --N) content, which would be the main drivers causing nematode community to flourish via a "bottom-up" effect. These results suggest that prescribed fire increases nematode diversity and alters community composition toward more plant parasites and bacterial feeders. Our findings highlight the importance of prescribed fire management in shaping short-term nematode community structure and function, but the long-term effects and impacts of these changes on soil nutrient and carbon cycling remain unknown.

Using simulated wildland fire to assess microbial survival at multiple depths from biocrust and bare soils

Introduction

Surface soil microbial communities are directly exposed to the heat from wildland fires. Due to this, the microbial community composition may be stratified within the soil profile with more heat tolerant microbes near the surface and less heat tolerant microbes, or mobile species found deeper in the soil. Biological soil crusts, biocrusts, are found on the soil surface and contain a diverse microbial community that is directly exposed to the heat from wildland fires.

Methods

Here, we used a simulated fire mesocosm along with a culture-based approach and molecular characterization of microbial isolates to understand the stratification of biocrust and bare soil microbes after low severity (450°C) and high severity (600°C) fires. We cultured and sequenced microbial isolates from 2 to 6 cm depth from both fire types.

Results

The isolates were stratified along the soil depth. Green algal isolates were less thermotolerant and found in the deeper depths (4–6 cm) and the control soils, while several cyanobacteria in Oscillatoriales, Synechococcales, and Nostocales were found at 2–3 cm depth for both fire temperatures. An Alphaproteobacteria isolate was common across several depths, both fire types, and both fire temperatures. Furthermore, we used RNA sequencing at three depths after the high severity fire and one control to determine what microbial community is active following a fire. The community was dominated by Gammaproteobacteria, however some Cyanobacteria ASVs were also present.

Discussion

Here we show evidence of stratification of soil and biocrust microbes after a fire and provide evidence that these microbes are able to survive the heat from the fire by living just below the soil surface. This is a steppingstone for future work on the mechanisms of microbial survival after fire and the role of soil insulation in creating resilient 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.

Post-fire forest floor succession in a Central European temperate forest depends on organic matter input from recovering vegetation rather than on pyrogenic carbon input from fire

The predicted global increase in the frequency, severity, and intensity of forest fires includes Central Europe, which is not currently considered as a wildfire hotspot. Because of this, a detailed knowledge of long-term post-fire forest floor succession is essential for understanding the role of wildfires in Central European temperate forests. In this study, we used a space-for-time substitution approach and exploited a unique opportunity to observe successional changes in the physical, chemical, and microbial properties of the forest floor in coniferous forest stands on a chronosequence up to 110 years after fire. In addition, we assessed whether the depletion of organic matter (OM) and input of pyrogenic carbon (pyC) have significant effects on the post-fire forest floor succession. The bulk density (+174 %), pH (+4 %), and dissolved phosphorus content (+500 %) increased, whereas the water holding capacity (-51 %), content of total organic carbon and total nitrogen (-50 %), total phosphorus (-40 %), dissolved organic carbon (-23 %), microbial respiration and biomass (-60 %), and the abundance of fungi (-65 %) and bacteria (-45 %) decreased shortly after the fire event and then gradually decreased or increased, respectively, relative to the pre-disturbance state. The post-fire forest floor succession was largely dependent on changes in the OM content rather than the pyC content, and thus was dependent on vegetation recovery. The time needed to recover to the pre-disturbance state was <110 years for physical and chemical properties and < 45 years for microbial properties. These times closely correspond to previous studies focusing on the recovery of forest floor properties in different climate zones, suggesting that the times needed for forest vegetation and forest floor properties to recover to the pre-disturbance state are similar across climate zones.

Contaminant pulse following wildfire is associated with shifts in estuarine benthic communities

Novel combinations of climatic conditions due to climate change and prolonged fire seasons have contributed to an increased occurrence of "megafires". Such large-scale fires pose an unknown threat to biodiversity due to the increased extent and severity of burn. Assessments of wildfires often focus on terrestrial ecosystems and effects on aquatic habitats are less documented, particularly in coastal environments. In a novel application of eDNA techniques, we assessed the impacts of the 2019-2020 Australian wildfires on the diversity of estuarine benthic sediment communities in six estuaries in NSW, Australia, before and after the fires. Estuaries differed in area of catchment burnt (0-92%) and amount of vegetative buffer that remained post-fire between burnt areas and waterways. We found greater dissimilarities in the composition and abundance of eukaryotic and bacterial sediment communities in estuaries from burnt catchments with no buffer compared to those with an intact buffer or from unburnt catchments. Shifts in composition in highly burnt catchments were associated with increased concentrations of nutrients, carbon, including fire-derived pyrogenic carbon, and copper, which was representative of multiple highly correlated trace metals. Changes in the relative abundances of certain taxonomic groups, such as sulfate-reducing and nitrifying bacterial groups, in the most impacted estuaries indicate potential consequences for the functioning of sediment communities. These results provide a unique demonstration of the use of eDNA to identify wildfire impacts on ecological communities and emphasize the importance of vegetative buffers in limiting wildfire-associated impacts.

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.

Moss biocrust accelerates the recovery and resilience of soil microbial communities in fire-affected semi-arid Mediterranean soils

After wildfires in Mediterranean ecosystems, ruderal mosses are pioneer species, stabilizing the soil surface previous to the establishment of vascular vegetation. However, little is known about the implication of pioneer moss biocrusts for the recovery and resilience of soils in early post-fire stages in semi-arid areas. Therefore, we studied the effects of the burgeoning biocrust on soil physicochemical and biochemical properties and the diversity and composition of microbial communities after a moderate-to-high wildfire severity. Seven months after the wildfire, the biocrust softened the strong impact of the fire in soils, affecting the diversity and composition of bacteria and fungi community compared to the uncrusted soils exposed to unfavourable environmental stress. Soil moisture, phosphorous, and enzyme activities representing the altered biogeochemical cycles after the fire, were the main explanatory variables for biocrust microbial community composition under the semi-arid conditions. High bacterial diversity was found in soils under mosses, while long-lasting legacies are expected in the fungal community, which showed greater sensitivity to the fire. The composition of bacterial and fungal communities at several taxonomical levels was profoundly altered by the presence of the moss biocrust, showing a rapid successional transition toward the unburned soil community. Pioneer moss biocrust play an important role improving the resilience of soil microbial communities. In the context of increasing fire intensity, studying the moss biocrust effects on the recovery of soils microbiome is essential to understanding the resistance and resilience of Mediterranean forests to wildfires.

Diversity of genomic adaptations to the post-fire environment in Pezizales fungi points to crosstalk between charcoal tolerance and sexual development

Wildfires drastically impact the soil environment, altering the soil organic matter, forming pyrolyzed compounds, and markedly reducing the diversity of microorganisms. Pyrophilous fungi, especially the species from the orders Pezizales and Agaricales, are fire-responsive fungal colonizers of post-fire soil that have historically been found fruiting on burned soil and thus may encode mechanisms of processing these compounds in their genomes. Pyrophilous fungi are diverse. In this work, we explored this diversity and sequenced six new genomes of pyrophilous Pezizales fungi isolated after the 2013 Rim Fire near Yosemite Park in California, USA: Pyronema domesticum, Pyronema omphalodes, Tricharina praecox, Geopyxis carbonaria, Morchella snyderi, and Peziza echinospora. A comparative genomics analysis revealed the enrichment of gene families involved in responses to stress and the degradation of pyrolyzed organic matter. In addition, we found that both protein sequence lengths and G + C content in the third base of codons (GC3) in pyrophilous fungi fall between those in mesophilic/nonpyrophilous and thermophilic fungi. A comparative transcriptome analysis of P. domesticum under two conditions - growing on charcoal, and during sexual development - identified modules of genes that are co-expressed in the charcoal and light-induced sexual development conditions. In addition, environmental sensors such as transcription factors STE12, LreA, LreB, VosA, and EsdC were upregulated in the charcoal condition. Taken together, these results highlight genomic adaptations of pyrophilous fungi and indicate a potential connection between charcoal tolerance and fruiting body formation in P. domesticum.

Wildfire-dependent changes in soil microbiome diversity and function

Forest soil microbiomes have crucial roles in carbon storage, biogeochemical cycling and rhizosphere processes. Wildfire season length, and the frequency and size of severe fires have increased owing to climate change. Fires affect ecosystem recovery and modify soil microbiomes and microbially mediated biogeochemical processes. To study wildfire-dependent changes in soil microbiomes, we characterized functional shifts in the soil microbiota (bacteria, fungi and viruses) across burn severity gradients (low, moderate and high severity) 1 yr post fire in coniferous forests in Colorado and Wyoming, USA. We found severity-dependent increases of Actinobacteria encoding genes for heat resistance, fast growth, and pyrogenic carbon utilization that might enhance post-fire survival. We report that increased burn severity led to the loss of ectomycorrhizal fungi and less tolerant microbial taxa. Viruses remained active in post-fire soils and probably influenced carbon cycling and biogeochemistry via turnover of biomass and ecosystem-relevant auxiliary metabolic genes. Our genome-resolved analyses link post-fire soil microbial taxonomy to functions and reveal the complexity of post-fire soil microbiome activity.

Fire frequency and type regulate the response of soil carbon cycling and storage to fire across soil depths and ecosystems: A meta-analysis

Fire is a very common disturbance in terrestrial ecosystems and can give rise to significant effects on soil carbon (C) cycling and storage. Here, we conducted a global meta-analysis on the response of soil C cycling and storage across soil profiles (organic layer, 0-5 cm, 0-10 cm, 0-20 cm, and 20-100 cm) to fire reported in 308 studies across 383 sites and examined the role of fire frequency, fire type, soil type, ecosystem type, and post-fire time in regulating the response of soil C dynamics to fire. Overall, we found soil C cycling and storage were more responsive to one fire and wildfire as compared to frequent fire and prescribed fire, respectively. Soil respiration significantly decreased by 22 ± 9% by one fire, but was not significantly affected by frequent fire across ecosystems. One fire significantly reduced soil C content in the organic, 0-10 cm, and 20-100 cm layers by 27 ± 16%, 10 ± 9%, and 33 ± 18%, respectively, while frequent fire significantly reduced soil C content at a depth of 0-5 cm and 0-20 cm by 29 ± 8% and 16 ± 12%, respectively. Soil C cycling and storage showed little response to frequent prescribed fire. In addition, the response of soil C cycling and storage varied among different soil and ecosystem types, with a stronger response being observed in forest than in grassland. Within 20 years post-fire, soil C cycling and storage tended to recover only after one fire but not after frequent fire. We also found that soil physicochemical properties and microbial communities were more responsive to one fire than frequent fire, which could indirectly affect the effects of fire on soil C cycling and storage. The results of our study have filled some critical gaps in previous meta-analyses in fire ecology.

Effects of short-interval reburns in the boreal forest on soil bacterial communities compared to long-interval reburns

Increasing fire frequency in some biomes is leading to fires burning in close succession, triggering rapid vegetation change and altering soil properties. We studied the effects of short-interval (SI) reburns on soil bacterial communities of the boreal forest of northwestern Canada using paired sites (n = 44). Both sites in each pair had burned in a recent fire; one site had burned within the previous 20 years before the recent fire (SI reburn) and the other had not. Paired sites were closely matched in prefire ecosite characteristics, prefire tree species composition, and stand structure. We hypothesized that there would be a significant effect of short vs. long fire-free intervals on community composition and that richness would not be consistently different between paired sites. We found that Blastococcus sp. was consistently enriched in SI reburns, indicating its role as a strongly ‘pyrophilous’ bacterium. Caballeronia sordidicola was consistently depleted in SI reburns. The depletion of this endophytic diazotroph raises questions about whether this is contributing to—or merely reflects—poor conifer seedling recolonization post-fire at SI reburns. While SI reburns had no significant effect on richness, dissimilarity between short- and long-interval pairs was significantly correlated with difference in soil pH, and there were small significant changes in overall community composition.

Microbial Community-Level Physiological Profiles and Genetic Prokaryotic Structure of Burned Soils Under Mediterranean Sclerophyll Forests in Central Chile

Forest fires alter soil microbial communities that are essential to support ecosystem recovery following land burning. These alterations have different responses according to soil abiotic pre- and post-fire conditions and fire severity, among others, and tend to decrease along vegetation recovery over time. Thus, understanding the effects of fires on microbial soil communities is critical to evaluate ecosystem resilience and restoration strategies in fire-prone ecosystems. We studied the state of community-level physiological profiles (CLPPs) and the prokaryotic community structure of rhizosphere and bulk soils from two fire-affected sclerophyll forests (one surveyed 17 months and the other 33 months after fire occurrence) in the Mediterranean climate zone of central Chile. Increases in catabolic activity (by average well color development of CLPPs), especially in the rhizosphere as compared with the bulk soil, were observed in the most recently affected site only. Legacy of land burning was still clearly shaping soil prokaryote community structure, as shown by quantitative PCR (qPCR) and Illumina MiSeq sequencing of the V4 region of the 16S rRNA gene, particularly in the most recent fire-affected site. The qPCR copy numbers and alpha diversity indexes (Shannon and Pielou’s evenness) of sequencing data decreased in burned soils at both locations. Beta diversity analyses showed dissimilarity of prokaryote communities at both study sites according to fire occurrence, and NO₃^– was the common variable explaining community changes for both of them. Acidobacteria and Rokubacteria phyla significantly decreased in burned soils at both locations, while Firmicutes and Actinobacteria increased. These findings provide a better understanding of the resilience of soil prokaryote communities and their physiological conditions in Mediterranean forests of central Chile following different time periods after fire, conditions that likely influence the ecological processes taking place during recovery of fire-affected ecosystems.

Soil bacterial assemblage responses to wildfire in low elevation southern California habitats

Understanding how wildfires and modification in plant assemblages interact to influence soil bacteria assemblages is a crucial step in understanding how these disturbances may influence ecosystem structure and function. Here, we resampled soil from three study sites previously surveyed in spring 2016 and 2017 and compared soil bacterial assemblages prior to and six months after (spring 2019) the 2018 Woolsey Fire in the Santa Monica Mountain National Recreation Area using Illumina sequencing of the 16S rRNA gene. All sites harbored both native California sage scrub and a non-native (grassland or forbland) habitat, allowing us to examine how fire influenced bacterial assemblages in common southern California habitats. Most results contrasted with our a-priori hypotheses: (1) richness and diversity increased following the fire, (2) heat/drought resistant and sensitive bacteria did not show consistent and differing patterns by increasing and decreasing, respectively, in relative abundance after the fire, and (3) bacterial assemblage structure was only minimally impacted by fire, with no differences being found between 2017 (pre-fire) and 2019 (post-fire) in three of the six habitats sampled. As sage scrub and non-native grasslands consistently harbored unique bacterial assemblages both before and following the fire, modifications in plant compositions will likely have legacy effects on these soils that persist even after a fire. Combined, our results demonstrate that bacterial assemblages in southern California habitats are minimally affected by fire. Because direct impacts of fire are limited, but indirect impacts, e.g., modifications in plant compositions, are significant, plant restoration efforts following a fire should strive to revegetate sage scrub areas to prevent legacy changes in bacterial composition.

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.

Fire promotes functional plant diversity and modifies soil carbon dynamics in tropical savanna

Fire is an evolutionary environmental filter in tropical savanna ecosystems altering functional diversity and associated C pools in the biosphere and fluxes between the atmosphere and biosphere. Therefore, alterations in fire regimes (e.g. fire exclusion) will strongly influence ecosystem processes and associated dynamics. In those ecosystems C dynamics and functions are underestimated by the fire-induced offset between C output and input. To determine how fire shapes ecosystem C pools and fluxes in an open savanna across recently burned and fire excluded areas, we measured the following metrics: (I) plant diversity including taxonomic (i.e. richness, evenness) and plant functional diversity (i.e. functional diversity, functional richness, functional dispersion and community weighted means); (II) structure (i.e. above- and below-ground biomass, litter accumulation); and (III) functions related to C balance (i.e. net ecosystem carbon dioxide (CO₂) exchange (NEE), ecosystem transpiration (ET), soil respiration (soil CO₂ efflux), ecosystem water use efficiency (eWUE) and total soil organic C (SOC). We found that fire promoted aboveground live and belowground biomass, including belowground organs, coarse and fine root biomass and contributed to higher biomass allocation belowground. Fire also increased both functional diversity and dispersion. NEE and total SOC were higher in burned plots compared to fire-excluded plots whereas soil respiration recorded lower values in burned areas. Both ET and eWUE were not affected by fire. Fire strongly favored functional diversity, fine root and belowground organ biomass in piecewise SEM models but the role of both functional diversity and ecosystem structure to mediate the effect of fire on ecosystem functions remain unclear. Fire regime will impact C balance, and fire exclusion may lead to lower C input in open savanna ecosystems.

Previous fire occurrence, but not fire recurrence, modulates the effect of charcoal and ash on soil C and N dynamics in Pinus pinaster Aiton forests

Understanding the effects of fire history on soil processes is key to characterise their resistance and resilience under future fire events. Wildfires produce pyrogenic carbonaceous material (PCM) that is incorporated into the soil, playing a critical role in the global carbon (C) cycle, but its interactions with soil processes are poorly understood. We evaluated if the previous occurrence of wildfires modulates the dynamic of soil C and nitrogen (N) and microbial community by soil ester linked fatty acids, after a new simulated low-medium intensity fire. Soils with a different fire history (none, one, two or three fires) were heat-shocked and amended with charcoal and/or ash derived from Pinus pinaster. Soil C and N mineralization rates were measured under controlled conditions, with burned soils showing lower values than unburned (without fire for more than sixty years). In general, no effects of fire recurrence were observed for any of the studied variables. Microbial biomass was lower in burned, with a clear dominance of Gram-positive bacteria in these soils. PCM amendments increased cumulative carbon dioxide (CO₂) production only in previously burned soils, especially when ash was added. This contrasted response to PCM between burned and unburned soils in CO₂ production could be related to the effect of the previous wildfire history on soil microorganisms. In burned soils some microorganisms might have been adapted to the resulting conditions after a new fire event. Burned soils showed a significant positive priming effect after PCM amendment, mainly ash, probably due to an increased pH and phosphorous availability. Our results reveal the role of different PCMs as drivers of C and N mineralization processes in burned soils when a new fire occurs. This is relevant for improving models that evaluate the net impact of fire in C cycling and to reduce uncertainties under future changing fire regimes scenarios.

Watershed and fire severity are stronger determinants of soil chemistry and microbiomes than within-watershed woody encroachment in a tallgrass prairie system

Fire can impact terrestrial ecosystems by changing abiotic and biotic conditions. Short fire intervals maintain grasslands and communities adapted to frequent, low-severity fires. Shrub encroachment that follows longer fire intervals accumulates fuel and can increase fire severity. This patchily distributed biomass creates mosaics of burn severities in the landscape-pyrodiversity. Afforded by a scheduled burn of a watershed protected from fires for 27 years, we investigated effects of woody encroachment and burn severity on soil chemistry and soil-inhabiting bacteria and fungi. We compared soils before and after fire within the fire-protected, shrub-encroached watershed and soils in an adjacent, annually burned and non-encroached watershed. Organic matter and nutrients accumulated in the fire-protected watershed but responded less to woody encroachment within the encroached watershed. Bioavailable nitrogen and phosphorus and fungal and bacterial communities responded to high-severity burn regardless of encroachment. Low-severity fire effects on soil nutrients differed, increased bacterial but decreased fungal diversity and effects of woody encroachment within the encroached watershed were minimal. High-severity burns in the fire-protected watershed led to a novel soil system state distinct from non-encroached and encroached soil systems. We conclude that severe fires may open grassland restoration opportunities to manipulate soil chemistry and microbial communities in shrub-encroached habitats.

Pyrolyzed Substrates Induce Aromatic Compound Metabolism in the Post-fire Fungus, Pyronema domesticum

Wildfires represent a fundamental and profound disturbance in many ecosystems, and their frequency and severity are increasing in many regions of the world. Fire affects soil by removing carbon in the form of CO2 and transforming remaining surface carbon into pyrolyzed organic matter (PyOM). Fires also generate substantial necromass at depths where the heat kills soil organisms but does not catalyze the formation of PyOM. Pyronema species strongly dominate soil fungal communities within weeks to months after fire. However, the carbon pool (i.e., necromass or PyOM) that fuels their rise in abundance is unknown. We used a Pyronema domesticum isolate from the catastrophic 2013 Rim Fire (CA, United States) to ask whether P. domesticum is capable of metabolizing PyOM. Pyronema domesticum grew readily on agar media where the sole carbon source was PyOM (specifically, pine wood PyOM produced at 750°C). Using RNAseq, we investigated the response of P. domesticum to PyOM and observed a comprehensive induction of genes involved in the metabolism and mineralization of aromatic compounds, typical of those found in PyOM. Lastly, we used 13C-labeled 750°C PyOM to demonstrate that P. domesticum is capable of mineralizing PyOM to CO2. Collectively, our results indicate a robust potential for P. domesticum to liberate carbon from PyOM in post-fire ecosystems and return it to the bioavailable carbon pool.