Soil Assemblages Research Articles

Microarthropod responses to fire: vegetation cover modulates impacts on Collembola and Acari assemblages in Mediterranean area

BackgroundIn the Mediterranean region, fire is a recurring disturbance that impacts both surface and underground organisms. While the effects on plants and surface animals are well-studied, the consequences for soil microarthropods are often overlooked. This research addresses the microarthropod responses to fire by comparing post-fire Collembola and Acari assemblages in soils with different vegetation covers. Three years post-fire, surface soils were sampled within the Vesuvius National Park (Southern Italy) from a total of 24 sites, comprising 6 sites each under holm oak (HO), pine (P), black locust (BL), and herbaceous (H) vegetation. Within each vegetation cover, sites were further categorized into three unburnt (NB) and three burnt (B) sites for comprehensive analysis. Collembola and Acari were extracted, identified at the family and suborder level, respectively and analyzed for density and taxa richness.ResultsThe results highlighted that fire alone did not impact microarthropod communities, but its effects varied according to the vegetation covers. Microarthropod abundance declined in burnt soils under P, and increased in burnt soils under BL. Furthermore, eu-edaphic organisms (Onychiuridae, Oribatida), typical of stable environments, decreased in soils under P, and increased in soils under black locust.ConclusionsFire impact on microarthropod communities changed according to the vegetation covers, highlighting the importance of considering vegetation type when managing post-fire landscapes. The rapid recovery of microarthropod communities under some vegetation covers suggests that fire may not universally impair soil biodiversity in Mediterranean environments.

Assessing phytolith preservation in a Late Quaternary loess-paleosol sequence from the Kashmir Valley, Northwest Himalaya, India

Phytolith content and its preservation in soils form a robust tool for paleoecological reconstruction. Post-depositional processes, however, influence the preservation of phytolith assemblages in soils thus making the paleoecological inferences biased. Here we evaluated the preservation of phytoliths in a Late Quaternary loess-paleosol sequence (LPS) from Kashmir Valley, northwest Himalaya. The soil micromorphological study, physicochemical parameters, phytolith morphometry, and phytolith translocation rates were employed to assess phytolith preservation and absence (not recorded) in the various litho-units of the Wanihama LPS. The comparison of phytolith content and soil physio-chemical parameters including pH, electrical conductivity, available N, P, K, organic carbon, extractable Fe, Zn, Mn and Cu do not show any significant correlation. This suggests that soil physicochemical parameters have a minor role in regulating the preservation of phytoliths in the LPS. The depth distribution of phytoliths exhibits an inconsistent pattern and phytolith content doesn't decrease systematically with depth. The phytolith content usually follows the loess-paleosol stratigraphy, with low concentrations in loess units and high concentrations in paleosols indicating that phytolith assemblages in the LPS have not been altered or translocated as a result of pedogenic processes. The micromorphological observations suggest weak pedogenesis and the sequence does not seem to be significantly mixed by bioturbation activities. This is augmented by the low translocation rate of <18%, and phytolith morphometry suggesting well-preserved phytoliths with minimum morphological alterations along the depth. The absence of phytoliths at certain stratigraphic units in the LPS thus suggests that climatic conditions rather than physicochemical parameters determine the phytolith preservation and their content in the Kashmir LPS.

A comparison of phytolith assemblages in surface soils along the 400-mm and 600-mm mean annual precipitation isohyets in Northeast China

A comparison of phytolith assemblages in surface soils along the 400-mm and 600-mm mean annual precipitation isohyets in Northeast China

Composition of soil Frankia assemblages across ecological drivers parallels that of nodule assemblages in Alnus incana ssp. tenuifolia in interior Alaska.

In root nodule symbioses (RNS) between nitrogen (N)-fixing bacteria and plants, bacterial symbionts cycle between nodule-inhabiting and soil-inhabiting niches that exert differential selection pressures on bacterial traits. Little is known about how the resulting evolutionary tension between host plants and symbiotic bacteria structures naturally occurring bacterial assemblages in soils. We used DNA cloning to examine soil-dwelling assemblages of the actinorhizal symbiont Frankia in sites with long-term stable assemblages in Alnus incana ssp. tenuifolia nodules. We compared: (1) phylogenetic diversity of Frankia in soil versus nodules, (2) change in Frankia assemblages in soil versus nodules in response to environmental variation: both across succession, and in response to long-term fertilization with N and phosphorus, and (3) soil assemblages in the presence and absence of host plants. Phylogenetic diversity was much greater in soil-dwelling than nodule-dwelling assemblages and fell into two large clades not previously observed. The presence of host plants was associated with enhanced representation of genotypes specific to A. tenuifolia, and decreased representation of genotypes specific to a second Alnus species. The relative proportion of symbiotic sequence groups across a primary chronosequence was similar in both soil and nodule assemblages. Contrary to expectations, both N and P enhanced symbiotic genotypes relative to non-symbiotic ones. Our results provide a rare set of field observations against which predictions from theoretical and experimental work in the evolutionary ecology of RNS can be compared.

Effects of land use and soil properties on taxon richness and abundance of soil assemblages

AbstractLand‐use change and habitat degradation are among the biggest drivers of aboveground biodiversity worldwide but their effects on soil biodiversity are less well known, despite the importance of soil organisms in developing soil structure, nutrient cycling and water drainage. Combining a global compilation of biodiversity data from soil assemblages collated as part of the PREDICTS project with global data on soil characteristics, we modelled how taxon richness and total abundance of soil organisms have responded to land use. We also estimated the global Biodiversity Intactness Index (BII)—the average abundance and compositional similarity of taxa that remain in an area, compared to a minimally impacted baseline, for soil biodiversity. This is the first time the BII has been calculated for soil biodiversity. Relative to undisturbed vegetation, soil organism total abundance and taxon richness were reduced in all land uses except pasture. Soil properties mediated the response of soil biota, but not in a consistent way across land uses. The global soil BII in cropland is, on average, a third of that originally present. However, in grazed sites the decline is less severe. The BII of secondary vegetation depends on age, with sites with younger growth showing a lower BII than mature vegetation. We conclude that land‐use change has reduced local soil biodiversity worldwide, and this further supports the proposition that soil biota should be considered explicitly when using global models to estimate the state of biodiversity.

Complexity of clay minerals and its effects on silicon dynamics in hypersaline coastal wetland soils, Brazil

Context Tidal dynamics and high evaporative rates in hypersaline tidal flat (HTF) soils favour a range of clay reactions and the formation of complex clay assemblages. HTFs have a geochemical environment conducive to mineral reactions, and therefore, clay mineral alteration controls essential nutrients in coastal wetlands. Aims The crystallochemical characteristics of clay minerals from two HTFs were studied to provide insights into the complexity of fine clay assemblages in HTF soils and their effects on Si biogeochemistry. Methods The fine clay fraction (&lt;0.2 μm) from these HTFs were investigated using X-ray diffraction (XRD) modelling, XRF, FTIR, TEM–EDS, and silicon sequential extractions. Key results The results have indicated the presence of endmembers and R0 mixed-layered minerals such as kaolinite, smectite, illite, kaolinite–smectite (K–S), kaolinite–illite (K–I), illite–smectite (I–S), and illite–vermiculite (I–V). In general, K–S was the dominant mineral in the samples, occurring in a range of kaolinite layers. Alteration of detrital kaolinite to other mixed-layered minerals occurs in soils, leading to silicon removal from the soil solution because of mineral genesis. There is Mg enrichment at the expense of Al in the samples, and bio-opal appears to be the source of Si for the kaolinite alteration process. Conclusions Our findings indicate that clay authigenesis is an important factor controlling Si dynamics in HTF soils, acting as a sink of Si during the formation of new clay phases. Implications Chemical reactions involving clay minerals are critical for deepening our understanding of the biogeochemistry of wetland soils.

Distribution of Soil Microbes in Urban Parks: An Effect of Under-Tree Crown and Hillside Position on Testate Amoeba Assemblages in Subtropics (Shenzhen, China)

Testate amoebae (TA) are important components of soil ecosystems, where they play an essential role in belowground food webs. In this study, we examined species composition, diversity, and structure of TA assemblages in soils beneath tree crowns (microscale) at three slope positions (mesoscale) in subtropical urban parks in Shenzhen, China. Forty-two species of TA belonging to 18 genera were identified in 81 samples. TA assemblages were the most diverse and abundant in the center of the tree crown comparing with other under-tree habitats. Foot of the hills harbored higher TA abundance and diversity comparing with upper locations along the hillslopes. The distribution of TA was mostly driven by under-crown and hillside positions but not by elementary environmental conditions such as pH, moisture content and thickness of leaf litter layer. None of later factors were sufficient in shaping TA assemblage composition. The findings of our study suggest that in regional studies of soil microbial eukaryotes both micro- (i.e., under-crown) and mesoscale (i.e., the slope position) heterogeneity should be considered.

Land use and soil characteristics affect soil organisms differently from above-ground assemblages

BackgroundLand-use is a major driver of changes in biodiversity worldwide, but studies have overwhelmingly focused on above-ground taxa: the effects on soil biodiversity are less well known, despite the importance of soil organisms in ecosystem functioning. We modelled data from a global biodiversity database to compare how the abundance of soil-dwelling and above-ground organisms responded to land use and soil properties.ResultsWe found that land use affects overall abundance differently in soil and above-ground assemblages. The abundance of soil organisms was markedly lower in cropland and plantation habitats than in primary vegetation and pasture. Soil properties influenced the abundance of soil biota in ways that differed among land uses, suggesting they shape both abundance and its response to land use.ConclusionsOur results caution against assuming models or indicators derived from above-ground data can apply to soil assemblages and highlight the potential value of incorporating soil properties into biodiversity models.

Linking bacterial and fungal assemblages to soil nutrient cycling within different aggregate sizes in agroecosystem.

Soil aggregates provide spatially heterogeneous microhabitats that support the coexistence of soil microbes. However, there remains a lack of detailed assessment of the mechanism underlying aggregate-microbiome formation and impact on soil function. Here, the microbial assemblages within four different aggregate sizes and their correlation with microbial activities related to nutrient cycling were studied in rice fields in Southern China. The results show that deterministic and stochastic processes govern bacterial and fungal assemblages in agricultural soil, respectively. The contribution of determinism to bacterial assemblage improved as aggregate size decreased. In contrast, the importance of stochasticity to fungal assemblage was higher in macroaggregates (>0.25 mm in diameter) than in microaggregates (<0.25 mm). The association between microbial assemblages and nutrient cycling was aggregate-specific. Compared with microaggregates, the impacts of bacterial and fungal assemblages on carbon, nitrogen, and phosphorus cycling within macroaggregates were more easily regulated by soil properties (i.e., soil organic carbon and total phosphorus). Additionally, soil nutrient cycling was positively correlated with deterministic bacterial assemblage but negatively correlated with stochastic fungal assemblage in microaggregates, implying that bacterial community may accelerate soil functions when deterministic selection increases. Overall, our study illustrates the ecological mechanisms underlying the association between microbial assemblages and soil functions in aggregates and highlights that the assembly of aggregate microbes should be explicitly considered for revealing the ecological interactions between agricultural soil and microbial communities.

Detection of iron-bearing mineral assemblages in Nainarmalai granulite region, south India, based on satellite image processing and geochemical anomalies.

Although India's large iron ore reserves are well known, there are still few studies and research on iron ore prospecting in smaller deposits or the deposits with lower grade. Remote sensing concepts are useful to target for mineral exploration, since it covers a large area at low cost. In this research spectral remote sensing and digital image processing of ASTER data to locate and delineate the regions with iron oxide-bearing soils in granulite terrain at Nainnarmalai (southern India) that has hypothetical reserve 8.2 million tons of iron in sub-surface banded magnetite quartzites. The image-based study component involved pre-processing atmospheric correction and processing of the image data reminiscent of band ratio and band mixture to locate iron-bearing soils. We used blending of bands 5/3 + 1/2 to delineate ferrous iron oxide, band combination of 2/1 to delineate ferric iron oxide, and band ratio of 5/4 to delineate the lateritic soil. Further, the linear spectral unmixing outcome of ASRER data was evaluated concerning the ground truth of geochemical compositions of samples from the study area. Our results showed that image processing of the ASTER satellite data has the potential to delineate ferric, ferrous, and lateritic mineral assemblages in the iron-bearing soils with minimal requirement of ground truth verification. This research work aided in increasing trust in the use of space-based data for mineral prospecting. Image processing has demonstrated that ASTER data can be used to enhance iron ore exploration and the discovery of new mineralized areas.

The fictional soils of a ‘sustainable’ Anthropocene: A new materialist story of the soils of the Queen Elizabeth Olympic Park

The Queen Elizabeth Olympic Park in London has been celebrated as an exemplar of sustainable landscape architecture and regeneration. Yet tracing the new materialist histories of its enmeshed soils reveals how complex sustainable landscape architecture is. On the one hand, the park has expertly recycled and locally sourced its materials. On the other, the socio-ecosystems of its soil assemblages have been pulverized, treated and mixed to create a new profile of synthetic geological strata. Their history and life have been erased. The subterranean sections through this park are caricatures of a ‘sustainable Anthropocene’. Here, the anthropogenic geology supporting the vision of idealized future ecosystems is used for the global marketing of a nation and property developments. This project indicates a destructive systemic blindness in sustainable approaches and the need for truly regenerative design processes, based on working with a place, including the various (other-than) human inhabitants, instead of solely mining its materials to create a perfect vision anew.

The Right Place at the Right Time: Seasonal Variation of Bacterial Communities in Arid Avicennia marina Soils in the Red Sea Is Specific to Its Position in the Intertidal

Mangrove forests play an important role in facilitating biogeochemical pathways and cycling acting as blue carbon sinks. These services are primarily regulated by the activity of the soil microbiome. However, there is still limited research into spatial and temporal variation patterns of bacterial community assemblages in mangrove soils. This study investigated important ecological scales of microprocesses that govern microbial communities in an arid mangrove ecosystem. Shifts in microbial community composition were influenced by fluctuations in environmental factors within the mangrove forests of the Red Sea influenced by seasonal changes in sea level. Notably, in summer microbial communities in shrub sites differed significantly from the fringe and the winter samples, with lower alpha diversity yet a higher dominance of specialized species capable of surviving in extreme conditions. The onset of dispersal limitation and heterogenous selection and the reduction of drift are likely the main forces shaping community assemblages. Specifically, in summer lower mean tidal levels eliminate tidal inundation creating a harsh high salinity and high temperature environment with no tidal connection thereby influencing the onset of dispersal limitation. An increased understanding of the spatial and temporal variation of bacterial communities is critical when assessing delivery of ecosystem services and their role in soil biogeochemical processes.

Phylogenies of traits and functions in soil invertebrate assemblages

AbstractSoil invertebrates are members of terrestrial ecosystems, contributing to the processing of organic matter, resulting in carbon and nutrient cycling that is essential for continuous productivity. By linking species delineations, morphological traits and measured or inferred functional roles, we demonstrate a method for functional identification of soil faunal assemblages based on molecular information. Here we align the genetic inter‐relatedness and functional trait expression in nematodes and springtails. Nematodes were assigned feeding guild, plant parasitic feeding type and coloniser‐persister (c‐p) value, with springtail sequences assigned to soil vertical stratification level, soil moisture preference and a selection of morphological traits.We found that both nematode and springtail feeding preferences show significant phylogenetic clustering. In contrast, greater dispersal was found amongst nematode coloniser‐persister (c‐p) values and springtail soil vertical stratification level and moisture preferences. Minimum patristic (p) distances between species supported the clustering amongst nematode feeding guilds, with plant feeders being separated from all other guilds by at least p = 0.99. Distances between endoparasitic, ectoparasitic and sedentary plant parasitic nematodes were also distinct with minimal distances of p = 0.35–0.72 between parasitic types. Springtail stratification level and soil moisture preferences showed greater dispersion across phylogenies, with negligible between‐group minimum patristic distances. However, nematode c‐p values and springtail moisture preference alignments indicate some genetic conservation at the genus level.These results indicate how ecosystems can direct trait conservation beyond that of environmental stimuli. Being able to assign functional traits to novel sequences will allow individual species' likely contribution to ecosystem functioning to be inferred without the need for exact taxonomic identification. More broadly, such information can advance our understanding of the evolution of soil faunal traits and the contribution of diverse soil assemblages to functional soil systems, particularly those with a high proportion of undescribed species.

Biogels in Soils: Plant Mucilage as a Biofilm Matrix That Shapes the Rhizosphere Microbial Habitat.

Mucilage is a gelatinous high-molecular-weight substance produced by almost all plants, serving numerous functions for plant and soil. To date, research has mainly focused on hydraulic and physical functions of mucilage in the rhizosphere. Studies on the relevance of mucilage as a microbial habitat are scarce. Extracellular polymeric substances (EPS) are similarly gelatinous high-molecular-weight substances produced by microorganisms. EPS support the establishment of microbial assemblages in soils, mainly through providing a moist environment, a protective barrier, and serving as carbon and nutrient sources. We propose that mucilage shares physical and chemical properties with EPS, functioning similarly as a biofilm matrix covering a large extent of the rhizosphere. Our analyses found no evidence of consistent differences in viscosity and surface tension between EPS and mucilage, these being important physical properties. With regard to chemical composition, polysaccharide, protein, neutral monosaccharide, and uronic acid composition also showed no consistent differences between these biogels. Our analyses and literature review suggest that all major functions known for EPS and required for biofilm formation are also provided by mucilage, offering a protected habitat optimized for nutrient mobilization. Mucilage enables high rhizo-microbial abundance and activity by functioning as carbon and nutrient source. We suggest that the role of mucilage as a biofilm matrix has been underestimated, and should be considered in conceptual models of the rhizosphere.

Contrasting Effects of Local Environmental and Biogeographic Factors on the Composition and Structure of Bacterial Communities in Arid Monospecific Mangrove Soils.

ABSTRACTMangrove forests are important biotic sinks of atmospheric CO2 and play an integral role in nutrient-cycling and decontamination of coastal waters, thereby mitigating climatic and anthropogenic stressors. These services are primarily regulated by the activity of the soil microbiome. To understand how environmental changes may affect this vital part of the ecosystem, it is key to understand the patterns that drive microbial community assembly in mangrove forest soils. High-throughput amplicon sequencing (16S rRNA) was applied on samples from arid Avicennia marina forests across different spatial scales from local to regional. Alongside conventional analyses of community ecology, microbial co-occurrence networks were assessed to investigate differences in composition and structure of the bacterial community. The bacterial community composition varied more strongly along an intertidal gradient within each mangrove forest, than between forests in different geographic regions (Australia/Saudi Arabia). In contrast, co-occurrence networks differed primarily between geographic regions, illustrating that the structure of the bacterial community is not necessarily linked to its composition. The local diversity in mangrove forest soils may have important implications for the quantification of biogeochemical processes and is important to consider when planning restoration activities.IMPORTANCE Mangrove ecosystems are increasingly being recognized for their potential to sequester atmospheric carbon, thereby mitigating the effects of anthropogenically driven greenhouse gas emissions. The bacterial community in the soils plays an important role in the breakdown and recycling of carbon and other nutrients. To assess and predict changes in carbon storage, it is important to understand how the bacterial community is shaped by its environment. Here, we compared the bacterial communities of mangrove forests on different spatial scales, from local within-forest to biogeographic comparisons. The bacterial community composition differed more between distinct intertidal zones of the same forest than between forests in distant geographic regions. The calculated network structure of theoretically interacting bacteria, however, differed most between the geographic regions. Our findings highlight the importance of local environmental factors in shaping the microbial soil community in mangroves and highlight a disconnect between community composition and structure in microbial soil assemblages.

Cropping system exerts stronger influence on antibiotic resistance gene assemblages in greenhouse soils than reclaimed wastewater irrigation

The effects of reclaimed wastewater (RW) irrigation on the spread of antibiotic resistance genes (ARGs) in soil is modulated by a myriad of biotic and abiotic factors and their relative significance remains vague. We compared microbial communities, assemblages of genes associated with microbial resistance to antibiotics, biocides and metals, and insertion sequences (ISs) in soils following 16 years of irrigation with groundwater (GW), RW or alternately with GW and RW in two greenhouses with different cropping systems, using shotgun metagenome sequencing. The results showed that cropping system exerted greater influence than irrigation on the profile of ISs and resistance genes. This influence was most strongly associated with concentrations of copper, mercury and perfloxacin in the soils. There was no significant difference in soil ARG profiles between continuous RW irrigation and alternating GW and RW irrigation. Proteobacteria, Actinobacteria and Firmicutes and a limited number of ISs were closely associated with the detected ARGs. Most ARGs were found to co-occur with metal and biocide resistance genes through the mechanism of efflux pumps. These findings highlight the significance of understanding and improving crop management in mitigating the dissemination of ARGs in soils irrigated with RW.

Are modern pollen assemblages from soils and mosses the same? A comparison of natural pollen traps from subtropical China

This study investigated the pollen spectra from 46 pairs of soil and moss samples (pairs collected within a 1 m2 squared area). The samples were collected from six common subtropical vegetation communities in the Meiling Mountains, southeast China, with the vegetation proportions recorded at the collection point. Principal Component Analysis (PCA) was used to investigate the separation of the paired assemblages and to determine whether different plant communities produced distinctive pollen spectra. Paired soil and moss samples captured similar levels of variability in the pollen assemblages retained, but there are systematic differences in the mean values of key groups of taxa. Monte Carlo sampling shows that, in most cases, intra-pair differences are greater than could be explained by counting uncertainty alone.In this study, discriminant analysis of surface soil and moss found that 91.3% of the soil samples and 87% of the moss samples were correctly classified into their vegetation communities. However, the detailed pollen assemblages suggest that mosses provide a more accurate representation of the contemporary vegetation composition than soils.Pollen assemblages from moss samples seem to record local vegetation more accurately than those from soil samples. Higher vegetation diversity within an arboreal forest community leads to greater differences between moss-soil pairs. In bamboo forests, pollen assemblages in soils and moss show strong influence from the surrounding communities, which makes it hard to identify bamboo forest via surface sample pollen assemblages alone.

Elevational distribution and occurrence of arbuscular mycorrhizal fungi in non-host Carex capillacea.

Little is known about Arbuscular mycorrhizal (AM) fungal colonization and community composition in non-mycorrhizal (NM) plants, especially along elevational gradients. This study explores this question using a NM plant, Carex capillacea, at Mount Segrila, Tibet. Here, C. capillacea, its rhizosphere soil, and the neighboring mycotrophic plant Poa annua were sampled at four elevations to evaluate and compare their AM fungi colonization and communities. The results showed that AM fungal colonization density of C. capillacea was negatively correlated with elevation and biomass of total NM plants per quadrat. AM fungal diversity and community composition between C. capillacea and P. annua showed a similar pattern. In addition, elevation and soil did not significantly influence the AM community in C. capillacea, while they were important abiotic factors for assemblages in rhizosphere soil and P. annua. These findings support that a broad array of AM fungi colonize the root of C. capillacea, and a mycelial network from a co-occurring host plant might shape the AM fungal communities in C. capillacea along the elevation gradient. The co-occurrence patterns of AM fungi associated with non-mycotrophic species and adjacent mycotrophic species have important implications for understanding AM fungal distribution patterns and plant-AM interactions.

Sugar and organic acid availability modulate soil diazotroph community assembly and species co-occurrence patterns on the Tibetan Plateau.

Metabolites can mediate species interactions and the assembly of microbial communities. However, how these chemicals relate to the assembly processes and co-occurrence patterns of diazotrophic assemblages in root-associated soils remains largely unknown. Here, we examined the diversity and assembly of diazotrophic communities and further deciphered their links with metabolites on Tibetan Plateau. We found that the distribution of sugars and organic acids in the root-associated soils was significantly correlated with the richness of diazotrophs. The presence of these two soil metabolites explains the variability in diazotrophic community compositions. The differential concentrations of these metabolites were significantly linked with the distinctive abundances of diazotrophic taxa in same land types dominated by different plants or dissimilar soils by same plants. The assembly of diazotrophic communities is subject to deterministic ecological processes, which are widely modulated by the variety and amount of sugars and organic acids. Organic acids, for instance, 3-(4-hydroxyphenyl)propionic acid and citric acid, were effective predictors of the characteristics of diazotrophic assemblages across desert habitats. Diazotrophic co-occurrence networks tended to be more complex and connected within different land types covered by the same plant species. The concentrations of multiple sugars and organic acids were coupled significantly with the distribution of keystone species, such as Azotobacter, Azospirillum, Bradyrhizobium, and Mesorhizobium, in the co-occurrence network. These findings provide new insights into the assembly mechanisms of root-associated diazotrophic communities across the desert ecosystems of the Tibetan Plateau.Key points• Soil metabolites were significantly linked to the diversity of diazotrophic community.• Soil metabolites determined the assembly of diazotrophic community.• Sugars and organic acids were coupled mainly with keystone species in networks.

Soil Layers Matter: Vertical Stratification of Root-Associated Fungal Assemblages in Temperate Forests Reveals Differences in Habitat Colonization.

Ectomycorrhizal and saprotrophic fungi play pivotal roles in ecosystem functioning. Here, we studied the vertical differentiation of root-associated fungi (RAF) in temperate forests. We analysed RAF assemblages in the organic and mineral soil from 150 experimental forest plots across three biogeographic regions spanning a distance of about 800 km. Saprotrophic RAF showed the highest richness in organic and symbiotrophic RAF in mineral soil. Symbiotrophic RAF exhibited higher relative abundances than saprotrophic fungi in both soil layers. Beta-diversity of RAF was mainly due to turnover between organic and mineral soil and showed regional differences for symbiotrophic and saprotrophic fungi. Regional differences were also found for different phylogenetic levels, i.e., fungal orders and indicator species in the organic and mineral soil, supporting that habitat conditions strongly influence differentiation of RAF assemblages. Important exceptions were fungal orders that occurred irrespective of the habitat conditions in distinct soil layers across the biogeographic gradient: Russulales and Cantharellales (ectomycorrhizal fungi) were enriched in RAF assemblages in mineral soil, whereas saprotrophic Polyporales and Sordariales and ectomycorrhizal Boletales were enriched in RAF assemblages in the organic layer. These results underpin a phylogenetic signature for niche partitioning at the rank of fungal orders and suggest that RAF assembly entails two strategies encompassing flexible and territorial habitat colonization by different fungal taxa.