Groups Of Soil Organisms Research Articles

Decoupled responses of plants and soil biota to global change across the world’s land ecosystems

Understanding the concurrent responses of aboveground and belowground biota compartments to global changes is crucial for the maintenance of ecosystem functions and biodiversity conservation. We conduct a comprehensive analysis synthesizing data from 13,209 single observations and 3223 pairwise observations from 1166 publications across the world terrestrial ecosystems to examine the responses of plants and soil organisms and their synchronization. We find that global change factors (GCFs) generally promote plant biomass but decreased plant species diversity. In comparison, the responses of belowground soil biota to GCFs are more variable and harder to predict. The analysis of the paired aboveground and belowground observations demonstrate that responses of plants and soil organisms to GCFs are decoupled among diverse groups of soil organisms for different biomes. Our study highlights the importance of integrative research on the aboveground-belowground system for improving predictions regarding the consequences of global environmental change.

Typical earthworm assemblages of European ecosystem types

AbstractFor nature conservation and planning, terrestrial ecosystems are commonly classified based on their plant communities. Although soils are fundamental to ecosystem functioning, ecosystem classifications based on soil organisms are rare, and it is poorly understood whether their assemblage compositions follow existing classification schemes. We examined whether commonly used ecosystem types capture variation in earthworm (Lumbricidae) assemblages—a crucial biotic component of soil ecosystems. To this end, we created four ecosystem classifications by combining large‐scale climatic classifications (Biogeographic Regions [BGR] and Holdridge Life Zones [HLZ]) with small‐scale land cover classifications (CORINE Land Cover [CLC] and European Nature Information System [EUNIS]). European earthworm assemblage data from the sWORM and Edaphobase databases were analysed for variation in composition within and among ecosystem types, using Permutational Analysis of Variance and Analysis of Similarities. Additionally, we used Typical Species Analysis to establish typical earthworm assemblages (TAs) for each ecosystem type. Ecosystem classifications using the BGR explained more variance than HLZ, but HLZ showed a higher separation of assemblages between ecosystem types. The differentiation between Atlantic and Continental climates in the BGR could explain the superiority over the HLZ, which had only one category for the cool temperate zone of our study region. The typical assemblages contained on average six species, with some habitat generalists present in most. This study shows that combinations of ecosystem properties from different spatial scales can be used to distinguish between earthworm assemblages at the European level. However, earthworm assemblages across Europe were highly similar due to low species richness and the dominance of a few widespread species. This limits the possibility of applying TAs on large spatial scales, for example, for environmental monitoring. We suggest that future studies should explore the use of more species‐rich groups of soil organisms to characterize ecosystem types.

Limited dependence on soil nitrogen fixation as subtropical forests develop

Soil nitrogen (N) fixation, driven by microbial reactions, is critical to support the entrance of nitrogen in nutrient poor and pioneer ecosystems. However, how and why N fixation and soil diazotrophs evolve as forests develop remain poorly understood. Here, we used a 60-year forest rewilding chronosequence and found that soil N fixation activity gradually decreased with increasing forest age, experiencing dramatic drops of 64.8% in intermediate stages and 93.0% in the oldest forests. Further analyses revealed loses in diazotrophic diversity and a significant reduction in the abundance of important diazotrophs (e.g., Desulfovibrio and Pseudomonas) as forest develops. This reduction in N fixation, and associated shifts in soil microbes, was driven by acidification and increases in N content during forest succession. Our results provide new insights on the life history of one of the most important groups of soil organisms in terrestrial ecosystems, with consequences for understanding the buildup of nutrients as forest soil develops.

Interspecific interactions between crops influence soil functional groups and networks in a maize/soybean intercropping system

Despite increasing evidence that intercropping systems may increase crop productivity, little is known about whether and how soil biota change under interspecific competition among plants. A field experiment with maize/soybean intercropping and the corresponding monoculture systems was conducted under four nitrogen fertilization regimes to investigate the effects of interspecific plant interactions on grain yield, soil properties (β-glucosidase and water-soluble carbohydrates), and biotic communities (bacteria, fungi, and nematodes). The soils under maize and soybean in the intercropping system were sampled separately to represent intercropped maize and intercropped soybean, respectively. Compared to monocultures, the complexity and robustness of soil networks comprising bacterial, fungal, and nematode communities increased in intercropped maize soils, but densities of plant parasitic nematodes and β-glucosidase activity were reduced. Intercropped soybean soils had lower C availability due to chronic shading by maize, but a significant increase was found in saprophytic fungi, and plant parasitic nematodes compared to soybean monoculture soils. Although intercropped soybean suffered from interspecific competition with maize, the interactions within the fungal community increased for both crop species in the intercropping system. Our study demonstrates that increased carbon uptake in maize due to increased light capture in the intercropping system can facilitate nutrient cycling by altering the abundance of functional groups of soil organisms, such as saprophytic fungi, and enhancing network complexity and stability. We detected a trade-off between productivity and soil nematode diversity in the intercropping system under nitrogen fertilization, the yield of maize increased but soil nematode richness decreased at low nitrogen level, while the yield of soybean decreased but the nematode richness increased at high nitrogen level. These findings show that both trade-offs and benefits occur in intercropping systems and highlight the role of plant-soil biota interactions in such systems.

An alternative risk assessment framework for tropical soil multi-metal contamination using arbuscular mycorrhizal fungi

Arbuscular mycorrhizal fungi (AMF) are a key group of soil organisms involved in several ecosystem services, but they had not been explored in retrospective ecological risk assessment (ERA) schemes, partially due to a lack of experimental protocols. We aimed to perform a site-specific test to assess the effects of multiple metal contaminated soil (Zn, Cu, Cd, and Pb) on several ecotypes of AMF and evaluate the conceptual fitness of the performed AMF test to include in the TRIAD approach of ERA schemes. The results demonstrated that increasing metal contaminated soil proportions that inhibited 50 % (IC50) of spore germination varied from 28 to >80. Ecotypes such as Claroideoglomus etunicatum (IC50 > 80) and Racocetra gregaria (IC50 > 80) experienced 50 % reduction in spore germination at metals concentrations of 10,776.3 for Zn, 1015.2 Cu, 65.5 Cd, 140.2 mg dm−3 Pb, that are 3 times higher than those for Acaulospora mellea CMM101 (IC50 28 [16.2–39.8]) (3441.7 Zn, 333.9 Cu, 17.8 Cd, 56.5 mg dm−3 Pb). In the evaluation of the suitability of the AMF ecotoxicological test to ERA, both spore germination and germinative tube growth were best evaluated and thus suitable in the following descending order: Tier III, Tier II, and Tier I. Variable effects of multiple-metal contamination on the ecotypes indicates how AMF community is affected in its pre-symbiotic structures. The ecotoxicological test allowed the selection of two species with the greatest sensitivity (Ambispora appendicula and Rhizophagus clarus CMM103) to the metal matrix, with the potential to best fit ERA objectives. The site-specific ecotoxicological test with AMF ex-situ proved adequate as an alternative test for Tiers II and III of TRIAD ERA schemes for metal contaminated areas. Data generated through test results, such as the inhibition concentrations (ICs), could be incorporated into ERAs risk indexes, increasing its ecological relevance, and reducing overall uncertainties.

Fertilization alters the abundance but not the diversity of soil fauna: A meta‐analysis

AbstractAimSoil fauna, a functionally important group of soil organisms, are greatly affected by fertilization. However, it is still debated whether and how fertilization affects the soil faunal community. Here, we aimed to synthesize the global patterns of soil fauna communities in response to fertilization in terrestrial ecosystems.LocationGlobal.Time period1997–2021.Major taxa studiedSoil fauna.MethodsWe examined the effects of fertilization on the abundance, number of groups and Shannon diversity of soil fauna by synthesizing 1218 observations based on 39 published studies. We also explored the associations between fertilization‐induced changes in the soil faunal community and changes in soil and microbial properties.ResultsFertilization increased the abundance of soil fauna by 56.3%, without significantly affecting the number of groups and the Shannon index. The type of fertilizer affected the responses of soil faunal abundance, and the effects of fertilizer type were altered by climate zones, ecosystem types and soil depths. Both organic and organic–mineral fertilizer treatments significantly increased the abundance of soil fauna in most climate zones, ecosystem types and soil depths, whereas mineral fertilizer treatment had no such effect. Additionally, we found inconsistent responses of soil fauna to fertilization among different taxonomic groups, not only at the order level but also at the class level, providing evidence for the idiosyncratic nature of the effects of fertilization on soil fauna. Furthermore, our regression analysis showed that changes in food resources, including soil nutrients and microbes, were crucial controls for the response of soil faunal abundance to fertilization.Main conclusionsFertilization generally increased soil faunal abundance at the global scale by affecting food resources, and the effects of fertilization were dependent on the specific soil fauna and type of fertilizer. We suggest the use of organic or organic–mineral fertilizers, rather than mineral fertilizers, to increase the benefits on specific soil fauna.

Spatial assortment of soil organisms supports the size-plasticity hypothesis

The size-plasticity hypothesis posits that larger size organisms are less plastic in their metabolic rates and, therefore, are more strongly environmental-filtered than smaller organisms. Many studies have supported this hypothesis by evaluating the relative roles of environmental filtration and dispersal for different taxonomic groups of soil organisms. Most observations are made at large spatial scales, which are assumed to have a wide array of varying habitats. However, since urbanization causes habitat fragmentation at smaller regional scales, testing the size-plasticity hypothesis at this scale would help better understand the spatial assortment of urban soil organisms which, in turn, would help to develop improved management and conservation strategies for urban soil health. Here, we used DNA metabarcoding on five groups of soil biota (bacteria, fungi, protists, nematodes, and invertebrates) to assess the relative importance of dispersal and environmental filters to examine the size-plasticity hypothesis at this spatial scale in an urban environment. We observed strong distance-decay of community similarities associated with higher levels of stochastic changes in bacteria, nematode, and protist communities but not fungal or invertebrate communities. Bacterial communities occupied the widest niche followed by protists and nematodes, potentially because of their higher dispersal abilities compared to the larger soil organisms. Null deviation of communities varied with taxonomic groups where bacteria and nematodes were mainly driven by homogenizing dispersal, protists and fungi by drift, and soil invertebrates by environmental selection. We further identified a small percentage of locally-adapted taxa (2.1%) that could be focal taxa for conservation and restoration efforts by, for example, restoring their habitats and enhancing their regional connectivity. These results support the size-plasticity hypothesis at the relatively unexplored regional scale in an urbanization context, and provide new information for improving urban soil health and sustainable city models.

Modelling litter decomposition rates along a geographic, climatic, and land-use gradient in Southern Amazonia and Pará

The study aimed to investigate the effect on litter decomposition of the geographical and land-use gradient from the dry Cerrado in Mato Grosso to the southern Amazonian rainforest in Pará, Brazil. The study area also represents a gradient of land-use intensification, reaching from the southern Cerrado region which had the most active land use change and agricultural intensification in the past to the northern rainforest region where agricultural use is currently intensifying. We assessed the effects on litter decomposition of climate (seasonality: rainy vs dry), litter quality (litter type: standard maize litter vs local habitat litter), disturbance (land-use: forest vs pasture vs cropland), soil organisms (soil fauna: inclusion vs exclusion), and original land cover/vegetation gradient (region: savanna vs transitional zone vs rain forest). Our results showed that the contribution of the different soil organism groups (mesh size) to litter decomposition was strongly influenced by the change in land-use, but also by the original land-cover/vegetation of the region. The overall effect of climate seasonality on decomposition was particularly pronounced at higher latitudes, whereas at lower latitudes only minimal effects were found.

Soil-dwelling species-based biomarker as a sensitivity-risk measure of terrestrial ecosystems response to microplastics: A dose–response modeling approach

Microplastics (MPs) dispersed throughout terrestrial ecosystems is a growing global concern, yet their potential risks on terrestrial ecosystems are poorly understood from a mechanistic viewpoint. A novel empirical approach to assess relative sensitivity-risk of terrestrial ecosystems to MPs-posed potential impacts was presented. The risk metrics based on soil-dwelling organism responses-derived biomarkers that could identify whether study regions have sensitivity-risk to MPs were developed. The recently published datasets covering geographic areas worldwide with toxicity endpoints from major soil organism groups (snail, potworm, springtail, nematode, and earthworm) were used to build relationships between species physiological alterations and MPs based on a toxicodynamic-based dose–response model. The regional pollution and species sensitivity distributions combined with a probabilistic risk model were used to compare relative ranks with MPs-associated risks using predicted thresholds. The results found that ecologically sensitive regions with severe responses to soil MPs appeared in areas polluted by sewage sludge and plastic mulching. The results also showed that ~25% of study regions suffered significant MPs-associated ecological risks. This work provides a baseline measurement tool of soil species biomarker-based thresholds for comparing regional sensitivity-risk that highlights why some regions appear to be more sensitive than others and what potential risk impact this has on MPs-polluted terrestrial ecosystems globally.

Complex Bilateral Interactions Determine the Fate of Polystyrene Micro- and Nanoplastics and Soil Protists: Implications from a Soil Amoeba.

Nano- and microplastics have become a serious global concern, threatening our living environments. Previous studies have shown that many organisms, including bacteria, animals, and plants, can be affected by microplastics. However, little is known about one ecologically important group of soil organisms, the protists. In this study, we investigated how polystyrene micro- and nanoplastics interacted with a soil amoeba Dictyostelium discoideum. The results showed that environmental concentrations of nano- and microplastics could negatively affect the soil amoeba's fitness and development. D. discoideum ingested both nano- and microplastics through phagocytosis but packed and excreted them during slug migration, which also promoted their biodegradation. Fourier transform infrared spectroscopy analyses revealed the formation of new oxygen-containing functional groups and the sign of possible oxidation of polystyrene. Also, nano- and microplastic exposure disrupted the nutrient and energy metabolisms of D. discoideum and affected the expression of key genes (e.g., cf45-1, dcsA, aprA, dymB, and gefB) related to morphogenesis and phagocytosis. In conclusion, our results show that nano- and microplastics have complex bilateral interactions with the soil amoeba, affecting each other's fate in the soil environment. This study provides new insights into how soil protists interact with nano- and microplastics in the soil ecosystem.

Changes in soil faunal density and microbial community under altered litter input in forests and grasslands

Root and foliar litter inputs are the primary sources of carbon and nutrients for soil fauna and microorganisms, yet we still lack a quantitative assessment to evaluate the effects of root and foliar litter on various groups of soil organisms across terrestrial ecosystems. Here, we compiled 978 paired observations from 68 experimental sites to assess the directions and magnitudes of adding and removing foliar and root litter on the soil faunal density and microbial biomass that was evaluated by phospholipid fatty acids (PLFAs) across forests and grasslands worldwide. We found that litter addition had only a marginal effect on soil faunal density but significantly increased the soil total microbial-, fungal- and bacterial-PLFAs by 13%, 14%, and 10%, respectively, across ecosystems, suggesting that the soil microbial community is more sensitive to carbon source addition than soil fauna, particularly in soils with low carbon to nitrogen ratios. In contrast, removing litter significantly decreased the soil faunal density by 17% but had few effects on soil microorganisms. Compared with foliar litter, root litter input had a more positive effect on the development of soil fungal taxa. The effect of both litter addition and removal on soil faunal density and microbial biomass did not differ between humid and arid regions, but a greater influence was observed in grasslands than in forests for soil microbial community. Our results highlight that the increasing litter production under a global greening scenario would stimulate microbial activity in grasslands more than in forests, and this stimulation would be greater for soil microbes than soil fauna.

Impact of biocontrol microbes on soil microbial diversity in ginger (Zingiber officinale Roscoe).

Bacteria are the most diverse and abundant group of soil organisms that influence plant growth and health. Bacillus and Trichoderma are commonly used as biological control agents (BCA) that directly or indirectly act on soil bacteria. Therefore, it is essential to understand how the applied microbes impact the indigenous microbial community before exploring their activity in the control of soilborne diseases. MiSeq sequencing of the 16S rRNA gene was used to decipher the shift of rhizosphere bacterial community in ginger (Zingiber officinale Roscoe) treated with Bacillus subtilus and Trichoderma harzianum at different concentrations. The dominant phyla in treated and nontreated samples were Proteobacteria, Actinobacteria, Acidobacteria and comprised up to 54.7% of the total sequences. There were significant differences between BCA treated and nontreated samples in the bacteria community. BCA treated plants presented higher bacterial diversity than nontreated and higher dosage of BCA had a larger impact on rhizosphere microbiota, but the 'dose-response relationship' varied in different bacterial groups. Potential biomarkers at genus level were found, such as RB41, Pseudomonas, Nitrospira, Candidatus_Udaeobacter. The combined use of Bacillus subtilus and Trichoderma harzianum could alter bacterial community structure and diversity in rhizosphere soil. BCA-microbes interactions as well as soil microbial ecology should be noticed in plant disease management. © 2021 Society of Chemical Industry.

Predictors of soil fungal biomass and community composition in temperate mountainous forests in Central Europe

Fungi are a highly diverse group of soil organisms greatly contributing to the functioning of forest ecosystems. Consequently, the understanding of factors affecting their productivity and distribution is needed for the understanding of litter and soil ecology. While several drivers of fungal community composition have been identified, it is less clear how their relative importance depends on topsoil habitats and how consistent it is across fungal ecological guilds. Moreover, the predictors of fungal biomass are much less known than those of the community composition. To fill these knowledge gaps, we collected and analyzed a comprehensive dataset from a Central European coniferous forest, covering a broad range of elevations and vegetation types and spanning from managed forests to protected forests with minimal human intervention. Fungal standing biomass and composition (including root, soil and litter habitats) was analyzed in relation to site characteristics, soil and litter chemistry and vegetation (intense botanical surveys and molecular analysis of plant roots). We found that fungal biomass and community composition in soil were vertically stratified in our study area. The nutrient-rich litter contained elevated fungal biomass content and it was dominated by saprotrophic fungi, whereas bulk soil, with less fungal biomass, was dominated by ECM fungi and relatively depleted of saprotrophs. We show that vegetation was a key predictor of fungal community composition across all ecological guilds of fungi and habitats. pH of soil or litter was a significant predictor of fungal community composition in all studied habitats, whereas climatic (altitude) effects were observed for fungal biomass and composition in bulk soil. Finally, P was the most important nutrient in our study, explaining >20% of variance in fungal biomass and affecting fungal community composition across habitats. Our results support the idea that intense atmospheric deposition of N during last decades may have shifted Central European forests from N-limitation to P-limitation. In light of increased global anthropogenic N inputs projected for the next century, our results suggest that fungal productivity might become P-limited rather than N-limited in temperate forests.

Faster recovery of soil biodiversity in native species mixture than in Eucalyptus monoculture after 60years afforestation in tropical degraded coastal terraces.

Afforestation is an effective method to restore degraded land. Afforestation methods vary in their effects on ecosystem multifunctionality, but their effects on soil biodiversity have been largely overlooked. Here, we mapped the biodiversity and functioning of multiple soil organism groups resulting from diverse afforestation methods in tropical coastal terraces. Sixty years after afforestation from bare land (BL), plant species richness and the abundance of plant litter (398±85gm-2 ) and plant biomass (179±3.7tha-1 ) in native tree species mixtures (MF) were restored to the level of native forests (NF; 287±21gm-2 and 243.0±33tha-1 , respectively), while Eucalyptus monoculture (EP) only successfully restored the litter mass (388±43gm-2 ) to the level of NF. Soil fertility in EP and MF was increased but remained lower than in NF. For example, soil nitrogen and phosphorus concentrations in MF (1.2±0.2gkg-1 and 408±49mgkg-1 , respectively; p<0.05) were lower than in NF (1.8±0.2gkg-1 and 523±24mgkg-1 , respectively; p<0.05). Soil biodiversity, abundance (except for nematodes), and community composition in MF were similar or greater than those in NF. In contrast, restoration with EP only enhanced the diversity of microbes and mites to the level of NF, but not for other soil biota. Together, afforestation with native species mixtures can end up restoring vegetation and most aspects of the taxonomic and functional biodiversity in soil whereas monoculture using fast-growing non-native species cannot. Native species mixtures show a greater potential to reach completely similar levels of soil biodiversity in local natural forests if they are received some more decades of afforestation. Multifunctionality of soil biotic community should be considered to accelerate such processes in future restoration practices.

Medium-term response of the natural grassland soil biota to multiwalled carbon nanotube contamination

Although the soil environment can potentially be exposed to contamination by carbon nanotubes (CNT), its impact on soil biology is poorly understood. In this study, we investigated the effect of the multiwalled CNT (MWCNT) contamination on different groups of soil organisms (microbial, micro- and mesofaunal communities) as well as the soil enzyme activity. The experimental mesocosms included the intact soil cores that were collected from a natural grassland. The MWCNTs that were pristine (pCNTs) and functionalised (fCNTs) at a concentration of 500 μg g−1 of soil were applied in the form of water suspensions to the surface of the mesocosms, while ensuring the soil was not mixed after the treatment. Soil samples were taken at 3, 6, and 15 weeks after CNT application. The CNT soil contamination highlighted differences in the community dynamics within the studied groups when compared to the control (non-contaminated soil). Among the faunal groups, nematodes were found to be more sensitive to the CNT impact than mites. The most pronounced response of the nematodes was observed in the subsoil at week 6, when their numbers were 3- (pCNTs) and 4-fold (fCNTs) higher than the control mesocosms. Both types of CNTs influenced the relative abundance of the bacterial- and hyphal-feeding nematodes, where pCNTs significantly and negatively affected the predatory nematodes. Moreover, CNTs temporarily, but significantly, decreased the diversity of the nematode communities. In addition, the values of the nematode Structure Index confirmed a strong transitional disturbance effect of CNTs in the soil food web, while the Channel Index in the pCNTs indicated an increasing share of fungi in the decomposition pathway. Hence, we can infer that although the impact of CNTs seems to be temporary, the shifts in the soil community abundance and structure that it induced may have long-term consequences for soil functioning, including nutrient cycling.

Temperature and pH define the realised niche space of arbuscular mycorrhizal fungi.

The arbuscular mycorrhizal (AM) fungi are a globally distributed group of soil organisms that play critical roles in ecosystem function. However, the ecological niches of individual AM fungal taxa are poorly understood. We collected>300 soil samples from natural ecosystems worldwide and modelled the realised niches of AM fungal virtual taxa (VT; approximately species-level phylogroups). We found that environmental and spatial variables jointly explained VT distribution worldwide, with temperature and pH being the most important abiotic drivers, and spatial effects generally occurring at local to regional scales. While dispersal limitation could explain some variation in VT distribution, VT relative abundance was almost exclusively driven by environmental variables. Several environmental and spatial effects on VT distribution and relative abundance were correlated with phylogeny, indicating that closely related VT exhibit similar niche optima and widths. Major clades within the Glomeraceae exhibited distinct niche optima, Acaulosporaceae generally had niche optima in low pH and low temperature conditions, and Gigasporaceae generally had niche optima in high precipitation conditions. Identification of the realised niche space occupied by individual and phylogenetic groups of soil microbial taxa provides a basis for building detailed hypotheses about how soil communities respond to gradients and manipulation in ecosystems worldwide.

Soil biota suppress maize growth and influence root traits under continuous monoculture

This study investigated maize-soil biota interactions as well as the soil legacy effects of continuous monoculture (CM) on maize performance. We conducted a glasshouse experiment that compared the performance of maize inoculated with living or sterilized soil inocula collected from experimental field plots with cropping histories of 1 to 5 years of continuous maize monoculture, where the soil type is Nicollet clay loam with moderate fertility. We measured the biomass, yield, root traits and leaf nutrients of maize as well as eukaryotic soil organisms. Inoculation with living soil dramatically reduced maize biomass and yield compared to inoculation with sterilized soil, showing CM to have strong negative soil biotic legacy effects on maize. Nonetheless, the strength of soil biotic effects on most maize variables were relatively stable over time under CM. The response of maize total biomass to living soil inoculation correlated positively with arbuscular mycorrhizal (AM) fungal abundance but negatively with soil fauna abundance, whereas it did not relate with the abundance of plant pathogenetic fungi or herbivorous nematodes. The roots showed acquisitive syndromes (high specific root length but low root diameter) in sterilized soil but conservative syndromes (opposite traits) in living soil. The responses in root system structure were tightly related with AM fungal diversity and community composition. Our study shows strong and stable negative effects of soil biota on maize under CM. The complex effects of soil biota on maize performance highlight the need to explore the functions of different groups of soil organisms to better understand and control negative soil legacy effects in agroecosystems.

Divergent effects of drought and nitrogen deposition on microbial and arthropod soil communities in a Mediterranean forest

Drivers of global change such as warming and increased nitrogen (N) availability are altering soil communities worldwide, with unknown consequences for the functioning of the terrestrial ecosystems. Higher N availability may stimulate soil communities and boost nutrient cycling, but the expected increase in aridity may nullify this effect. Additionally, shifts in microbial communities may lead to trophic cascades throughout soil food webs, affecting key ecosystem properties associated with the turnover of carbon and nutrients. Whether the responses to these different drivers of global change are similar between the main guilds of soil organisms, however, is unclear. We analyzed soil phospholipid fatty acids and extracted soil fauna to determine the simultaneous responses of microbial and arthropod soil communities to experimental drought and increased N availability in a Mediterranean forest. The experimental drought decreased community sizes across the entire soil food web, and N addition increased the biomass of all microbial groups except fungi, thereby increasing the relative dominance of bacteria. Likewise, the abundance of oribatid mites strongly increased after the addition of N, whereas the population of springtails quickly decreased, leading to a shift in the structure of the arthropod community. An increase in soil N availability promoted the energy channel dominated by bacteria, triggering a bottom-up trophic cascade affecting the arthropod mesofauna, thus propagating the effects of N inputs throughout the soil food web. The strong constraint of drought on soil microbes, however, may neutralize the effect of an increase in N availability. Complex interactions among factors of global change may therefore hinder our ability to predict their effects on soil biodiversity and associated consequences for ecosystem functioning. Forecasts of responses of soil biodiversity to global change should not only consider different drivers and their potential interactions, but also the likely contrasting effects among different groups of soil organisms.

Soil textural heterogeneity impacts bacterial but not fungal diversity

Soils harbour high levels of microbial diversity, underpinning their ability to provide key soil functions and ecosystem services. The extreme variety of soil microbial life is often explained by reference to the physical and chemical heterogeneity of the soil environment. However, detailed understanding of this link is still lacking, particularly as micro-scale studies are difficult to scale up to the soil profile or landscape level. To address this, we used soil samples collected from a wide range of temperate oceanic habitats (e.g. arable, grassland, coniferous and deciduous woodland, heathland; 335 sites in total) to evaluate the link between soil texture and microbial diversity. Soil particle size distribution was measured in each sample using laser granulometry (i.e. sand, silt, clay), while the diversity of bacterial and fungal communities were determined by metabarcoding with an Illumina MiSeq using16S and ITS1 taxonomy marker gene regions, respectively. Multifractal analysis of the soil particle size distribution was then used to describe the heterogeneity of the soil particle sizes. Overall, our results showed no impact of habitat type upon textural heterogeneity indicating that it is an aspect of soil quality resistant to management decisions. Using a structural equation modelling approach, we show that soil textural heterogeneity positively influences bacterial diversity but had little impact upon fungal diversity. We also find that textural composition impacts both bacterial and fungal composition, with many specific microbial taxa showing co-occurrence relationships with clay and fine-silt sized particles. Our results strongly indicate that soil textural heterogeneity influences microbial community diversity regardless of soil management practices and biophysical activities. The close linkages between different groups of soil organisms can obscure the mechanisms driving the development of biodiversity, however, it is clear that the soil physical environment has differential impacts on organisms with different life history strategies.

Soil Nematode Fauna and Microbial Characteristics in an Early-Successional Forest Ecosystem

Windstorms can often decrease the diversity of native local biota in European forests. The effects of windstorms on the species richness of flora and fauna in coniferous forests of natural reserves are well established, but the effects on biotas in productive deciduous forests have been less well studied. We analyzed the impact of windstorms on the diversity and abundance of soil nematode communities and microbial activity and their relationships with the succession of plant species and basic soil physicochemical properties 12 and 36 months after a windstorm in Fagus sylvatica forests. The relationships were investigated in cleared early-successional forest ecosystems and at undamaged forest sites as a control. The windstorm significantly affected total nematode abundance, number of nematode species, and the diversity and abundance of all nematode functional guilds, but no functional guilds disappeared after the disturbance. The abundance of several nematode taxa but not total nematode abundance was positively correlated with soil-moisture content. Indices of the nematode communities were inconsistent between sites due to their variable ability to identify ecosystem disturbance 12 months after the storm. In contrast, the metabolic activity of various functional groups identified ecosystem disturbance well throughout the study. Positive correlations were identified between the number of plant parasites and soil-moisture content and between carnivore abundance and soil pH. Positive mutual links of some nematode genera (mainly plant parasites) with the distribution of dominant grasses and herbs depended on the habitat. In contrast, microbial activity differed significantly between disturbed and undisturbed sites up to 36 months after the storm, especially soil basal respiration, N mineralization, and microbial biomass. Our results indicated different temporal responses for two groups of soil organisms to the destruction of the tree canopy. Soil nematodes reacted immediately, but changes in the microbial communities were visible much later after the disturbance.