Search

Summary: Arbuscular mycorrhizal fungi (AMF) are ubiquitous plant root symbionts, which can house two endobacteria: Ca. Moeniiplasma glomeromycotorum (CaMg) and Ca. Glomeribacter gigasporarum (CaGg). However, little is known about their distribution and population structure in natural AMF populations and whether AMF can harbour other endobacteria.We isolated AMF from two environments and conducted detailed analyses of endobacterial communities associated with surface‐sterilised AMF spores.Consistent with the previous reports, we found that CaMg were extremely abundant (80%) and CaGg were extremely rare (2%) in both environments. Unexpectedly, we discovered an additional and previously unknown level of bacterial diversity within AMF spores, which extended beyond the known endosymbionts, with bacteria belonging to 10 other phyla detected across our spore data set. Detailed analysis revealed that: CaGg were not limited in distribution to the Gigasporaceae family of AMF, as previously thought; CaMg population structure was driven by AMF host genotype; and a significant inverse correlation existed between the diversity of CaMg and diversity of all other endobacteria.Based on these data, we generate novel testable hypotheses regarding the function of CaMg in AMF biology by proposing that they might act as conditional mutualists of AMF. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) provide plants with vital mineral nutrients and co‐exist inside the roots alongside a complex community of bacterial endophytes. These co‐existing AMF and bacterial root communities have been studied individually and are known to be influenced in structure by different environmental parameters. However, the extent to which they are affected by environmental parameters and by each other is completely unknown. The current study addressed this knowledge gap by characterising AMF and bacterial communities inside plant roots from a natural and an agricultural ecosystem. Using multivariate modelling, the relative contribution of environmental parameters in structuring the two communities was quantified at different spatial scales. Using this model, it was possible to then remove the contribution of environmental parameters and show that the co‐existing AMF and bacterial communities were significantly correlated with each other, explaining up to 36% of each other's variance. Notably, this was not due to the presence of know AMF endobacteria, as removal of endobacterial reads maintained the significance of correlation. These findings provide the first empirical evidence of a selective and bi‐directional relationship between AMF and bacteria co‐inhibiting plant roots and indicate that a significant fraction of this covariation is due to biological and ecological interactions between them. [ABSTRACT FROM AUTHOR]

Sex is evolutionarily more costly than parthenogenesis, evolutionary ecologists therefore wonder why sex is much more frequent than parthenogenesis in the majority of animal lineages. Intriguingly, parthenogenetic individuals and species are as common as or even more common than sexuals in some major and putative ancient animal lineages such as oribatid mites and rotifers. Here, we analyzed oribatid mites (Acari: Oribatida) as a model group because these mites are ancient (early Paleozoic), widely distributed around the globe, and include a high number of parthenogenetic species, which often co‐exist with sexual oribatid mite species. There is evidence that the reproductive mode is phylogenetically conserved in oribatid mites, which makes them an ideal model to test hypotheses on the relationship between reproductive mode and species' ecological strategies. We used oribatid mites to test the frozen niche variation hypothesis; we hypothesized that parthenogenetic oribatid mites occupy narrow specialized ecological niches. We used the geographic range of species as a proxy for specialization as specialized species typically do have narrower geographic ranges than generalistic species. After correcting for phylogenetic signal in reproductive mode and demonstrating that geographic range size has no phylogenetic signal, we found that parthenogenetic lineages have a higher probability to have broader geographic ranges than sexual species arguing against the frozen niche variation hypothesis. Rather, the results suggest that parthenogenetic oribatid mite species are more generalistic than sexual species supporting the general‐purpose genotype hypothesis. The reason why parthenogenetic oribatid mite species are generalists with wide geographic range sizes might be that they are of ancient origin reflecting that they adapted to varying environmental conditions during evolutionary history. Overall, our findings indicate that parthenogenetic oribatid mite species possess a widely adapted general‐purpose genotype and therefore might be viewed as "Jack‐of‐all‐trades." [ABSTRACT FROM AUTHOR]

Ecologists have long debated the properties that confer stability to complex, species-rich ecological networks. Species-level soil food webs are large and structured networks of central importance to ecosystem functioning. Here, we conducted an analysis of the stability properties of an up-to-date set of theoretical soil food web models that account both for realistic levels of species richness and the most recent views on the topological structure (who is connected to whom) of these food webs. The stability of the network was best explained by two factors: strong correlations between interaction strengths and the blocked, nonrandom trophic structure of the web. These two factors could stabilize our model food webs even at the high levels of species richness that are typically found in soil, and that would make random systems very unstable. Also, the stability of our soil food webs is well-approximated by the cascade model. This result suggests that stability could emerge from the hierarchical structure of the functional organization of the web. Our study shows that under the assumption of equilibrium and small perturbations, theoretical soil food webs possess a topological structure that allows them to be complex yet more locally stable than their random counterpart. In particular, results strongly support the general hypothesis that the stability of rich and complex soil food webs is mostly driven by correlations in interaction strength and the organization of the soil food web into functional groups. The implication is that in real-world food web, any force disrupting the functional structure and distribution pattern of interaction strengths (i.e., energy fluxes) of the soil food webs will destabilize the dynamics of the system, leading to species extinction and major changes in the relative abundances of species. [ABSTRACT FROM AUTHOR]

Agricultural intensification is a major driver of biodiversity loss, with the implementation of Agri‐Environment Schemes (AESs) being a widespread policy designed to prevent further loss, and to maintain or restore ecosystem health. Upland grassland soils are disproportionately impacted by intensification including drainage, artificial fertiliser use, compaction and erosion while the effect of AES management on below‐ground microarthropods, which mediate a range of ecosystem processes, is largely unknown.This study tested the effects of AES management of upland grasslands on microarthropod communities using a large‐scale factorial field experiment. The study focused on microarthropods with distinct taxa‐specific responses observed.Oribatid mite abundance was associated with wetter, more extensive pastures with native grasses characteristic of semi‐improved grassland managed by AESs, whereas Collembola abundance was associated with drier, more intense, reseeded (Lolium perenne dominated) pastures characteristic of conventionally managed improved grasslands.Differences in taxa responses may be driven by life‐history traits and resilience to disturbance. There was no net effect of management, habitat or their interaction on total microarthropod family diversity or abundance.Synthesis and Applications. Results from this study suggest that in floristically simple upland agroecosystems the impact of agri‐environment measures on below‐ground soil biota are context‐dependent (differing between contrasting grassland types), and taxa‐specific, rather than leading to general increases in biodiversity per se, and the responses of soil microarthropods are driven by environmental variation caused by overall management of grassland fields. Measures should aim to increase the availability of areas of semi‐improved grassland, with native plant mixtures, adjacent to improved grasslands, to maximise the habitats available to soil microarthropods. [ABSTRACT FROM AUTHOR]

Carrion is a frequent but overlooked source of nutrients to the soil. The decomposition of carrion is accelerated by invertebrate scavengers, but the impact of the scavengers on below‐ground biota and its functions is scarcely known.We conducted a laboratory experiment to investigate the effects of the burying beetle Nicrophorus vespilloides on the soil community of a temperate broadleaved forest. We assembled microcosms from soil collected from an oak woodland and treated them with mouse Mus musculus carcasses and mating pairs of burying beetles (♀+♂) in a factorial design with control soils. We sampled independent replicates over time to investigate how the beetles affect soil microarthropods and microbial biomass (bacteria and fungi) in relation to soil pH and organic matter content.The beetle treatment initially reduced the total microbial biomass and abundance of major groups of microarthropods relative to the control soil. At the same time, organic matter increased in the beetle treatment and then dropped to the pre‐beetle level (i.e. soil baseline) at the end of the beetle breeding cycle (2 weeks). The rapid temporal changes in organic matter were mimicked by the relative abundances of the dominant microarthropod groups, with Oribatida relatively more abundant than Collembola and predaceous mites in the beetle treatment. The overall final effect of the beetle (relative to the laboratory control) on microarthropods was negative but the beetle kept these variables within the levels observed for freshly collected soil (baseline), while the final effect on pH was positive, and most likely driven by the surplus of nutrients from the carcass and biochemical changes triggered by the decomposition process.In nature, scavenging invertebrates are widespread. Our study demonstrates that beetles breeding in carcasses regulate the dynamics of key components of the soil food web, including microbial biomass, changes in the relative abundances of dominant microarthropods and soil organic matter and pH. Given the abundance of these beetles in nature, the study implies that the distribution of these beetles is a key driver of variation in soil nutrient cycling in woodlands. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

• Both Mesostigmata adult and juvenile abundance increased under warming. • Mesostigmata assemblages shifted and average individual body mass increased. • Assemblages shifted due to the increased abundances of parthenogenetic species. • These results align with previous studies on Oribatida assemblages under warming. Increasing global mean surface temperatures from climate change will coincide with longer and more frequent short-term, extreme warming events. Because of this, habitats like boreal forests are predicted to have new temperature regimes. Boreal forest soils contain a diverse array of microarthropods and nematodes, which include the main soil predators, mesostigmatic mites (Acari: Parasitiformes: Mesostigmata). Although extensive research exists on how climate warming affects oribatid mite and collembolan communities, fewer studies have examined how warming effects Mesostigmata communities. We tested the effect of short-term (three months), intensive warming (+8 °C) on Mesostigmata communities from the boreal forest using experimental mesocosms containing forest-floor material. We collected moss mats and underlying forest floor organic material from a boreal forest and incubated them within individual mesocosms at 12 °C and 20 °C for three months, where 12 °C represented the long-term average growing season temperature and 20 °C corresponds to the potential extreme surface temperature from climate warming for the region. We enumerated all extracted microarthropods and nematodes, and identified all Mesostigmata adults to the species-level. In total, we counted 24,080 nematode individuals, and 19,582 total microarthropod individuals, of which 3349 individuals (1899 adults and 1450 juveniles) were mesostigmatic mites, consisting of 14 species. Mesostigmatic juvenile and adult abundances, along with adult community-level body mass were higher under warming, which lead to a shift in community composition. Changes to Mesostigmata communities were driven by the greater abundances of parthenogenetic species, primarily Veigaia mitis (Berlese), under warming—a response that has been shown in oribatid mite communities, but not mesostigmatic communities, before. Overall, we found that warming shifted mesostigmatic mite communities in the boreal forest, which has wide ranging implications for the soil food web. [ABSTRACT FROM AUTHOR]

There is an increasing interest in understanding how soil microbial communities respond to perturbations associated with global change. Much of the currently available knowledge is based on controlled laboratory experiments, large scale surveys and manipulative studies in which one perturbation, for example drought, is applied under a range of conditions. Until now, emphasis has been on spatial replication of experimental units and the quantification of variation in soil microbial community structure, and its correlation to ecosystem-level variables such as gas fluxes. But microbial communities naturally fluctuate over time, their response to perturbations is temporal, and they generally experience multiple perturbations simultaneously and/or in a variable sequence, such as spells of drought alternating with flooding events. Furthermore, variation in the soil microbial community in response to perturbations may not directly reflect the overall expression of functions of a microbial community. Here, we identify three experimental challenges that we refer to as the variance , locality and structure challenge. We briefly synthesise the state of the art around these three challenges to open a discussion on the many experimental issues ecologists face when measuring the effects of perturbations on the structure and functions of soil microbial communities in time and space. We propose experimental, sampling and modelling strategies that can help resolve the experimental challenges discussed in this paper. [ABSTRACT FROM AUTHOR]

Common mycorrhizal networks (CMNs) are an enigmatic feature of soil and mycorrhizal ecology. The current use of the term ‘common mycorrhizal network’ stipulates a direct, continuous physical link between plants formed by the mycelium of mycorrhizal fungal genets. This means that a specific case (involving hyphal continuity) is used to define a much broader phenomenon of hyphae interlinking among roots of different plants. We here embrace a more inclusive definition of the CMN as a network formed by mycorrhizal fungal genets among roots of different plants, irrespective of the type of connection or interaction, and not limited to direct hyphal linkages. Implicitly, this broader version of the term has been used by many researchers already. We propose using the term ‘common mycorrhizal networks with hyphal continuity’ (CMN‐HC) to capture the more specific case of a continuous link via hyphae between the roots of different plants, which is important to study for some (notable carbon and nutrient exchange), but not all functions of a CMN (e.g. transfer of infochemicals or microbes). In addition, and becoming more general than CMN, we introduce the term ‘common fungal network’ (CFN) to include networks of any type of connection formed between different plants by any type of fungus; this includes also non‐mycorrhizal fungi, and indeed a combination of non‐mycorrhizal and mycorrhizal networks. We assert that this new conceptual framework incorporating three hierarchical terms (CMN‐HC, CMN and CFN), ranging from the most specific to the very broad, can usher in a period of new research activity on fungal networks. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Swidden agriculture is a widespread subsistence farming method in the tropics, which is being intensified as human populations grow. This study is the first to investigate the impacts of land degradation from swidden upon ant species (both native and introduced) across the full degradation gradient, from forest, to tree fallows, to shrub fallows, to exhausted land. Ant communities in closed canopy forests had higher species diversity and were taxonomically distinct, but as land became increasingly degraded, a significant reduction in overall and native species richness was detected, as were changes in overall community composition. Whilst native species decreased across the degradation gradient, introduced species increased. There was also a significant correlation in community compositional changes between native and introduced species which was independent from environmental factors. Co-occurrence analysis, however, suggested there was little evidence that introduced species were significantly impacting the communities of native species. This suggests these patterns are both separately driven by habitat degradation. Degraded fallow habitats were found to harbour unique and endemic species, including 22.4% of the species found in closed canopy forest. Together, our results highlight the potentially detrimental effects of further spread and increased intensification of swidden systems in tropical ecosystems. The conservation of existing closed canopy forests is of utmost importance but we also highlight that the fauna of degraded swidden habitats could still be important for biodiversity conservation in agricultural landscapes across the tropics. • Ant communities in forests were species rich and compositionally unique. • Increased degradation led to species richness declines and composition changes. • Increased degradation also increased the prevalence of introduced ant species. • Degraded habitats are not devoid of species and could play a role for conservation. [ABSTRACT FROM AUTHOR]