The role of active movement in fungal ecology and community assembly

Movement ecology aims to provide common terminology and an integrative framework of movement research across all groups of organisms. Yet such work has focused on unitary organisms so far, and thus the important group of filamentous fungi has not been considered in this context. With the exception of spore dispersal, movement in filamentous fungi has not been integrated into the movement ecology field. At the same time, the field of fungal ecology has been advancing research on topics like informed growth, mycelial translocations, or fungal highways using its own terminology and frameworks, overlooking the theoretical developments within movement ecology. We provide a conceptual and terminological framework for interdisciplinary collaboration between these two disciplines, and show how both can benefit from closer links: We show how placing the knowledge from fungal biology and ecology into the framework of movement ecology can inspire both theoretical and empirical developments, eventually leading towards a better understanding of fungal ecology and community assembly. Conversely, by a greater focus on movement specificities of filamentous fungi, movement ecology stands to benefit from the challenge to evolve its concepts and terminology towards even greater universality. We show how our concept can be applied for other modular organisms (such as clonal plants and slime molds), and how this can lead towards comparative studies with the relationship between organismal movement and ecosystems in the focus

Basic principles of temporal dynamics

All ecological disciplines consider temporal dynamics, although relevant concepts have been developed almost independently. We here introduce basic principles of temporal dynamics in ecology. We figured out essential features that describe temporal dynamics by finding similarities among about 60 ecological concepts and theories. We found that considering the hierarchically nested structure of complexity in temporal patterns (i.e. hierarchical complexity) can well describe the fundamental nature of temporal dynamics by expressing which patterns are observed at each scale. Across all ecological levels, driver–response relationships can be temporally variant and dependent on both short- and long-term past conditions. The framework can help with designing experiments, improving predictive power of statistics, and enhancing communications among ecological disciplines

Effect of different root endophytic fungi on plant community structure in experimental microcosms

Understanding the effects of root-associated microbes in explaining plant community patterns represents a challenge in community ecology. Although typically overlooked, several lines of evidence point out that nonmycorrhizal, root endophytic fungi in the Ascomycota may have the potential to drive changes in plant community ecology given their ubiquitous presence, wide host ranges, and plant species-specific fitness effects. Thus, we experimentally manipulated the presence of root endophytic fungal species in microcosms and measured its effects on plant communities. Specifically, we tested whether (1) three different root endophyte species can modify plant community structure; (2) those changes can also modified the way plant respond to different soil types; and (3) the effects are modified when all the fungi are present. As a model system, we used plant and fungal species that naturally co-occur in a temperate grassland. Further, the soil types used in our experiment reflected a strong gradient in soil texture that has been shown to drive changes in plant and fungal community structure in the field. Results showed that each plant species responded differently to infection, resulting in distinct patterns of plant community structure depending on the identity of the fungus present. Those effects depended on the soil type. For example, large positive effects due to presence of the fungi were able to compensate for less nutrients levels in one soil type. Further, host responses when all three fungi were present were different from the ones observed in single fungal inoculations, suggesting that endophyte–endophyte interactions may be important in structuring plant communities. Overall, these results indicate that plant responses to changes in the species identity of nonmycorrhizal fungal community species and their interactions can modify plant community structure

Arbuscular mycorrhizal fungal hyphae reduce soil erosion by surface water flow in a greenhouse experiment

This research was funded by the SMART Joint Doctoral Programme (Erasmus Mundus Programme of the European Union) and the DRS HONORS Fellowship programme of Freie Universität Berlin. This study is a contribution to an EU Marie Curie Career Integration Grant to T.C. (EC FP7-631399-SENSE

Microplastic incorporation into soil in agroecosystems

Background: We live in a plastic age (Thompson et al., 2009), with microplastic (typically defined as plastic particles < 5 mm) becoming an increasingly appreciated aspect of environmental pollution. Research has been overwhelmingly focused on aquatic systems, especially the oceans, but there is a current shift to more strongly consider terrestrial ecosystems (Rillig, 2012; Horton et al., 2017). In particular agroecosystems are coming into focus as a major entry point for microplastics in continental systems (Nizzetto et al., 2016b), where contamination might occur via different sources as sludge amendment or plastic mulching (Steinmetz et al., 2016). Given the central role of agroecosystems, including their soil biodiversity (Rillig et al., 2016), in food production, such numbers are potential cause for concern. Field data on measured microplastic presence in agricultural soils are still not widely available, but nevertheless this material is certain to arrive at the soil surface. The fate of material deposited at the soil surface is not clear: particles may be removed by wind or water erosion, becoming airborne, or may be lost by surface runoff (Nizzetto et al., 2016a). Nevertheless, a substantial part of the microplastic (or nanoplastic following further disintegration) is expected to enter the soil. The degree of hazard represented by microplastic to various soil biota is not clear. Direct evidence comes from experimental work on earthworms, on which microbeads had negative effects (Huerta Lwanga et al., 2016; also reviewed in Horton et al., 2017). Data on impacts on other soil biota groups are not available. However, Kiyama et al. (2012) have shown that polystyrene beads can be taken up by the nematode Caenorhabditis elegans; this means the material could also accumulate in the soil food web (Rillig, 2012). Movement into soil is an important aspect of assessing risk: will soil biota be exposed to microplastics? Here, we sketch what is known about movement of such particles in soil, which players and factors could influence this, and we chart avenues for research aimed at the movement and distribution of microplastic in agricultural soils

Deciphering the relative contributions of multiple functions within plant-microbe symbioses

This is the publisher's version, also available electronically from http://www.esajournals.org/doi/abs/10.1890/09-1858.1For microbial symbioses with plants, such as mycorrhizas, we typically quantify either the net effects of one partner on another or a single function a symbiont provides. However, many microbial symbioses provide multiple functions to plants that vary based on the microbial species or functional group, plant species, and environment. Here we quantified the relative contributions of multiple functions provided by arbuscular mycorrhizal (AM) fungi to symbiont-mediated changes in plant biomass. We used two published data sets, one that measured multiple functions (pathogen protection and nutrient uptake) on a single plant and one that measured a single function (pathogen protection) on multiple plants. Using structural equation modeling, we observed strong variation in the functional pathways by which AM fungi altered plant growth; changes in plant biomass were associated with different functions (and different AM fungal functional groups) for the different plant species. Utilizing this methodology across multiple partners and environments will allow researchers to gauge the relative importance of functions they isolate and, perhaps more importantly, those they did not consider. This baseline information is essential for establishing the specific mechanisms by which microbial symbioses influence plant diversity and to more effectively utilize these organisms in agriculture, restoration and conservation

Sub-lethal fungicide concentrations both reduce and stimulate the growth rate of non-target soil fungi from a natural grassland

Conventional agriculture has relied extensively on the use of fungicides to prevent or control crop diseases. However, some fungicides, particularly broad-spectrum fungicides, not only eliminate target pathogens but also non-target and beneficial soil microbes. This scenario is not only limited to agricultural soil, but this may also potentially occur when neighboring environments are contaminated by fungicides through spray drift. Although concentrations may be sub-lethal, the chemicals may accumulate in the soil when used continuously resulting in more toxic effects. In this study, the effect on the colony extension rate of 31 filamentous soil saprobic fungi, initially isolated from a protected grassland ecosystem, were analyzed under fungicide treatment. These isolates were considered naive (no deliberate exposure), hence presumed to have not developed resistance. Two currently used fungicides with different modes of action were added to Potato Dextrose Agar at varying concentrations. Results showed a wide range of tolerance and sensitivity to isopyrazam and prothioconazole. Fungi belonging to the phylum Basidiomycota were most negatively affected by both fungicides. Phylum Mucoromycota were the most tolerant to prothioconazole while isolates belonging to phylum Ascomycota differed in their responses to both fungicides. Negative effects on the growth rate were more pronounced at higher concentrations except for a few isolates that were inhibited at 1 mg·L−1. A slightly positive effect was also observed in three of the isolates under fungicide treatment. Lastly, the negative impact of fungicides was not associated with the growth strategy of the fungi, whether fast growing or slow growing, rather it is isolate-specific and phylogenetically conserved. The results of this study demonstrate that co-occurring fungi differ in their sensitivity to fungicides even without prior exposure. This difference in sensitivity among co-occurring fungi may result in shifts in community composition of the soil fungal community to the detriment of the more sensitive isolates

Evolutionary implications of microplastics for soil biota

This is the author accepted manuscript. The final version is available from CSIRO Publishing via the DOI in this recordMicroplastic pollution is increasingly considered to be a factor of global change: in addition to aquatic ecosystems, this persistent contaminant is also found in terrestrial systems and soils. Microplastics have been chiefly examined in soils in terms of the presence and potential effects on soil biota. Given the persistence and widespread distribution of microplastics, it is also important to consider potential evolutionary implications of the presence of microplastics in soil; we offer such a perspective for soil microbiota. We discuss the range of selection pressures likely to act upon soil microbes, highlight approaches for the study of evolutionary responses to microplastics, and present the obstacles to be overcome. Pondering the evolutionary consequences of microplastics in soils can yield new insights into the effects of this group of pollutants, including establishing ‘true’ baselines in soil ecology, and understanding future responses of soil microbial populations and communities.MR acknowledges support from the ERC Advanced Grant ‘Gradual Change’ (694368). UK received funding from the European Union's Horizon 2020 research and innovation program under Marie Skłodowska-Curie grant agreement no. 751699

Evidence for Subsoil Specialization in Arbuscular Mycorrhizal Fungi

Arbuscular mycorrhizal (AM) fungal communities are now known to vary with depth in arable land. Here we use two previously published high-throughput Illumina sequencing data sets, and compare a 52 year long chronosequence of recultivated agriculture fields after a topsoil and subsoil mixing event, with a set of undisturbed topsoil and subsoil samples from a similar field. We show that AM taxa identified as subsoil indicators are exclusively present in early stages of the chronosequence, whereas topsoil indicator taxa can be found across the chronosequence, and that similarities from the chronosequence fields to the subsoil communities decrease with time. Our results provide evidence on the ecological specialization of certain AM fungal taxa to deep soil layers

Sodium demand of microorganisms in the phyllosphere and the organic layer of a tropical montane forest in south Ecuador

Recent studies raise the hypothesis that Na shortage restricts decomposition and affects the carbon cycle in tropical forests. When Na concentrations in soils are low and the stands are far off-coast, they do not receive substantial Na inputs from the atmosphere. Since terrestrial plants have low concentrations of Na, which is not considered as an essential element, the demand of soil fauna may not be covered. Yet, in contrast to animals, little is known of Na demands of fungi and phyllosphere microorganisms. We present results from a study on Na limitation in a montane forest ecosystem in South Ecuador, which is located on the eastern cordillera of the Andes. We tested the hypotheses that (1) the study area is characterized by low Na concentrations because of low deposition rates with incident precipitation (wind directions mainly from the Amazonian Basin), (2) decomposition processes are limited by fauna and fungal Na restrictions and (3) Na is retained in the canopy because of Na limitation of microorganisms in phyllosphere. Since 1998, we measure Na fluxes in rainfall, throughfall, stemflow, litter leachate, litterfall and organic layer in a microcatchment under an undisturbed lower montane rainforest. Results reveal comparatively low Na concentrations in the ecosystem and similar Na concentrations in throughfall and stemflow. Since Na fluxes are lower with throughfall than with incident rainfall, we conclude that Na is retained in the canopy. To explore the role of the phyllosphere in Na retention we sampled leaves covered by phyllosphere microorganisms and leaves without phyllosphere cover from several tree species, which were sprayed with a NaCl solution containing 0.5 mg L-1 Na, corresponding to the Na concentration in incident rainfall in our study area. Additionally, responses of litter decomposition to Na additions and the involved interaction of soil fungi and fauna were tested in a litterbag experiment at two sites (1000 and 2000 m a.s.l.). Results revealed enhanced decomposition rates following Na additions, though only in the presence of soil fauna. These results might have future ecosystem implications, since our time series showed that total Na deposition decreased within the past 15 years from ca. 40 kg ha-1 a-1 to 10 kg ha-1 a-1, suggesting a potential role of Na in regulating ecosystem processes