Towards establishing a fungal economics spectrum in soil saprobic fungi.

Trait-based frameworks are promising tools to understand the functional consequences of community shifts in response to environmental change. The applicability of these tools to soil microbes is limited by a lack of functional trait data and a focus on categorical traits. To address this gap for an important group of soil microorganisms, we identify trade-offs underlying a fungal economics spectrum based on a large trait collection in 28 saprobic fungal isolates, derived from a common grassland soil and grown in culture plates. In this dataset, ecologically relevant trait variation is best captured by a three-dimensional fungal economics space. The primary explanatory axis represents a dense-fast continuum, resembling dominant life-history trade-offs in other taxa. A second significant axis reflects mycelial flexibility, and a third one carbon acquisition traits. All three axes correlate with traits involved in soil carbon cycling. Since stress tolerance and fundamental niche gradients are primarily related to the dense-fast continuum, traits of the 2nd (carbon-use efficiency) and especially the 3rd (decomposition) orthogonal axes are independent of tested environmental stressors. These findings suggest a fungal economics space which can now be tested at broader scales.

Dose-response curves: the next frontier in plant ecology.

A large fraction of experimental work in plant ecology, and thus also on ecosystem functioning and the delivery of ecosystem services, describes experiments that have been carried out under controlled (glasshouse) conditions. Controlled growth settings commonly sacrifice realism through, for example, reducing the densities of plant species in the pots and controlling how environmental settings such as moisture and light vary in favor of a higher mechanistic resolution, which makes these studies particularly suitable for subsequent syntheses. We explore the possibility that further integration of dose-response curves can maximize the impact of existing studies. We suggest that we can expand considerably the scope of the dose and response variables that are considered in plant ecology.

Arbuscular mycorrhizal fungi offset NH3 emissions in temperate meadow soil under simulated warming and nitrogen deposition.

Most soil ammonia (NH3) emissions originate from soil nitrogen (N) that has been in the form of exchangeable ammonium. Emitted NH3 not only induces nutrient loss but also has adverse effects on the cycling of N and accelerates global warming. There is evidence that arbuscular mycorrhizal (AM) fungi can alleviate N loss by reducing N2O emissions in N-limited ecosystems, however, some studies have also found that global changes, such as warming and N deposition, can affect the growth and development of AM fungi and alter their functionality. Up to now, the impact of AM fungi on NH3 emissions, and whether global changes reduce the AM fungi's contribution to NH3 emissions reduction, has remained unclear. In this study, we examined how warming, N addition, and AM fungi alter NH3 emissions from high pH saline soils typical of a temperate meadow through a controlled microscopic experiment. The results showed that warming significantly increased soil NH3 emissions, but N addition and combined warming plus N addition had no impact. Inoculations with AM fungi strongly reduced NH3 emissions both under warming and N addition, but AM fungi effects were more pronounced under warming than following N addition. Inoculation with AM fungi reduced soil NH4+-N content and soil pH, and increased plant N content and soil net N mineralization rate while increasing the abundance of ammonia-oxidizing bacterial (AOB) gene. Structural equation modeling (SEM) shows that the regulation of NH3 emissions by AM fungi may be related to soil NH4+-N content and soil pH. These findings highlight that AM fungi can reduce N loss in the form of NH3 by increasing N turnover and uptake under global changes; thus, AM fungi play a vital role in alleviating the aggravation of N loss caused by global changes and in mitigating environmental pollution in the future.

Symbiotic status alters fungal eco-evolutionary offspring trajectories.

Despite host-fungal symbiotic interactions being ubiquitous in all ecosystems, understanding how symbiosis has shaped the ecology and evolution of fungal spores that are involved in dispersal and colonization of their hosts has been ignored in life-history studies. We assembled a spore morphology database covering over 26,000 species of free-living to symbiotic fungi of plants, insects and humans and found more than eight orders of variation in spore size. Evolutionary transitions in symbiotic status correlated with shifts in spore size, but the strength of this effect varied widely among phyla. Symbiotic status explained more variation than climatic variables in the current distribution of spore sizes of plant-associated fungi at a global scale while the dispersal potential of their spores is more restricted compared to free-living fungi. Our work advances life-history theory by highlighting how the interaction between symbiosis and offspring morphology shapes the reproductive and dispersal strategies among living forms.

Species-area relationships in microbial-mediated mutualisms.

Symbioses involving microorganisms prevail in nature and are key to regulating numerous ecosystem processes and in driving evolution. A major concern in understanding the ecology of symbioses involving microorganisms arises in the effectiveness of sampling strategies to capture the contrasting size of organisms involved. In many mutualisms, including mycorrhizas and gut systems, hosts interact simultaneously with multiple smaller sized mutualists, the identity of which determines success for the host. This complicates quantifying the diversity of mutualisms because sampling techniques fail to capture effectively the diversity of each partner. Here we propose the use of species-area relationships (SARs) to explicitly consider the spatial scale of microbial partners in symbioses, which we propose will improve our understanding of the ecology of mutualisms.

Arbuscular mycorrhizal root colonization depends on the spatial distribution of the host plants.

Despite their ubiquity in terrestrial ecosystems, arbuscular mycorrhizal fungi (AMF) experience dispersion constraints and thus depend on the spatial distribution of the plant hosts. Our understanding of fungal-plant interactions with respect to their spatial distributions and implications for the functioning of the symbiosis remain limited. We here manipulated the location of habitat patches of Medicago lupulina in two experiments to explore the responses of AMF root colonization and extraradical hyphae. We tested the specific hypothesis that AMF-plant habitats high in connectance would stimulate root colonization and induce denser functional root colonization (colonization rate of arbuscules plus coils) because of higher propagule availability between nearby host plant patches (experiment 1). In experiment 2, we anticipated similar responses in mixed habitats of different soil fertility, namely phosphorus-fertilized or unfertilized soil, and anticipated a higher density of extraradical hyphae in the soil connecting the habitats with increased functional root colonization. In agreement with our hypothesis, we found the highest total and functional root colonization in unfragmented micro-landscapes, describing landscapes that occur within a spatial scale of a few centimeters with the AMF-plant habitats positioned adjacent to each other. In the second experiment, overdispersed micro-landscapes promoted functional root colonization. This study provides experimental evidence that the spatial distribution of habitats can determine AMF abundance at the microscale.

Direction of plant-soil feedback determines plant responses to drought.

Droughts exarcerbate Plant-soil feedbacks (PSFs) making positive PSFs more positive and negative PSFs more negative. Alterations in PSFs that droughts induce could relate to the rooting depth of the tested plants. We present some rare evidence on how a driver of global change will alter a biotic interaction.

Local stability properties of complex, species-rich soil food webs with functional block structure.

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.

Disentangling the relative importance of spatio-temporal parameters and host specificity in shaping arbuscular mycorrhizal fungus communities in a temperate forest.

Many woody and herbaceous plants in temperate forests cannot establish and survive in the absence of mycorrhizal associations. Most temperate forests are dominated by ectomycorrhizal woody plant species, which implies that the carrying capacity of the habitat for arbuscular mycorrhizal fungi (AMF) is relatively low and AMF could in some cases experience a limitation of propagules. Here we address how the AMF community composition varied in a small temperate forest site in Germany in relation to time, space, two plant host species, and also with regard to the degree to which plots were covered with AMF-associating woody species. The AMF communities in our study were non-random. We observed that space had a greater impact on fungal community composition than either time, mycorrhizal state of the close-by woody species, or the identity of the host plant. The identity of the host plant was the only parameter that modified AMF richness in the roots. The set of parameters which we addressed has rarely been studied together, and the resulting ranking could ease prioritizing some of them to be included in future surveys. AMF are crucial for the establishment of understory plants in temperate forests, making it desirable to further explore how they vary in time and space.

Soil biota shift with land use change from pristine rainforest and Savannah (Cerrado) to agriculture in southern Amazonia.

Southern Amazonia is currently experiencing extensive land use change from forests to agriculture caused by increased local and global demand for agricultural products. However, little is known about the impacts of deforestation and land use change on soil biota. We investigated two regions in southern Amazonia (rainforest and Savannah/Cerrado biomes), analysing soil biota community turnover based on 16S (Archaea and Bacteria) and 18S rRNA genes (Eukaryotes, including Fungi, Protists and Animalia) and correlating them with soil chemistry and land use intensity. We found that soil biota community structure is driven by land use change in both Cerrado and rainforest. Crop fields approximatively doubled the richness of soil Archaea, Bacteria and Protists. We propose that crop systems not only increase soil pH and fertility, but also create continued disturbance (crop seasons) that stimulates soil diversity, as predicted by the dynamic equilibrium model (DEM) and the intermediate disturbance hypothesis (IDH). Even though agricultural fields had higher soil biota richness, some taxa were suppressed by agriculture (6/31 operational taxonomic units of Archaea, 245/1790 of Bacteria, 12/74 of Animalia, 20/144 of Fungi and 25/310 of Protists). Consequently, land use change in this region should proceed with caution. In the southern Amazonia region of Brazil, current laws require farmers to keep 20%-80% pristine vegetation areas on their property. Our data support the relevance of this law: since there are unique soil taxa under native vegetation, keeping these pristine areas adjacent to the agricultural fields should maximize soil biodiversity protection in these regions.

Soil biodiversity enhances the persistence of legumes under climate change.

Global environmental change poses threats to plant and soil biodiversity. Yet, whether soil biodiversity loss can further influence plant community's response to global change is still poorly understood. We created a gradient of soil biodiversity using the dilution-to-extinction approach, and investigated the effects of soil biodiversity loss on plant communities during and following manipulations simulating global change disturbances in experimental grassland microcosms. Grass and herb biomass was decreased by drought and promoted by nitrogen deposition, and a fast recovery was observed following disturbances, independently of soil biodiversity loss. Warming promoted herb biomass during and following disturbance only when soil biodiversity was not reduced. However, legumes biomass was suppressed by these disturbances, and there were more detrimental effects with reduced soil biodiversity. Moreover, soil biodiversity loss suppressed the recovery of legumes following these disturbances. Similar patterns were found for the response of plant diversity. The changes in legumes might be partly attributed to the loss of mycorrhizal soil mutualists. Our study shows that soil biodiversity is crucial for legume persistence and plant diversity maintenance when faced with environmental change, highlighting the importance of soil biodiversity as a potential buffering mechanism for plant diversity and community composition in grasslands.

Ten simple rules for increased lab resilience.

When running a lab we do not think about calamities, since they are rare events for which we cannot plan while we are busy with the day-to-day management and intellectual challenges of a research lab. No lab team can be prepared for something like a pandemic such as COVID-19, which has led to shuttered labs around the globe. But many other types of crises can also arise that labs may have to weather during their lifetime. What can researchers do to make a lab more resilient in the face of such exterior forces? What systems or behaviors could we adjust in 'normal' times that promote lab success, and increase the chances that the lab will stay on its trajectory? We offer 10 rules, based on our current experiences as a lab group adapting to crisis.

Ozone affects plant, insect, and soil microbial communities: A threat to terrestrial ecosystems and biodiversity.

Elevated tropospheric ozone concentrations induce adverse effects in plants. We reviewed how ozone affects (i) the composition and diversity of plant communities by affecting key physiological traits; (ii) foliar chemistry and the emission of volatiles, thereby affecting plant-plant competition, plant-insect interactions, and the composition of insect communities; and (iii) plant-soil-microbe interactions and the composition of soil communities by disrupting plant litterfall and altering root exudation, soil enzymatic activities, decomposition, and nutrient cycling. The community composition of soil microbes is consequently changed, and alpha diversity is often reduced. The effects depend on the environment and vary across space and time. We suggest that Atlantic islands in the Northern Hemisphere, the Mediterranean Basin, equatorial Africa, Ethiopia, the Indian coastline, the Himalayan region, southern Asia, and Japan have high endemic richness at high ozone risk by 2100.

Myristate and the ecology of AM fungi: significance, opportunities, applications and challenges.

A recent study by Sugiura and coworkers reported the non-symbiotic growth and spore production of an arbuscular mycorrhizal (AM) fungus, Rhizophagus irregularis, when the fungus received an external supply of certain fatty acids, myristates (C:14). This discovery follows the insight that AM fungi receive fatty acids from their hosts when in symbiosis. If this result holds up and can be repeated under nonsterile conditions and with a broader range of fungi, it has numerous consequences for our understanding of AM fungal ecology, from the level of the fungus, at the plant community level, and to functional consequences in ecosystems. In addition, myristate may open up several avenues from a more applied perspective, including improved fungal culture and supplementation of AM fungi or inoculum in the field. We here map these potential opportunities, and additionally offer thoughts on potential risks of this potentially new technology. Lastly, we discuss the specific research challenges that need to be overcome to come to an understanding of the potential role of myristate in AM ecology.

Arbuscular mycorrhiza has little influence on N2O potential emissions compared to plant diversity in experimental plant communities.

Denitrification is an ecosystem process linked to ongoing climate change, because it releases nitrous oxide (N2O) into the atmosphere. To date, the literature covers mostly how aboveground (i.e. plant community structure) and belowground (i.e. plant-associated soil microbes) biota separately influence denitrification in isolation of each other. We here present a mesocosm experiment where we combine a manipulation of belowground biota (i.e. addition of Rhizophagus irregularis propagules to the indigenous mycorrhizal community) with a realized gradient in plant diversity. We used a seed mix containing plant species representative of mesophytic European grasslands and by stochastic differences in species establishment across the sixteen replicates per treatment level a spontaneously established gradient in plant diversity. We address mycorrhizal-induced and plant-diversity mediated changes on denitrification potential parameters and how these differ from the existing literature that studies them independently of each other. We show that unlike denitrification potential, N2O potential emissions do not change with mycorrhiza and depend instead on realized plant diversity. By linking mycorrhizal ecology to an N-cycling process, we present a comprehensive assessment of terrestrial denitrification dynamics when diverse plants co-occur.

Variance in biomass-allocation fractions is explained by distribution in European trees.

Intraspecific variability in ecological traits confers the ability of a species to adapt to an ever-changing environment. Fractions of biomass allocation in plants (BAFs) represent both ecological traits and direct expressions of investment strategies and so have important implications on plant fitness, particularly under current global change. We combined data on BAFs of trees in > 10 000 forest plots with their distributions in Europe. We aimed to test whether plant species with wider distributions have more or less variable intraspecific variance of the BAFs foliage-woody biomass and shoot-root ratios than species with limited distribution. Irrespective of corrections for tree age and phylogenetic relatedness, the standard deviation in BAFs was up to three times higher in species with the most extensive distributions than in those with the least extensive distribution due to a higher genetic diversity. Variance in BAFs also increased with latitude. We show that a combination of 36% tree genetic diversity and 64% environmental variability explains variance in BAFs and implies that changes in genetic diversity occur quickly. Genetic diversity should thus play a key role in regulating species responses to future climate change. Loss of habitat, even if transient, could induce a loss of genetic diversity and hinder species survival.