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ABSTRACT There is increasing evidence that microbial volatile organic compounds (mVOCs) play an important role in interactions between microbes in soils. In this minireview, we zoom in on the possible role of mVOCs in the suppression of plant-pathogenic soil fungi. In particular, we have screened the literature to see what the actual evidence is that mVOCs in soil atmospheres can contribute to pathogen suppression. Furthermore, we discuss biotic and abiotic factors that influence the production of suppressive mVOCs in soils. Since microbes producing mVOCs in soils are part of microbial communities, community ecological aspects such as diversity and assembly play an important role in the composition of produced mVOC blends. These aspects have not received much attention so far. In addition, the fluctuating abiotic conditions in soils, such as changing moisture contents, influence mVOC production and activity. The biotic and abiotic complexity of the soil environment hampers the extrapolation of the production and suppressing activity of mVOCs by microbial isolates on artificial growth media. Yet, several pathogen suppressive mVOCs produced by pure cultures do also occur in soil atmospheres. Therefore, an integration of lab and field studies on the production of mVOCs is needed to understand and predict the composition and dynamics of mVOCs in soil atmospheres. This knowledge, together with the knowledge of the chemistry and physical behaviour of mVOCs in soils, forms the basis for the development of sustainable management strategies to enhance the natural control of soil-borne pathogens with mVOCs. Possibilities for the mVOC-based control of soil-borne pathogens are discussed. The authors review literature reporting on pathogen suppressive activities of volatiles (mVOCs) produced in soils by microbial communities and indicate management strategies to enhance mVOC-mediated disease control.

Two patterns of bacterial growth response upon drying and rewetting (DRW) of soils have previously been identified. Bacterial growth can either start increasing immediately after rewetting in a linear fashion (“type 1” response) or start increasing exponentially after a lag period (“type 2” response). The effect of repeated DRW cycles was studied in three soils with different response patterns after a single DRW cycle (“type 1”, “type 2” with a short lag period and “type 2” with a long lag period). The soils were exposed to seven DRW cycles, and respiration and bacterial growth were monitored after 1, 2, 3, 5, and 7 cycles. Exposure to repeated DRW shifted the bacterial growth response from a “type 2” to a “type 1” pattern, resulting in an accelerated growth recovery to a pre-disturbance growth rate. Bacterial growth in soils that initially had a “type 1” response also tended to recover faster after each subsequent DRW cycle. The respiration patterns after DRW also indicated the same transition from a “type 2” to a “type 1” pattern. Our results show that exposure to repeated DRW cycles will shape the bacterial response to future DRW cycles, which might be mediated by a shift in species composition, a physiological adjustment, evolutionary changes, or a combination of the three.

Abstract Climate change alters frequencies and intensities of soil drying-rewetting and freezing-thawing cycles. These fluctuations affect soil water availability, a crucial driver of soil microbial activity. While these fluctuations are leaving imprints on soil microbiome structures, the question remains if the legacy of one type of weather fluctuation (e.g., drying-rewetting) affects the community response to the other (e.g., freezing-thawing). As both phenomenons give similar water availability fluctuations, we hypothesized that freezing-thawing and drying-rewetting cycles have similar effects on the soil microbiome. We tested this hypothesis by establishing targeted microcosm experiments. We created a legacy by exposing soil samples to a freezing-thawing or drying-rewetting cycle (phase 1), followed by an additional drying-rewetting or freezing-thawing cycle (phase 2). We measured soil respiration and analyzed soil microbiome structures. Across experiments, larger CO 2 pulses and changes in microbiome structures were observed after rewetting than thawing. Drying-rewetting legacy affected the microbiome and CO 2 emissions upon the following freezing-thawing cycle. Conversely, freezing-thawing legacy did not affect the microbial response to the drying-rewetting cycle. Our results suggest that drying-rewetting cycles have stronger effects on soil microbial communities and CO 2 production than freezing-thawing cycles and that this pattern is mediated by sustained changes in soil microbiome structures.

The physiological performance of organisms depends on their environmental context, resulting in performance–response curves along environmental gradients. Parasite performance–response curves are generally expected to be broader than those of their hosts due to shorter generation times and hence faster adaptation. However, certain environmental conditions may limit parasite performance more than that of the host, thereby providing an environmental refuge from disease. Thermal disease refuges have been extensively studied in response to climate warming, but other environmental factors may also provide environmental disease refuges which, in turn, respond to global change. Here, we (1) showcase laboratory and natural examples of refuges from parasites along various environmental gradients, and (2) provide hypotheses on how global environmental change may affect these refuges. We strive to synthesize knowledge on potential environmental disease refuges along different environmental gradients including salinity and nutrients, in both natural and food-production systems. Although scaling up from single host–parasite relationships along one environmental gradient to their interaction outcome in the full complexity of natural environments remains difficult, integrating host and parasite performance–response can serve to formulate testable hypotheses about the variability in parasitism outcomes and the occurrence of environmental disease refuges under current and future environmental conditions.

In recent years, microbiomes and their potential applications for human, animal or plant health, food production and environmental management came into the spotlight of major national and international policies and strategies. This has been accompanied by substantial R&D investments in both public and private sectors, with an increasing number of products entering the market. Despite widespread agreement on the potential of microbiomes and their uses across disciplines, stakeholders and countries, there is no consensus on what defines a microbiome application. This often results in non‐comprehensive communication or insufficient documentation making commercialisation and acceptance of the novel products challenging. To showcase the complexity of this issue we discuss two selected, well‐established applications and propose criteria defining a microbiome application and their conditions of use for clear communication, facilitating suitable regulatory frameworks and building trust among stakeholders. Advances in microbiome research have resulted in microbiome applications increasingly entering the market. Commercialisation of these novel applications is associated with challenges, often caused by non‐comprehensive communication or insufficient documentation. Criteria defining a microbiome application and their conditions of use for clear communication, facilitating suitable regulatory frameworks and building trust among stakeholders are presented.

Invasive exotic plant species effects on soil biota and processes in their new range can promote or counteract invasions via changed plant–soil feedback interactions to themselves or to native plant species. Recent meta-analyses reveale that soil influenced by native and exotic plant species is affecting growth and performance of natives more strongly than exotics. However, the question is how uniform these responses are across contrasting life forms. Here, we test the hypothesis that life form matters for effects on soil and plant–soil feedback. In a meta-analysis we show that exotics enhanced C cycling, numbers of meso-invertebrates and nematodes, while having variable effects on other soil biota and processes. Plant effects on soil biota and processes were not dependent on life form, but patterns in feedback effects of natives and exotics were dependent on life form. Native grasses and forbs caused changes in soil that subsequently negatively affected their biomass, whereas native trees caused changes in soil that subsequently positively affected their biomass. Most exotics had neutral feedback effects, although exotic forbs had positive feedback effects. Effects of exotics on natives differed among plant life forms. Native trees were inhibited in soils conditioned by exotics, whereas native grasses were positively influenced in soil conditioned by exotics. We conclude that plant life form matters when comparing plant–soil feedback effects both within and between natives and exotics. We propose that impact analyses of exotic plant species on the performance of native plant species can be improved by comparing responses within plant life form.

The overarching biological impact of microbiomes on their hosts, and more generally their environment, reflects the co-evolution of a mutualistic symbiosis, generating fitness for both. Knowledge of microbiomes, their systemic role, interactions, and impact grows exponentially. When a research field of importance for planetary health evolves so rapidly, it is essential to consider it from an ethical holistic perspective. However, to date, the topic of microbiome ethics has received relatively little attention considering its importance. Here, ethical analysis of microbiome research, innovation, use, and potential impact is structured around the four cornerstone principles of ethics: Do Good; Don’t Harm; Respect; Act Justly. This simple, but not simplistic approach allows ethical issues to be communicative and operational. The essence of the paper is captured in a set of eleven microbiome ethics recommendations, e.g., proposing gut microbiome status as common global heritage, similar to the internationally agreed status of major food crops.

In addition to challenges like climate change and biodiversity loss, the sustainability and resilience of agrifood systems worldwide are currently challenged by new threats, such as the COVID-19 pandemic and the Ukraine war. Furthermore, the resilience and sustainability of our agrifood systems need to be enhanced in ways that simultaneously increase agricultural production, decrease post-harvest food losses and food waste, protect the climate, environment and health, and preserve biodiversity. The precarious situation of agrifood systems is also illustrated by the fact that overall, around 3 billion people worldwide still do not have regular access to a healthy diet. This results in various forms of malnutrition, as well as increasing number of people suffering from overweight and obesity, and diet-related, non-communicable diseases (NCDs) around the world. Findings from microbiome research have shown that the human gut microbiome plays a key role in nutrition and diet-related diseases and thus human health. Furthermore, the microbiome of soils, plants, and animals play an equally important role in environmental health and agricultural production. Upcoming, microbiome-based solutions hold great potential for more resilient, sustainable, and productive agrifood systems and open avenues toward preventive health management. Microbiome-based solutions will also be key to make better use of natural resources and increase the resilience of agrifood systems to future emerging and already-known crises. To realize the promises of microbiome science and innovation, there is a need to invest in enhancing the role of microbiomes in agrifood systems in a holistic One Health approach and to accelerate knowledge translation and implementation.

Invasive exotic plant species are often expected to benefit exclusively from legacy effects of their litter inputs on soil processes and nutrient availability. However, there are relatively few experimental tests determining how litter of exotic plants affects their own growth conditions compared to congeneric native plant species. Here, we test how the legacy of litter from three exotic plant species affects their own performance in comparison to their congeneric natives that co-occur in the invaded habitat. We also analyzed litter effects on soil processes. In all three comparisons, soil with litter from exotic plant species had the highest respiration rates. In two out of the three exotic-native species comparisons, soil with litter from exotic plant species had higher inorganic nitrogen concentrations than their native congener, which was likely due to higher initial litter quality of the exotics. When litter from an exotic plant species had a positive effect on itself, it also had a positive effect on its native congener. We conclude that exotic plant species develop a legacy effect in soil from the invaded range through their litter inputs. This litter legacy effect results in altered soil processes that can promote both the exotic plant species and their native congener.

Climate change is expected to increase future abiotic stresses on ecosystems through extreme weather events leading to more extreme drought and rainfall incidences [Jentsch A, et al. (2007) Front Ecol Environ 5(7):365–374]. These fluctuations in precipitation may affect soil biota, soil processes [Evans ST, Wallenstein MD (2012) Biogeochemistry 109:101–116], and the proportion of exotics in invaded plant communities [Jiménez MA, et al. (2011) Ecol Lett 14:1277–1235]. However, little is known about legacy effects in soil on the performance of exotics and natives in invaded plant communities. Here we report that drought and rainfall effects on soil processes and biota affect the performance of exotics and natives in plant communities. We performed two mesocosm experiments. In the first experiment, soil without plants was exposed to drought and/or rainfall, which affected soil N availability. Then the initial soil moisture conditions were restored, and a mixed community of co-occurring natives and exotics was planted and exposed to drought during growth. A single stress before or during growth decreased the biomass of natives, but did not affect exotics. A second drought stress during plant growth resetted the exotic advantage, whereas native biomass was not further reduced. In the second experiment, soil inoculation revealed that drought and/or rainfall influenced soil biotic legacies, which promoted exotics but suppressed natives. Our results demonstrate that extreme weather events can cause legacy effects in soil biota, promoting exotics and suppressing natives in invaded plant communities, depending on the type, frequency, and timing of extreme events.