Soil structure is essential for soil biota and soil functioning. But its study remains difficult because of its heterogeneity in space and time. To understand the interactions between soil structure and soil biodiversity, a strong interdisciplinary approach merging soil physics, soil ecology and soil chemistry is needed. Soil structure defines the myriad of microhabitats that host the unparalleled biodiversity observed in soils. The micro-gradients in oxygen, moisture, nutrients and organic compounds act as ecological filters for soil biota and define soil functioning. The soil structure is also highly variable in time, being constantly re-modelled by numerous factors such as the alternation of wet and dry cycles, the activity of the soil biota, especially plant roots and ecosystem engineers (e.g. microbes, notably filamentous fungi stabilizing aggregates, soil macrofauna, etc.), and the input of fresh organic matter.
In this session, we invite interdisciplinary contributions on: (i) the formation and spatiotemporal variability of the soil structure, and on (ii) the role of the soil microhabitat in determining soil biodiversity. Field, experimental and modeling approaches are welcome. The ultimate aim is to understand how soil structure, from micro-architecture to macropores, emerges from interactions within soil, and how it determines the outcome of soil processes (e.g mineralization) that have an important outreach for plants (e.g through mycorrhizae for example).

Soil is the habitat for a myriad of organisms. These include soil fauna who are crucial in providing soil related ecosystem services, often through their interaction with microorganisms and plants. Soil fauna encompass a wide diversity of organisms including protozoa, nematodes, enchytraeids, microarthropods, as well as large invertebrates (e.g., earthworms, beetles). Variation in soil properties and climate result in a heterogeneous distribution of soil fauna across the globe. Soil fauna substantially affect litter decomposition and soil organic matter formation, and are key agents in soil structure formation. Their activity can result in the production of decomposition by-products which are still poorly chemically and physically characterized, despite the fact that they are a springboard for soil organic matter formation as well as a potential source of nutrients. Soil fauna therefore have a central role in soil biogeochemical cycling.

In this session, we welcome contributions on a wide range of topics related to the effect of soil fauna on biogeochemical cycling (e.g., organic carbon storage, nutrient availability, gas emissions) in interaction with soil properties (e.g., aggregation, bioturbation, biopores, weathering). We call for studies on the effect of soil fauna on litter decomposition and the analyses of the decomposition by-products, as well as studies that tackle the interactions between soil fauna, plants and microorganisms. We are especially interested in studies that provide mechanistic (rather than stochastic) links between faunal activity and ecosystem services. Studies can cover various scales (from microscale to landscape) and approaches using physical fractionation, molecular methods (e.g., amino sugars, lipids, PLFAs, DNA), and imaging (e.g., SEM, TEM, nanoSIMS, µCT), spectroscopic and/or isotopic techniques. We also encourage contributions investigating the changing role of soil fauna under climate change, land use changes and land cover change.

Soil organisms comprise a large fraction of global terrestrial diversity and are responsible for essential ecosystem functions and services, such as determining plant productivity, nutrient cycling, organic matter decomposition, pollutant degradation and pathogen control. However, soil biodiversity and its functional roles are determined by the abiotic surrounding. As such, anthropogenic influences including urbanization, land-use change, pollution, invasions etc., alter soil biodiversity and its functions. Here we aim to showcase recent advances on how anthropogenic drivers determine soil biodiversity and how that subsequently feeds-back to ecosystem functions and human health.
This session invites contributions that showcase examples of: 1) Mapping soil biodiversity under different anthropogenic influences; 2) Understanding the functional implication of anthropogenic changes of soil biodiversity; 3) Protecting and restoring biodiversity in anthropogenically altered soils; 4) Manipulating soil biodiversity to increase ecosystem functions and human health under anthropogenic factors.

Anthropogenic greenhouse-gas emissions are drastically shaping global climate, increasing temperatures and contributing to more frequent extreme weather events. Terrestrial ecosystem responses to climate change can induce a large feedback via the control of biogeochemical cycles, for instance by regulating carbon fluxes that are 10 times larger than human emissions. A large portion of carbon and nutrient cycling is controlled by soil processes, in which microorganisms play a central role. Soil microbial communities and their physiological traits are, in turn, influenced by both gradual climate changes and more extreme short-term weather events. Thus, understanding the impacts of climate on soil microbial communities and microbe-mediated processes is critical for improving predictions of the resistance and resilience of terrestrial ecosystems in the future.

This session aims to elucidate the impacts of different climate scenarios on soil microbial communities and biogeochemical cycling, and their feedback to climate change. We will focus on different aspects of climate change, ranging from gradual changes such as increasing atmospheric CO2 or temperature, to the effects of more extreme weather events such as heatwaves, drying-rewetting cycles or floods. We invite studies on the resilience and associated recovery dynamics of soil biota to the mentioned environmental disturbances, as well as on their resistance or adaptation mechanisms. Studies with a focus on links between microbial community composition and function, as well as interactions between soil microorganisms, plants and fauna, are particularly welcomed. We aim to connect researchers from different disciplines and to create a discussion platform to review the current state-of-the-art, identify knowledge gaps, share ideas, and tackle new challenges in the field.

Microbial hotspots in soils such as the rhizosphere, detritusphere, biopores, hyphasphere, aggregate surfaces, pore space and etc, are characterized by high activity and fast process rates resulting in accelerated turnover of soil organic matter and other microbial functions (e.g. nutrient mobilization, litter decomposition, respiration, organic matter stabilization, greenhouse gas emission, acidification, etc.). The intensity of microbial and SOM turnover as well as nutrient cycling in such hotspots is at least one order of magnitude higher than in the bulk soil.
This session invites contribution to: 1) Various aspects of microbial activity, interactions, communities composition and distribution in hotspots; 2) Factors influencing (micro)biological nutrient (re)cycling including biotic and abiotic controls (e.g. climatic extreme, warming, drought, etc) are strongly encouraged; 3) The session will also present and discuss new developments to assess the crucial microbial mechanisms that underpin biogeochemical processes in hotspots (e.g. approaches assessing the variability in soil activity within the soil matrix, notably focusing on microbial molecular analysis and imaging methods); 4) Combination of experimental and theoretical approaches to predict the fate and functions of microorganisms in hotspots are highly appreciated.

The rhizosphere is regarded as the soil compartment with the highest level of nutrient flux through a multitude of interactions between plants, soil, and (micro)biota. Roots and associated (micro)organisms interact with heterogeneous soil environments that provide habitats for biota on various scales. High metabolic activity and nutrient cycling can be observed from single root tips to whole root systems which makes the rhizosphere of central importance for ecosystem functioning.
The main knowledge-gaps in rhizosphere research are related to the difficulty in mechanistically linking the physical, chemical and biological processes, taking place at different scales (nm to cm) in the rhizosphere and to the challenge of upscaling these processes to the scale of the root system and the soil profile. The key for overcoming these knowledge gaps is to understand rates of matter flux, and to link the spatial arrangement of the different interconnected components of the rhizosphere with their temporal dynamics. This requires concerted efforts to combine methods from different disciplines like plant genomics, imaging, soil physics, chemistry and microbiology.
We welcome experimental and modelling studies on rhizosphere functioning that aim at revealing spatial gradients of e.g. functional biodiversity of microorganisms, uptake and release patterns by roots, soil structure modification by root growth (and vice versa) as well as feedbacks between those processes in order to improve our mechanistic understanding of emerging properties like water acquisition, nutrient cycling, plant health, soil structure development and feedbacks among them.