Soil organic matter (SOM) is well known to exert a great influence on physical, chemical, and biological soil properties, thus playing a very important role in agronomic production and environmental quality. Globally SOM represents the largest terrestrial organic C stock, which can have significant impacts on atmospheric CO2 concentrations and thus on climate. The changes in soil organic C content are the result of the balance of inputs and losses, which strongly depends on the processes of organic C stabilization and protection from decomposition in the soil. This session will provide a forum for discussion of recent studies on the stabilization and sequestration mechanisms of organic C in soils, covering any physical, chemical, and biological aspects related to the selective preservation and formation of recalcitrant organic compounds, occlusion by macro and microaggregation, and chemical interaction with soil mineral particles and metal ions.

Soil organic matter (SOM) plays a vital role not only in soil fertility and quality (by providing a number of physical, chemical, and biological benefits), but also in C cycling.
The decline of SOM represents one of the most serious threats facing many arable lands of the world. Crop residues and animal manures have long been used as soil organic amendments to preserve and enhance SOM pools. Nowadays, organic amendments originate from many kinds of organic wastes, which are being increasingly produced mainly by farms, food and energy industries, and municipalities. Besides serving as a source of organic matter and plant nutrients, these materials may contribute to fight plant diseases and reduce soil contamination, erosion, and desertification.
At the same time, a safe and useful application of organic amendments requires an in-depth scientific knowledge of their nature and impacts on the soil-plant system, as well as on the surrounding environment.
This session will focus on the current research and recent advances on the use of organic amendments in modern agriculture as well as for the restoration of degraded soils, covering physical, chemical, biological, biochemical, environmental and socio-economical aspects.

Soil organic matter (SOM) dynamics play a major role in determining soil fertility, atmospheric CO2 concentrations and climate change adaptation. However, the relationship between soil C persitance and vulnerability under increasing atmospheric temperature and growing global population is poorly understood. Therefore better constraints on SOM pools and fluxes and their reaction to global change are required allowing to disentangle soil C persistence and vulnerability. This session focuses on empirical and modeling studies of soil carbon and its response to warming, and ecosystem vulnerability in different soil types. Contributions focusing on organic as well as mineral soils in contrasting climatic regions are welcome. They may include interdisciplinary research from experiments and observation networks collecting long term, geographically distributed data. International efforts working towards soil data harmonization and data-model sharing are also featured.

Organo-mineral associations are recognized as key factors in stabilizing organic matter within microaggregates and even larger structural units in soil. A better understanding of the mechanisms behind the formation and stabilization are essential to predict or manage soil
structure, fertility and organic matter dynamics. Recent studies point to the highly dynamic nature
of the structural units of soil, while the major interaction mechanisms, e.g. adsorption and
and coprecipitation, are strongly dependent on the environmental conditions. Microaggregates including the OM-associations may form, alter, and break up depending on the local milieu (i.e., the presence of minerals, redox conditions, pH, water content, type of organic molecules, biotic drivers, etc.), under natural and management-induced variations in soil. With the growing experimental and observational evidence of the existence and build-up of these sub-micrometer soil compounds, in turn the number of modeling approaches increase that aim for an advanced mechanistic understanding of the formation and stabilization processes, the resulting 3d-structures, and their role in the functioning of soil. With this session, we respond to the growing awareness and intensive debate of the importance of the sub-micrometer-architecture for the dynamics and functioning of soils. Presentations will focus on studies that investigate organo-mineral interactions up to the size of microaggregates in soil and sediments, including their time dependence, conceptual, analogic or numerical modeling, the spatial explicit characterization of organo-mineral associations down to the nanoscale through high-resolution imaging microscopies and spectroscopies, the impact of plant C input, the role of the soil fauna and microorganisms, as well as their potential to increase C storage in any types of ecosystem.

Note: This session is a merger of SSS5.6 "Organo-mineral association dynamics in soil" and SSS5.10 "Microaggregates in Soil"

Fate and activity of heavy metals, pesticides, PAHs and other xenobiotics depend on their interaction with humic substances present in soil, coal, freshwater and marine systems. They may be deactivated due to various interactions with humic substances, and from the other hand, xenobiotics may affect the properties of humic substances. These processes are dependent on the properties of specific fractions, including humic acids, fulvic acids and humin. Papers covering various aspects of mutual interaction between humic substances and heavy metals, pesticides and PAHs are welcome. This will provide deeper insights and understanding of the mechanisms of xenobiotics sorption on humic substances, as well as their influence on properties of humic substances occurring in terrestrial and aquatic systems.

Soils represent a major terrestrial carbon store and fulfil a variety of functions from which the environment and humankind benefit. Soils processes operate and interact across the Critical Zone: the near-surface terrestrial layer extending from the bedrock through to the lower atmosphere. Multiple external pressures may result in changes to soil functioning, and we need a good understanding of how soils respond at a range of spatial and temporal scales.

The storage, stability, and cycling of carbon is fundamental to the resilience of soil systems. It is essential that we consider the role of carbon in all soil systems, from the microbial and aggregate scale to the catchment and the whole land surface, in order to better understand the interconnectivity between rocks, soils, plants, and the atmosphere. This is particularly important as soils are facing multiple perturbations, ranging from rapid shifts in land use and management to degradation and long-term environmental and climatic change. To maintain soil functions we need to develop further knowledge of how resistant soils are to these changes, alongside if, and how, they recover.

This session will consider terrestrial carbon pools and dynamics, and explore soil resilience at any, or multiple scales. We welcome contributions that consider processes within and between different elements of the Critical Zone, alongside innovative methods of quantifying and investigating change. Early career researchers are strongly encouraged to apply, and we seek submissions considering empirical, modelling, or meta-analytical approaches.

Organic substances in the soil are very heterogeneous and include low and high molecular weight compounds, and may be derived from plant and microbial residues. Besides contribution to soil organic matter (SOM) formation, living microorganisms regulate C and nutrient cycles by recycling processes. Detailed analyses of SOM transformation can highlight the role of selective preservation mechanisms, for example, and how these are modified and influenced by biological, physical and chemical interactions. In order to link processes of SOM formation with the pools, the broad range of approaches is used, including an application of various isotopes 13C/14C, 15N, 18O, 33P and analysis of plant and microbial biomarkers comprising both structural and chemical aspects related to SOM turnover. The specific attention is dedicated to the low molecular weight organic substances (LMWOS), which serve as a fuel for microorganisms, regulates their activity, composition, the transition from dormant to active stages and transformation of SOM (e.g. priming effect).
Thus, this session invites contributions, especially from early-career students, to i) the fate and turnover of organic substances in soil: from uptake and utilization by microorganisms to stabilization in SOM, ii) functions of LMWOS for priming of SOM decomposition, regulation of nutrient availability and rock weathering, iii) microbial recycling of elements (C, N, and P) from fresh or aged organic material. Analytical approaches comprising structural and chemical aspects related to SOM, such as potential biomarkers, isotopes, and their combinations are highly desirable. We also encourage contributors to present and discuss analytical challenges that remain due to both environmental and analytical uncertainty.

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