Most studies exploring the relation between the quality of organic substrates and microbial activity have been carried out with individual substrates. However, they have largely overlooked potential effects that might occur when microorganisms simultaneously process a heterogeneous mixture of organic substances. We investigated whether the degree of molecular richness of substrate mixtures had an impact on the overall activity of microbial communities, measured as heat dissipation over a day, in a laboratory incubation experiment. Topsoil samples were taken from a Swedish long-term field trial, established in 1983, in which a crop rotation dominated by spring cereals was either under-sown with perennial ryegrass as a cover crop or was without cover crops. No significant differences in the cumulative heat dissipation between soil with or without cover crops were observed. When all substrate mixtures were evaluated, the substrate richness was not significantly correlated with the overall microbial activity. However, we observed a bell-shaped curve between the total microbial activity and the nominal oxidation state of carbon (C) in the substrate mixtures. In most cases, the measured heat dissipated from soils that received substrate mixtures was significantly higher than the theoretically expected heat dissipation. The latter was based on the weighted sum of heat dissipated of individual substrates. This pattern was more visible in soil without cover crops than in soil with cover crops. The higher-than-expected heat dissipation from substrate mixtures suggests that the response of soil microbial communities to diverse substrates is not simply additive. There are several possible explanations for the observations made: (i) interactions among microbial metabolic pathways, (ii) added substrates may be preferentially used, and (iii) concentration of all the substrates in the mixtures was lower than when added individually, and therefore the metabolic pathways for each substrate was less likely to be saturated. Chemodiversity, the diversity of organic chemical compounds, is often not considered in models evaluating the dynamics of soil organic matter. Our results warrant further investigations into microbial metabolism and the processing of heterogeneous organic substances in order to constrain microbial- and substrate-specific models of soil organic matter.

The R3-0020 agricultural long-term field experiments investigate the effect of nitrogen addition levels and straw removal on crop yield and soil properties. The field experiments are located at the Swedish University of Agricultural Sciences (SLU) four field research stations: L & ouml;nnstorp (Lund), Lanna (Skara), S & auml;by (Uppsala) and R & ouml;b & auml;cksdalen (Ume & aring;). The field site in S & auml;by has been maintained since 1970 and the three other sites since 1980. The experiments consist of a cereal only crop rotation, a crop residue treatment (straw removed or incorporated to the soil) and four nitrogen fertilization levels (0, 50, 100 and 150 kg N ha(-1) yr(-1)). Aboveground crop biomass has been collected annually since the beginning of the experiments (Fig. 1), while topsoil samples were collected 2-8 times in the first 10-20 years and every four year since the 90 s (Fig. 2). We report crop yields and nutrient content for grain and straw, as well as carbon and macronutrient content for soils. The data presented here provides a useful time series for investigating the impacts of cereal-only crop rotation, straw removal and nitrogen fertilization levels on soil organic carbon and yield. (c) 2026 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

The R3-0020 agricultural long-term field experiments investigate the effect of nitrogen addition levels and straw removal on crop yield and soil properties. The field experiments are located at the Swedish University of Agricultural Sciences (SLU) four field research stations: Lönnstorp (Lund), Lanna (Skara), Säby (Uppsala) and Röbäcksdalen (Umeå). The field site in Säby has been maintained since 1970 and the three other sites since 1980. The experiments consist of a cereal only crop rotation, a crop residue treatment (straw removed or incorporated to the soil) and four nitrogen fertilization levels (0, 50, 100 and 150 kg N ha-1 yr-1). Aboveground crop biomass has been collected annually since the beginning of the experiments (Fig. 1), while topsoil samples were collected 2-8 times in the first 10-20 years and every four year since the 90s (Fig. 2). We report crop yields and nutrient content for grain and straw, as well as carbon and macronutrient content for soils. The data presented here provides a useful time series for investigating the impacts of cereal-only crop rotation, straw removal and nitrogen fertilization levels on soil organic carbon and yield.

Mineral fertilizers containing phosphorus (P) are widely used in agriculture to enhance soil fertility, yet their impact on soil microbial communities remains unclear. Most studies rely on a single-site approach and observe short-term effects, limiting our ability to extricate long-term P impacts from other drivers of microbial communities. This study aimed to explore the influence of long-term P fertilization on soil microbial communities along the depth gradient across four countries, including grasslands and arable sites. Microbiomes were strongly affected by location, land management, and soil depth. No changes in the composition of prokaryotic communities were detected in response to P fertilization, while fungal communities demonstrated a modest response, but only at 0-10 cm depth in grassland soil. The almost complete absence of P fertilization impacts on communities could be due to a lack of changes in soil properties and nutrient availability after P fertilization. This is likely because of the applied P rate being below the threshold needed to alter soil properties or as a consequence of a legacy from previous P fertilization events. The strongest effect of P fertilization was observed at 0-10 cm depth, where carbon (C) and nitrogen (N) availability was higher. Together, these findings suggest that soil microbial communities are largely resistant to long-term P fertilization, with responses strongly mediated by sitespecific conditions. Our study highlights the importance of considering multiple long-term sites, land use types, and soil depths in research focused on P fertilization effects on soil microbial communities.

ABSTRACT The effects of long‐term phosphorus (P) fertilisation in agroecosystems on nitrogen (N) cycling are still elusive, in terms of P‐induced increase or reduction of N availability for plants and microorganisms, thereby affecting plant growth and also N 2 O emissions. Therefore, we performed detailed 15 N tracing analyses in soils from three different European long‐term P fertilisation experiments (LTE) in the laboratory and compared high‐P application treatments to the corresponding non‐P‐fertilised controls. In addition, carbon (C) fluxes (CO 2 , CH 4 ) were examined. The soils were sourced from Johnstown Castle, Ireland (JC, grassland), Jyndevad, Denmark (JY, arable soil), and Lanna Skara, Sweden (LS, arable soil) and were treated with two different combinations of 15 N‐labelled NH 4 NO 3 and 13 C‐labelled dried maize leaves ( 15 NH 4 NO 3 + 13 C; NH 4 15 NO 3 + 13 C). Gross N transformation rates were quantified by using the Ntrace Gas analysis tool. We found more pronounced effects of long‐term P fertilisation on N and C transformations in soils from the annually P‐fertilised LTEs (JC and JY) than in soils fertilised with P every 6 years (LS). In all soils, N immobilisation exceeded N mineralisation. The annually P‐fertilised soils showed increased mineralisation and immobilisation turnover, and across all LTEs, P fertilisation led to slightly elevated nitrification rates. Autotrophic and heterotrophic nitrification pathways varied among the LTEs. P fertilisation did not alter N 2 O emissions, but raised CO 2 emissions in all LTEs. Only the annually P‐fertilised soils showed higher microbial biomass C concentration and CH 4 uptake. These results highlight the importance of comparative studies to obtain an integrative perspective of long‐term P fertilisation affecting N and C transformations in soils.

Plant roots are essential for water and nutrient acquisition and constitute a major source of organic matter input to soil, underscoring their significance in global change adaptation and mitigation. Thereby, the partitioning of carbon between biomass formation and respiration in growing roots plays a decisive role for root foraging efficiency and carbon retention in the plant-soil system. Here, we elucidated structural-functional relationships between root growth physiology and root anatomy in rice (Oryza sativa L.) to uncover the hitherto unknown mechanisms regulating root carbon partitioning in response to warming. High-resolution X-ray computed tomography (1.8 μm) revealed nonlinear temperature responses in cortical cell volume of primary roots, which peaked at ∼28 °C and decreased at lower and higher temperatures. Similar nonlinearities occurred for root carbon partitioning during the first 4 d of growth following primary root emergence. At low and high temperatures, carbon allocation shifted from root biomass formation toward respiration. Compared with an ABA biosynthesis mutant (Osaba2-1), the wild type showed >40% greater temperature sensitivity in both cortical cell volume and carbon partitioning. Genotypic dose-response curves and structural-functional relationships between root cortical cell volume and carbon partitioning (R2 = 0.50) provided evidence that the ability to maintain cortical cell expansion under temperature stress increases carbon allocation to biomass formation over respiration. Thus, our study highlights the pivotal importance of fundamental root physiological processes in shaping the impacts of global warming on carbon fluxes in plant-soil systems that underpin plant growth, productivity, and terrestrial carbon cycling.

National soil monitoring programs and the EU-level Land Use/Land Cover Area Frame Survey (LUCAS) operate in parallel, repeatedly taking soil samples and analyzing them to support policies on monitoring soil health, including soil organic carbon (SOC). However, the comparability of SOC changes derived from different monitoring programs remains uncertain. In this study, we aimed to identify the sources of these differences and to illustrate the effect of land cover classification on SOC change. The LUCAS soil sampling did not reflect the actual proportions of cropland and grassland in Sweden. Overlaying the LUCAS grassland points with the Swedish Land Parcel Identification System (LPIS) showed that about 65% of the extracted points belonged to arable rotations, and 76% of this inconsistency was attributed to leys and fallow. We further compared SOC changes in the topsoil of cropland and grassland using LUCAS data from 2009, 2015, and 2018, before and after adjusting land cover using LPIS. The median change in SOC between 2015 and 2018 was 0.11% (95% CI -0.01%-0.17%, effect size 0.22) for continuous cropland (CC), and 0.22% (95% CI -0.11%-0.54%, effect size 0.25) for continuous grassland (GG). After adjustment, SOC change became significant and more positive for CC (median 0.15%, 95% CI 0.09%-0.25%, effect size 0.35), but less positive for GG (median 0.08%, 95% CI -0.81-0.70, effect size 0.01). Further differentiating ley occurrence in the arable rotation and grassland subgroups showed a larger SOC increase with higher ley occurrence in arable rotations, but a less positive or even negative SOC change in grassland subgroups. The trends in SOC changes after adjusting land cover became similar to those observed in the Swedish national inventories. Our results highlight the importance of recognizing differences among cropping systems and the need for improving data harmonization across monitoring programs.

Simulation models are potentially useful tools to test our understanding of the processes involved in the turnover of soil organic carbon (SOC) and to evaluate the role of management practices in maintaining stocks of SOC. We describe here a simple model of SOC turnover at the soil profile scale that accounts for two key processes determining SOC persistence (i.e. microbial energy limitation and physical protection due to soil aggregation). We tested the model and evaluated the identifiability of key parameters using topsoil SOC contents measured in three treatments with contrasting organic matter inputs (i.e. fallow, mineral fertilized and cropped, with and without straw addition) in a long-term field trial. The estimated total input of organic matter (OM) in the treatment with straw added was roughly three times that of the treatment without straw addition, but only 12 % of the additional OM input remained in the soil after 54 years. By taking microbial energy limitation and enhanced physical protection of root residues into account, the model could explain the differences in C persistence among the three treatments, whilst also accurately matching the time-courses of SOC contents using the same set of model parameters. Models that do not explicitly consider microbial energy limitation and physical protection would need to adjust their parameter values (either decomposition rate constants or the retention coefficient) to match this data. We also performed a sensitivity analysis to identify the most influential parameters in the model determining soil profile stocks of OM at steady-state. Input distributions for soil and crop parameters in the model were defined for the agricultural production region in east-central Sweden that includes Uppsala. This analysis showed that model parameters affecting SOC decomposition rates, including the rate constant for microbial-processed SOC and the parameters regulating physical protection and microbial energy limitation, are more sensitive than parameters determining OM inputs. The development of pedotransfer approaches to estimate SOC decomposition rates from soil properties would therefore support predictive applications of the model at larger spatial scales.

Implementing sustainable soil management practices to enhance soil health is a priority in research and policymaking across Europe. There is a need to identify the main soil challenges faced by different European stakeholders and the critical threats limiting the adoption of sustainable management of agricultural soils. The present study analyses stakeholders' perspectives on key soil challenges, knowledge gaps, and priorities for agricultural soil research across partner countries that participated in the European Joint Programme on Soil (EJP SOIL) 2020-2025. Two complementary stakeholder activities-a survey and a workshop-were conducted across 24 partner countries (divided into four regions: Central, Northern, Southern, and Western Europe) of the EJP SOIL consortium in 2024. Among 10 pre-identified soil challenges, the findings highlight that maintaining or increasing soil organic carbon, avoiding soil sealing, and avoiding soil erosion are the top three priorities across Europe. However, the perceived prioritisation of soil challenges differed both between and within regions, reflecting each country's specific soil health context. Divergences in perceptions between practitioners and other stakeholder groups underscore the need to develop actions aimed at better understanding the rationale behind such discrepancies and how to overcome them. In addition, other key challenges for achieving sustainable soil management across Europe include limited funding, policy incoherencies, poor knowledge dissemination and co-creation, and insufficient soil monitoring. Environmental factors influencing soil health, including climate change, together with governance and economic models, were perceived to be critical limitations to the adoption of sustainable management of agricultural soils. This study also emphasises the need for a diversity of engagement methods, policies, and system approaches to support a transition towards sustainable soil management. These findings underscore the need for future research agendas that focus on integrated knowledge and participatory approaches, and strategies involving societal awareness and policy alignment-key elements that have also informed broader strategies involving societal awareness and engagement towards sustainable soil management in Europe.

Soil temperatures are expected to increase with climate change, which will likely affect soil bioturbation by earthworms. While the ecophysiological response of earthworms to soil temperature has been studied previously, several questions remain, such as whether earthworm species from different geographical origins respond differently to environmental stress. In this study, we used A. caliginosa individuals from two contrasting European climatic zones (i.e. central Sweden and southern France), and measured their energy use (via heat dissipation using isothermal calorimetry) and their burrowing activity (i.e. burrow volume and cast volume, quantified using X-ray imaging) at five different soil temperatures (i.e. 8, 12, 16, 20 and 24 °C).In general, heat dissipation in earthworms increased with soil temperature, and body mass-normalized heat dissipation was about 20% higher in earthworms from France. Moreover, the increase in heat dissipation with increasing temperature was stronger at high than at low temperatures. However, there was one important exception from these general trends: earthworms from Sweden showed a distinct and absolute peak in heat dissipation at intermediate temperature (16 °C). Burrow volumes created by earthworms increased with soil temperature up to 16-20 °C, after which it decreased. The high levels of heat dissipation in combination with reduced burrowing activity at 24 °C suggest high stress in such warm conditions. The volumes of burrows created by Swedish earthworms were about 50% higher than those created by French earthworms.As a consequence of the higher heat dissipation and lower burrow volumes, the specific energy costs for burrowing (i.e., heat dissipation per unit burrow volume) was 2-3-fold higher in French earthworms than Swedish earthworms, which suggests that Swedish earthworms are more “efficient”. In general, French A. caliginosa were smaller in size and mass compared to Swedish A. caliginosa, and these differences may be a result of adaptation to distinct climates. While Swedish earthworms had a distinct activity peak at 16 °C, we could not find such an activity peak in French earthworms. Measurements with higher temperature resolution (e.g., measurements every 1 °C) might be needed.Our data indicate that the geographical origin of earthworms plays a role in the earthworm's ecophysiological responses to environmental stressors such as soil temperature. The findings provide quantitative data on how earthworm burrowing activity is affected by soil temperature, which helps us better understand how earthworms may adapt to climate change and what the consequences on soil processes are.

The ease of hulling an oat genotype and the length of time the intact and hulled seeds can be stored viably without deteriorating quality has always been of interest to industry and farmers. We evaluated the hulling traits of different genotypes under varying growing conditions in 2018 and 2020, linking this to seed morphological and physiological features. We found that inhullability, seed viability and formed oxidized products varied among the genotypes as well as the environmental conditions. The oat cultivars (Symphony, Kyron, and Delfin) presented higher hullability in 2020, whereas Fatima and Morrison from the same year, all of the tested genotypes from 2018, and the later seeds sown in 2020 presented higher inhullability. Two sets of seeds representing high and low hullability were further analyzed to test the hypothesis that hullability is associated with seed health using isothermal calorimetry, morphological observations, and volatile fingerprinting. Seed quality, in terms of viability, decreased in seeds with higher inhullability and in seeds stored without hulls when compared to seeds with hulls. Seed viability is associated with kernel hullability, while the accumulated total volatiles, hexanal, pentanal, and pentadecane contents are associated with higher inhullability and lower seed viability.

Managing agroecosystems to enhance soil organic carbon (SOC) storage is important for mitigating climate change. However, the transformation of SOC is intimately connected to nutrient cycling, particularly nitrogen (N) and phosphorus (P). While P constraints on plant growth are known, their effects on carbon (C) and N cycling remain uncertain. The study uses several long-term experiments (LTEs) to determine the importance of N-P interactions and the optimal C:N:P stoichiometry for long-term SOC stocks in managed agricultural systems. The aim was to determine the influence of multi-decadal P fertilisation on SOC stocks and stoichiometric interactions of C, N and P in agricultural soils (up to 50 cm) across different soil textural classes and land uses. For this, the soils were sampled at three depths 0-10, 10-30 and 30-50 cm from six LTEs in Europe (three grasslands and three arables) to determine soil physico-chemical properties. The results showed comparable SOC stocks in contrasting P treatments across land uses. In grasslands, SOC stocks at 0-50 cm depth ranged from 9.7 to 40.6 t C ha(-1) while in arable sites, they were between 11.0 and 48.3 t C ha(-1). The SOC stocks did not vary significantly across P treatments indicating that long-term P fertilisation did not affect C storage. Grassland sites had higher SOC stocks in the 0-10 cm, while at arable sites they were higher at 10-30 cm depths. The maximum predicted SOC stock of 30.9 t C ha(-1) was with SOC/TN (total nitrogen) ratio of 10.1 and SOC/TP (total phosphorus) ratio of 32.6 in grassland sites, while these ratios were 10.9 and 29.4, respectively, in arable sites, where the predicted maximum SOC stock was 33.3 t C ha(-1). Overall, the study shows that the long-term phosphorus fertilisation of grassland and arable soils did not affect SOC stocks at the studied LTEs.

Soil structure is a key feature in controlling the turnover of organic matter in soils. The spatial arrangement of solids and pores in agricultural topsoil can be actively influenced by management practices, such as tillage and cropping systems, which in turn can affect the resident microbial communities and their activities. However, carbon mineralisation and microbial activity are usually measured in sieved samples, which provides information on gross potentials under optimal conditions. Under these conditions, the spatial heterogeneities that are specific to different management practices are reduced or totally removed. In this study, we combined X-ray computer tomography (X-ray CT) and isothermal calorimetry to investigate the effect of soil structure on heat dissipation, as an indicator of biological activity. Samples were collected from the topsoil of a long-term field experiment (12 years) that included four different land uses: conventional vs. reduced tillage, each with either maize or winter wheat as the main crop in the rotation. We compared the response of undisturbed soil cores (3 cm in height, 2.7 cm in diameter) to the addition of water and glucose in specific pore sizes, ranging in radii of 15 to 75 mu m or 3 to 75 mu m. The pore structure and indicators of particulate organic material were quantified using Xray CT with a voxel resolution of 15 mu m. This allowed us to distinguish between the effects of crop rotation and tillage regime on biological activity, soil structure and the feedback between the two. Heat dissipation correlated significantly with X-ray CT derived porosity, pore surface density and soil matrix grey value, all of which were affected by both tillage regime and crop rotation. Heat dissipation in maize plots after glucose addition to the pore size range with radii of 3 to 75 mu m was greater than in the winter wheat systems, but not when added to the pore size range with radii of 15 to 75 mu m. The study showed that structural indicators can explain up to 81 % and 95 % of the variance in total heat dissipation after glucose and water addition, respectively, but only 60 % of the heat dynamics, here defined as the time taken for 50 % of total heat to be dissipated. The results emphasise the importance of soil structure in regulating microbial decomposition of soil organic matter and warrants further investigations.

Sequestering atmospheric CO2 within soil organic matter via shifts in agricultural practices represents a compelling strategy for enhancing soil ecosystem services and mitigating global change. Traditionally, the perception of soil carbon (C) stability is focused on intrinsic characteristics of organic matter inputs, such as lignin content. However, recent studies challenge this perspective, proposing a more effective approach centered on managing how the soil microbiome processes C inputs (Sokol et al., 2019; Poeplau et al., 2019). This shift prompts an exploration into the intricate connection between aboveground plant communities and belowground diversity of the microbiome, as well as the associated metabolic processes governing C sequestration. Building on this, Lehmann et al. (2020) presented a theoretical framework that interprets the persistence of C in soil as a consequence of interactions between the molecular variability of organic matter input and the spatio-temporal microbial heterogeneities within the soil system. This perspective underscores the need for a comprehensive understanding of the dynamic interplay shaping C sequestration, moving beyond static views of organic matter stability. Therefore, within the EnergyLink framework various microbial markers were investigated to shed light on potential physiological changes at a microbial level across several European agricultural field sites with different cover crop management types. Specifically, to discern shifts in microbial necromass composition and quantity, we focused on amino sugars (galactosamin, gluctosamine, mannosamine and muramic acid). To evaluate effects on potential growth rates, we quantified 14C incorporation into ergosterol for fungi and 14C-leucine incorporation for bacteria. Comprehending changes in uptake strategies, we examined extracellular enzyme activities for different nutrient classes. Additionally, we determined C:N:P ratio for bulk soil and microbial biomass. Here we present first results and discuss implications of diversified cover crops on soil carbon properties.

Microbial transformation of soil organic matter plays a critical role in carbon (C) cycling making it essential to understand how land use and management practices influence microbial physiology and its connection to C dynamics. One factor that is likely to impact soil microbial physiology is crop diversification via its influence on belowground diversity (e.g., chemical heterogeneity of C inputs, microbial community composition). However, the effect of crop diversification measures on microbial physiology and potential effects on C cycling in agricultural soils is still unclear. To address this knowledge gap, we sampled topsoil from eight experimental sites covering different crop diversification measures across Europe (i.e., cover crops, ley farming, vegetation stripes). We used the 18O-labelling method to analyse microbial C use efficiency (CUE), growth, respiration and biomass C. Additionally, a second sampling at five selected sites examined whether the growing season influenced the impact of crop diversification. Meta-analysis revealed no overall effect of crop diversification on CUE, microbial activity, biomass or soil organic C (SOC). However, the effects varied with the type of diversification measure: cover crops did not affect carbon processing, vegetation stripes increased microbial activity, and ley farming enhanced CUE. The largest variation in CUE was observed between samplings at the same sites, indicating seasonal dynamics. Temperature, precipitation and photosynthetically active radiation predicted seasonal variation in CUE (R-2 = 0.36). While cover crops did not significantly impact C storage in our study, both ley farming and vegetation stripes increased SOC. The overall effect of crop diversification on SOC seems to be decoupled from highly temporally variable CUE in the bulk soil and rather relate to C-inputs.

Microbial carbon-use efficiency (CUE) in soils captures carbon (C) partitioning between anabolic biosynthesis of microbial metabolites and catabolic C emissions (i.e. respiratory C waste). The use of C for biosynthesis provides a potential for the accumulation of microbial metabolic residues in soil. Recognised as a crucial control in C cycling, microbial CUE is implemented in the majority of soil C models. Due to the models' high sensitivity to CUE, reliable soil C projections demand accurate CUE quantifications. Current measurements of CUE neglect microbial non-growth metabolites, such as extracellular polymeric substances (EPS) or exoenzymes, although they remain in soil and could be quantitatively important. Here, we highlight that disregarding non-growth anabolism can lead to severe underestimations of CUE. Based on two case studies, we demonstrate that neglecting exoenzyme and EPS production underestimates CUE by more than 100% and up to 30%, respectively. By incorporating these case-specific values in model simulations, we observed that the model projects up to 34% larger SOC stocks over a period of 64 years when non-growth metabolites are considered for estimating CUE, highlighting the crucial importance of accurate CUE quantification. Our considerations outlined here challenge the current ways how CUE is measured and we suggest improvements concerning the quantification of non-growth metabolites. Research efforts should focus on (i) advancing CUE estimations by capturing the multitude of microbial C uses, (ii) improving techniques to quantify non-growth metabolic products in soil, and (iii) providing an understanding of dynamic metabolic C uses under different environmental conditions and over time. In the light of current discussion on soil C stabilisation mechanisms, we call for efforts to open the ‘black box’ of microbial physiology in soil and to incorporate all quantitative important C uses in CUE measurements.

Soil functioning contributes to the delivery of a vast range of ecosystem goods and services, and ecosystem health is therefore reflected by the capacity of the soil to perform underlying functions. Soil organic carbon (SOC) is a key indicator for soil quality as it is an integral driver of many soil functions and associated ecosystem services. Across the globe, SOC stocks are declining due to expanding agriculture and unsustainable practices. Awareness of the fact that soil is a non-renewable resource and its functioning important for all life on Earth is increasing, especially among policymakers. As such, goals for the preservation and restoration of SOC are formulated in policies under the European Green Deal. However, the evaluation of these goals at the European level is hampered by a non-harmonized diversity in national SOC monitoring strategies. While some SOC indicators can be useful for the evaluation of most policy goals (i.e., baseline and potential SOC stocks), additional and contrasting SOC data are often required for the evaluation of the goals formulated by the different EU directives. This study provides an overview of five ongoing SOC monitoring programmes across Europe and discusses how national programmes may be aligned to evaluate goals at the EU level. Five countries with very different soil monitoring programmes were included in a case study to illustrate the potential for harmonization and standardization of SOC assessment. Based on this study, we conclude that SOC monitoring strategies can be harmonized, but not standardized. We further suggest five sampling strategies that have potential for harmonization under the proposed Directive on Soil Monitoring and Resilience.

Earthworm burrowing is essential for soil functioning in temperate climates. It is known that soil compaction hampers earthworm burrowing, but there is a lack of knowledge on how it affects the energy costs of earthworms. In the present study, we used respirometry and isothermal calorimetry to quantify earthworm respiration rates and heat dissipation in two endogeic species, Aporrectodea caliginosa and Aporrectodea tuberculata, in compacted and non-compacted soils. We put the measured respiration rates and heat dissipation in relation to the burrow volume and cast volume produced by the earthworms. We found that at higher compaction levels, respiration rates and dissipated heat increased for both studied species. The energy costs associated with burrowing were a significant fraction of the total energy costs. Our results indicate that energy costs per burrow volume increase due to compaction, and that the specific energy costs for burrowing (i.e., per gram earthworm) were lower for A. tuberculata than for A. caliginosa. Further studies are needed to confirm our results. We discuss the potential and current limitations of isothermal calorimetry as a method for direct quantification of energy costs of earthworms. There is a need for further studies that quantify how energy costs of burrowing are affected by various soil conditions, to better predict the implications of land use and soil management on soil processes and functions mediated by earthworm burrowing.

Most studies of the relationships between the composition of soil organic matter and plant cover have been carried out at the plant genera level. However, they have largely overlooked the potential effects that plant varieties, belonging to the same genus, can have on soil organic matter. We investigated whether plant varieties belonging to different Salix species (S. dasyclados and S. viminalis) impacted the composition of organic matter using mid-infrared spectroscopy and pyrolysis GC/MS. Top-soils were taken from an 18 year-old long-term field trial where six Salix varieties were grown as short-rotation coppice under two fertilisation regimes. Significant differences in the molecular composition and diversity of the soil organic matter were observed in the fertilised plots. The effects were mostly visible at the species level, i.e. the organic matter in soil under S. dasyclados varieties had higher molecular diversity and lignin content than under S. viminalis, potentially due to differences in the amount and composition of their litter inputs. Smaller differences among varieties from the same species were also observed. No significant effects of Salix varieties were observed in the unfertilised plots. The relatively high degree of spatial variability of several soil properties found in these plots may have masked plant variety and/or species effects. This study provides evidence that the identity of Salix species or varieties can affect the molecular composition and diversity of soil organic matter. The corresponding traits should be considered in breeding programmes to enhance soil organic C accumulation and persistence.

Soil structure is a key feature in controlling microbial access to organic matter in soils. The spatial arrangement of solids and pores in agricultural soils is shaped by the used tillage and crop system. However, spatial heterogeneities make it difficult to determine relationships between soil biology and soil structure, and often homogenized, sieved soils are used to evaluate organic matter turnover in soils. In this study, we used heat dissipation as an indicator for biological activity in soils taken from two different tillage systems (conventional vs. reduced tillage) and two different cropping systems (crop rotations with either maize or winter wheat as main crop) running for 12 years. In order to evaluate the impact of soil structure, we investigated the response of both repacked and undisturbed soil cores (3 cm in height, 2.7 cm in diameter) to water and glucose addition. Pore structure indicators and particulate organic matter content were quantified by X-ray computer tomography at a resolution of 15 µm.We will show that calorimetry is a suitable tool to monitor the biodegradation of C sources in undisturbed soil cores and that both tillage system and crop rotation effect biological activity in soil. In summary, soil under maize cultivation dissipated more heat compared to the wheat crop rotation. In both, repacked and undisturbed samples, conventional tillage promoted heat dissipation in response to water addition, likely due to the annual incorporation of labile organic matter. However, structural and organic matter indicators could only explain the variance in heat dissipation to some extent. Thus, the usage of undisturbed soil cores provides new challenges to evaluate the link between soil structure and microbial activity due to increased variability.