Formation of mineral-associated organic matter (MAOM) is a key process in the global carbon cycle, stabilising organic carbon in soils. The relative importance of mineral composition and land use as potential controls of MAOM stability at regional scales and underlying microbial processes are still unresolved. Here, we assessed the stability of MAOM formed on goethite (iron oxide) and illite (phyllosilicate clay) exposed for five years in topsoils at 68 forest and grassland sites across Germany. We incubated the newly formed MAOM, determined its extractability, and analysed the composition and functioning of associated microbial communities. Decomposition of MAOM was always significantly lower for goethite than illite, highlighting that higher organic carbon accumulation on goethite was not exclusively due to its larger sorption capacity. Instead, reduced organic carbon extractability and higher phosphorus-acquiring enzyme activities indicated stronger substrate limitation of microbial growth on goethite than illite. Across the two minerals, MAOM decomposition was consistently lower for forests than grasslands, relating to greater nutrient constraints and a different microbial community composition in forests. Overall, mineral type and land use explained 34.6 and 23.2% of the variance in MAOM decomposition. The pronounced land use effect on MAOM stability underlines its potential responsiveness to environmental change.

Mineral surfaces in soil, where fungal communities contribute to the formation and turnover of mineral-associated OM (MAOM), are important interfaces for organic matter (OM) and nutrient cycling. The significance and contribution of secondary minerals such as goethite (iron oxide) or illite (clay mineral) to fungal community structure and functioning under natural conditions in forest soils remains elusive. We placed mineral containers filled with mixtures of secondary minerals (either goethite or illite) and quartz-sand in 30 forest topsoils across three regions in Germany for five years. The mineral samples in the containers were separated from the surrounding soil with 50-mu m mesh barriers. Mineral and surrounding soil samples were analyzed for abundance and community composition of saprotrophic and ectomycorrhizal fungi based on phospholipid fatty acid profiles and amplicon sequencing, and for enzyme activities (beta-glucosidase, beta-xylosidase, N-acetylglucosaminidase, and acid phosphatase). Compared to the surrounding soil, fungal communities in the carbon-poor mineral samples were less diverse and communities were distinct. The community composition of saprotrophic fungi was affected by mineral type, likely reflecting variability in the minerals' capacities to bind OM. Higher relative microbial enzymatic nutrient acquisition was associated with a shift from saprotrophic towards ectomycorrhizal fungi, indicating a tight link between trophic fungal groups and their distinct functional roles in the mineralosphere. At a larger scale, we observed strong site effects, suggesting that environmental filters such as physico-chemical soil properties, tree species, and region shape the structuring of fungal communities more strongly than the specific mineralosphere conditions.

Organismal functional strategies form a continuum from slow- to fast-growing organisms, in response to common drivers such as resource availability and disturbance. However, whether there is synchronisation of these strategies at the entire community level is unclear. Here, we combine trait data for >2800 above- and belowground taxa from 14 trophic guilds spanning a disturbance and resource availability gradient in German grasslands. The results indicate that most guilds consistently respond to these drivers through both direct and trophically mediated effects, resulting in a ‘slow-fast’ axis at the level of the entire community. Using 15 indicators of carbon and nutrient fluxes, biomass production and decomposition, we also show that fast trait communities are associated with faster rates of ecosystem functioning. These findings demonstrate that ‘slow’ and ‘fast’ strategies can be manifested at the level of whole communities, opening new avenues of ecosystem-level functional classification.

Litterfall is an important pathway by which organic carbon in forest ecosystems is transferred from plants to soil. The amount and chemical composition of litterfall, the rate of litter decomposition and the extent of litter incorporation into the soil are relevant for the formation of the organic layer and soil organic matter. However, the interaction between forest management, litterfall, organic layer formation and mineral soil carbon stocks has rarely been considered together. Since 2015, we have been monitoring the above-ground litter input with a total of 750 litter traps in 150 forests in 3 German regions (Schorfheide-Chorin, Hainich-Dün and Swabian Alb). In 2017, 2021 and 2023, the organic layer and the topsoil (0-10 cm) were sampled at 14 sampling points per plot. The silvicultural management intensity index (SMI) introduced by Schall and Ammer (2013) was used to quantify forest management intensity at all plots. Piecewise structural equation modeling (SEM) showed that C stocks in the organic layer were positively related to the proportion of conifers and negatively related to timber harvesting. There was also a negative relationship between C stocks in the organic layer and mineral soil pH. These relationships were mediated by litter C input, litter CN ratio and earthworm biomass. While C stocks in the organic soil layer were positively related to litter C input and litter CN ratio, we found a negative relationship with earthworm biomass. In our model, these effects explained 46 % of the variance in carbon stocks in the organic layer. In addition, the study region explained a further 18% of the variance. A comparison of the relative importance of the different factors influencing carbon storage in the organic layer showed that tree species and litter CN ratio were by far the most strongly associated with carbon stocks in the soil organic layer. The effects of timber harvest and soil pH, mediated by litter C mass and earthworm biomass, were significant but comparatively weak. A direct influence of pH on the carbon stock of the organic soil layer could not be detected. In contrast to the organic layer, we found no direct or indirect influence of forest management intensity on mineral soil OC stocks in 0-10 cm. While litter C mass and litter CN ratio were not related to OC stocks in the mineral soil, we found a very strong positive correlation between clay content, soil pH and OC stocks in the mineral soil (p<0.001). We also found a weak correlation between dithionite extractable iron and mineral soil OC stocks (p<0.05). All three factors together explained 67% of the variance in mineral soil OC stocks (0-10 cm), and the study regions explained a further 11% of the variance. Our results show that forest management and especially tree species selection are strongly reflected in the organic layer. However, the regional gradient of forest management was not large enough to be visible in the mineral soil, where carbon stocks are mainly determined by parent material and associated clay and iron oxide contents.

Mineral surfaces in soil are an important interface for organic matter (OM) and nutrient cycling, with associated microorganisms contributing to the formation and turnover of mineral-associated OM (MAOM). However, the relevance of intrinsic (mineral type) versus extrinsic (land-use intensity) factors on the co-development of MAOM and microorganisms under natural conditions remains poorly understood. Mineral containers filled with mixtures of quartz-sand and pristine secondary minerals (goethite or illite) were exposed to 50 grassland topsoils of the Schwäbische Alb (Germany) along a land-use intensity gradient for five years. Mineral samples and soils were analyzed for organic carbon (OC) and nutrients (N and P), abundance and composition of major microbial groups based on phospholipid fatty acid profiles, as well as enzyme activities (β-glucosidase, β-xylosidase, N-acetylglucosaminidase, and acid phosphatase). Microorganisms colonized both mineral samples to the same extent, with goethite samples exhibiting greater MAOM accumulation and higher enzyme activities than illite samples. Both mineral samples differed from the overlying soils with greater relative abundances of fungi and Gram-negative bacteria and greater microbial acquisition of nutrients (N and P) relative to C as indicated by the stoichiometry of enzyme activities. Increasing land-use intensity was associated with decreasing C:N ratios and microbial abundances for goethite samples and increasing β-glucosidase activity for illite samples while the proportion of fungi was reduced in both mineral samples. We conclude that in the studied temperate grasslands the association of OM and microorganisms with secondary minerals is driven more by mineral type and reactivity than by differences in land-use intensity. The different minerals apparently formed distinct microhabitats with unique characteristics that differed in MAOM accumulation and microbial access to OC and nutrients, thus affecting microbial colonization and functionality.

Across the tree of life, organismal functional strategies form a continuum from slow-to fast-growing organisms, in response to common drivers such as resource availability and disturbance. However, the synchronization of these strategies at the entire community level is untested. We combine trait data for >2800 above-and belowground taxa from 14 trophic guilds spanning a disturbance and resource availability gradient in German grasslands. Most guilds consistently respond to these drivers through both direct and trophically-mediated effects, resulting in a ‘slow-fast’ axis at the level of the entire community. Fast trait communities were also associated with faster rates of whole ecosystem functioning. These findings demonstrate that ‘slow’ and ‘fast’ strategies can be manifested at the level of whole ecosystems, opening new avenues of ecosystem-level functional classification.

A key to forest productivity is structure and function of the biotic microbiome in the soil, which determines nutrient mineralisation and consequently tree growth and fitness. Soil nematodes are a dominant part of these assemblages, with an important role in the associated micro-food web. However, nothing is known about how forest management and soil properties affect soil nematodes. This study investigated the nematode communities in the organic layer and mineral soil of 150 forests located in three different German regions. Fifty forest stands each were studied in Schwabische Alb (ALB), Hainch-Diin (HAI) and Schorfheide-Chorin (SCH). The effect of forest management (forest management index - ForMI, silvicultural management intensity indicator - SMI), soil properties (total C, N, S, P, organic C, inorganic C, pH, water content) and microbial food source (phospholipid fatty acids - PLFA) on nematode density, community and ecological indices were assessed. The nematode density in the organic layer of the forests was with a mean of 290 individuals g(-1)DW comparable across all three regions, while in the mineral soil nematode density was significant lower in SCH. Here, dry sandy soils are frequently stocked with intensively managed pine forests, and the associated fungal-based decomposition is reflected in a greater proportion of fungal-feeding nematodes and a higher Channel Index. Effects of region and soil layer were mirrored by the structure of the nematode community. Organic layer and mineral soil differed distinctly, while in the latter SCH separated from ALB and HAI. The nematode community was predominantly affected by region, soil properties and resources, with microbial diet as driving factor in the organic layer, whereas soil parameters were more important in mineral soil. In comparison, the influence of forest management was low, with ForMI and SIM together explaining 8% (organic layer) and 4% (mineral soil) of the overall variation. Most remarkable, the nematode community in HAI, a region dominated by broad-leaf forests, was resilient to management intensity in the organic layer. On the other hand, management practice had family-specific impact: In the organic layer of ALB, the density of the bacterial-feeding Teratocephalidae and the fungal-feeding Aphelenchoididae increased with higher Inonat (indicates non-natural tree species) and higher SMIr (addresses stand age and species selection related to the risk of stand loss). In sum, the structure and function of nematode communities were driven by both, biotic factors such food source (i.e. the soil layer inhabited) and abiotic factors such as soil type and climate (i.e. region). Furthermore, forest management can affect nematode communities, mainly by the selected tree species, but also by stand age and density.

Purpose Simultaneous effects of more than one global change driver on ecosystem functioning have rarely been assessed. Methods We disentangled the effects of region encompassing climatic and edaphic conditions, forest-management intensity and community plant diversity on litterfall quantity, quality and turnover in 27 temperate forests across an environmental gradient. Results Region significantly influenced litterfall and organic layer mass and chemical quality and litter and element turnover. After accounting for the influence of region, increasing forest-management intensity (ForMI) significantly decreased litterfall mass, N, P and K concentrations and nutrient fluxes and slowed down litter and nutrient turnover. Because increasing ForMI reflected the man-made contributions of coniferous trees, these results can partly be attributed to the lower litterfall at our study sites and slower litter turnover of coniferous than deciduous trees. After accounting for the influences of region and ForMI, increasing diversity of the vascular plant community on the study plots measured as species richness or Shannon index significantly increased C and decreased N, P and S concentrations in litterfall. Together with the significantly decreased N and P concentrations in the organic layer with increasing plant diversity, these results indicated an increased within-stand nutrient-use efficiency and a more complete soil nutrient use with increasing plant diversity. Conclusions Our results demonstrate that increasing ForMI, which is associated with increasing conifer shares, leaves element stocks in the organic layer unchanged but slows down C turnover and thus increases temporary C storage in soil organic layers. Moreover, community vascular plant diversity helps close nutrient cycles.

Plants have evolved complex physiological mechanisms to regulate production of defense secondary metabolites (SMs) to cope with environmental stress such as drought. Yet, these mechanisms remain under-studied in mature trees, limiting our ability to understand effects of climate change on tree productivity and survival. We investigated defense SMs and their relations to growth, nonstructural carbohydrates and phytohormones across seasons, in a Mediterranean forest dominated by two tree species with different resistance to drought. Our results showed seasonality of leaf SMs, with a strong accumulation of SMs during cold and dry conditions in winter. The drought-resistant species Phillyrea latifolia had high levels of SMs in both leaves (ca. 10–20%) and stem phloem (4–6%), but experimental drought decreased SMs and soluble sugars in stem phloem in spring and summer. By contrast, the drought-susceptible species Quercus ilex had relatively low and constant levels of SMs, irrespective of drought. We further showed that P. latifolia leaves had generally higher levels of jasmonic acid and lower salicylic acid than Q. ilex leaves, potentially leading to differences in SMs and growth between the two co-occucrring species. Our study suggests that species- and organ-specific dynamics of defense SMs are driven by phytohormones and carbohydrates in mature trees, and that P. latifolia may become less resistant to abiotic and biotic stress due to reduced phloem defense SMs and carbohydrates in a drying climate.

Soil respiration is rarely studied at the landscape scale where forest and soil properties can be important drivers. We performed forest and soil inventories in 150 temperate forest sites in three German landscapes and measured in situ soil CO2 efflux with the soda-lime method in early summer 2018 and 2019. Both years were affected by naturally occurring summer droughts. Our aim was to investigate the impact of forest structural and compositional properties, soil properties and climate on soil CO2 efflux at the landscape. Forest properties explained a large portion of soil CO2 efflux variance (i.e., 14% in 2018 and 20% in 2019), which was comparable or larger than the portion explained by soil properties (i.e., 15% in 2018 and 6% in 2019), and much larger than that of climate. Using Structural Equation Modeling, we found that forest structural properties, i.e., tree density and basal area, were negatively linked to soil CO2 efflux, while forest composition, i.e., conifer share and tree species richness, was not important. Forest structure effects on soil CO2 efflux were either direct or mediated by fine root biomass under dry summer conditions. Summer soil CO2 efflux was positively linked to fine root biomass but not related to total soil organic carbon stocks or climate. Forest structural properties influence soil CO2 efflux under drought events and should be considered when predicting soil respiration at the landscape scale.

&lt;p&gt;Forest ecosystems in central Europe are currently experiencing various environmental changes like ongoing nitrogen deposition, rising CO&lt;sub&gt;2&lt;/sub&gt; levels and more frequent summer droughts, with potential impacts on biogeochemical processes in soils. Monitoring of soil properties, especially sensitive indicators like the activities of extracellular enzymes, enables studying the net effect of different simultaneously ongoing global changes on soil processes. Therefore, we measured the potential activities of four extracellular enzymes related to the C, N, P and S cycle (beta-glucosidase, N-actetyl-glucosaminidase, acid phosphatase and sulfatase)&amp;#160; of topsoils (0-10 cm of the mineral soil) from 150 forest plots under different management in three German regions as part of the Biodiversity Exploratories (https://www.biodiversity-exploratories.de/en/) project (Swabian Alb in the South, Hainich-D&amp;#252;n in the center and Schorfheide Chorin in the North of Germany) in May of 2011, 2014, 2017 and 2021. Analyzed soil samples were mixed samples composed of 14 soil cores (5 cm diameter) per plot, taken along two 40 m transects, sieved to &lt; 2mm, and stored frozen before analyses. &amp;#160;Additional information on soil C, N and pH was obtained for the same samples. &lt;br /&gt;Results revealed that the interannual variation of enzyme activities was about twice as high as that of soil organic carbon contents. Organic carbon, total nitrogen contents or soil pH showed no consistent trend over time across the regions. The same was true for the enzymes beta-glucosidase, N-acetyl-glucosaminidase and sulfates while acid phosphatase activity increased in all regions from 2011 to 2021 with the smallest absolute increase from on average 1290 to 2753 nmol MUF g&lt;sup&gt;&amp;#8722;1&lt;/sup&gt; dw h&lt;sup&gt;&amp;#8722;1&lt;/sup&gt; in the sandy and most acidic region Schorfheide Chorin, and the largest one in the loess-dominated silt-clay soils of the Hainich-D&amp;#252;n region (from 3474 to 5570 nmol MUF g&lt;sup&gt;&amp;#8722;1&lt;/sup&gt; dw h&lt;sup&gt;&amp;#8722;1&lt;/sup&gt;).&amp;#160; Accordingly, the ratio of carbon-to-phosphorus acquiring enzymes declined with time. Plots following Moorhead et al. (2016, http://dx.doi.org/10.1016/j.soilbio.2015.10.01) indicated a consistent shift from N- to P-limitation across regions, independent of their total P contents and for both, coniferous and deciduous forests. Forest ecosystems seem to need to acquire more P from organic sources but given that both, plants and microorganisms can produce acid phosphatase, we are currently not able to say, if the increased phosphatase activity was a direct plant response or one (potentially mediated) by microorganisms. However, elevated CO&lt;sub&gt;2&lt;/sub&gt; and N-deposition can both potentially lead to nutrient imbalances and thus increasing forest P requirements, and also summer droughts might reduce plant nutrient uptake, so that the observed trend might be an additive effect of all, rather than being attributable to one alone. As next steps we will test if changes in enzyme activities go along with changes in soil microbial communities and with leaf litter P contents.&lt;/p&gt;

Formation of mineral-associated organic matter (MAOM) supports accumulation and stabilization of carbon in soil, and thus, is a key factor in the global carbon cycle. Little is known about the interplay of mineral type, land use, and management intensity on the extent of MAOM formation. We addressed this research question by exposing mineral containers with pristine minerals (goethite, as a representative of oxide-type mineral phases, and illite, representing layered aluminosilicate minerals) for five years to ambient soil conditions at 5 cm depth in 150 grassland and 150 forest plots in three regions across Germany. After recovery, the content of organic carbon (OC) of the minerals was determined by dry combustion. Results show that irrespective of land use and management intensity, more OC accumulated on goethite than illite (on average 0.23 and 0.06 mg m-2 mineral surface, respectively), demonstrating that mineral type was the most crucial factor for MAOM formation. Carbon accumulation was consistently greater in coniferous forests than in deciduous forests and grasslands. Structural equation models revealed that in grasslands, fertilization had contradictory effects on carbon accumulation, with the positive effect being mediated by enhanced plant productivity and the negative effect by reduced plant species richness. Overall, our results suggest that OC stabilization in soil is primarily driven by mineral type, in particular iron and other metal oxides. The mineral-driven MAOM formation is further modified by land use and management intensity.

Formation of mineral-associated organic matter (MAOM) supports the accumulation and stabilization of carbon (C) in soil, and thus, is a key factor in the global C cycle. Little is known about the interplay of mineral type, land use and management intensity in MAOM formation, especially on subdecadal time scales. We exposed mineral containers with goethite or illite, the most abundant iron oxide and phyllosilicate clay in temperate soils, for 5 years in topsoils of 150 forest and 150 grassland sites in three regions across Germany. Results show that irrespective of land use and management intensity, more C accumulated on goethite than illite (on average 0.23 ± 0.10 and 0.06 ± 0.03 mg m-2 mineral surface respectively). Carbon accumulation across regions was consistently higher in coniferous forests than in deciduous forests and grasslands. Structural equation models further showed that thinning and harvesting reduced MAOM formation in forests. Formation of MAOM in grasslands was not affected by grazing. Fertilization had opposite effects on MAOM formation, with the positive effect being mediated by enhanced plant productivity and the negative effect by reduced plant species richness. This highlights the caveat of applying fertilizers as a strategy to increase soil C stocks in temperate grasslands. Overall, we demonstrate that the rate and amount of MAOM formation in soil is primarily driven by mineral type, and can be modulated by land use and management intensity even on subdecadal time scales. Our results suggest that temperate soils dominated by oxides have a higher capacity to accumulate and store C than those dominated by phyllosilicate clays, even under circumneutral pH conditions. Therefore, adopting land use and management practices that increase C inputs into oxide-rich soils that are under their capacity to store C may offer great potential to enhance near-term soil C sequestration.

Soil respiration is an important pathway of soil organic carbon losses in temperate grasslands; however, it is rarely studied across broad management intensity gradients in a landscape. Using the soda-lime method, we measured in-situ soil CO 2 efflux with single measurements of long exposure time (i.e. 3 day long) in 150 grasslands in three German regions in early summer 2018 and 2019. The grasslands ranged from unfertilized and grazed grasslands to intensively fertilized and frequently harvested ones. To assess effects of grazing and fertilization intensities and plant diversity on soil CO 2 efflux, we used Structural Equation Modeling to account for direct effects and indirect effects through soil and plant organic matter quantity and quality. Soil CO 2 efflux was suppressed by limited water availability caused by naturally occurring droughts in both study years. Under the prevailing environmental conditions, grazing intensity, plant biomass and plant C:N ratio were not related to soil CO 2 efflux. In contrast, fertilization intensity was positively associated with soil CO 2 efflux (standardized coefficient of net effect: + 0.04 in 2018 and + 0.03 in 2019). This was because fertilization led to lower plant species richness and, thus, to lower C:N ratios in soils, which were associated with higher soil CO 2 efflux (plant species richness net effect: −0.09 in 2018 and −0.18 in 2019; soil C:N ratio direct effect: −0.23 in 2018 and −0.33 in 2019). Intensively managed grasslands have higher soil respiration than extensively managed, plant species-rich grasslands even under the extreme conditions of natural droughts.

Grassland management intensity influences nutrient cycling both directly, by changing nutrient inputs and outputs from the ecosystem, and indirectly, by altering the nutrient content, and the diversity and functional composition of plant and microbial communities. However, the relative importance of these direct and indirect processes for the leaching of multiple nutrients is poorly studied. We measured the annual leaching of nitrate, ammonium, phosphate and sulphate at a depth of 10 cm in 150 temperate managed grasslands using a resin method. Using Structural Equation Modeling, we distinguished between various direct and indirect effects of management intensity (i.e. grazing and fertilization) on nutrient leaching. We found that management intensity was positively associated with nitrate, ammonium and phosphate leaching risk both directly (i.e. via increased nutrient inputs) and indirectly, by changing the stoichiometry of soils, plants and microbes. In contrast, sulphate leaching risk was negatively associated with management intensity, presumably due to increased outputs with mowing and grazing. In addition, management intensification shifted plant communities towards an exploitative functional composition (characterized by high tissue turnover rates) and, thus, further promoted the leaching risk of inorganic nitrogen. Plant species richness was associated with lower inorganic nitrogen leaching risk, but most of its effects were mediated by stoichiometry and plant community functional traits. Maintaining and restoring diverse plant communities may therefore mitigate the increased leaching risk that management intensity imposes upon grasslands.

Acidobacteria occur in a large variety of ecosystems worldwide and are particularly abundant and highly diverse in soils. In spite of their diversity, only few species have been characterized to date which makes Acidobacteria one of the most poorly understood phyla among the domain Bacteria. We used a culture-independent niche modeling approach to elucidate ecological adaptations and their evolution for 4,154 operational taxonomic units (OTUs) of Acidobacteria across 150 different, comprehensively characterized grassland soils in Germany. Using the relative abundances of their 16S rRNA gene transcripts, the responses of active OTUs along gradients of 41 environmental variables were modeled using hierarchical logistic regression (HOF), which allowed to determine values for optimum activity for each variable (niche optima). By linking 16S rRNA transcripts to the phylogeny of full 16S rRNA gene sequences, we could trace the evolution of the different ecological adaptations during the diversification of Acidobacteria. This approach revealed a pronounced ecological diversification even among acidobacterial sister clades. Although the evolution of habitat adaptation was mainly cladogenic, it was disrupted by recurrent events of convergent evolution that resulted in frequent habitat switching within individual clades. Our findings indicate that the high diversity of soil acidobacterial communities is largely sustained by differential habitat adaptation even at the level of closely related species. A comparison of niche optima of individual OTUs with the phenotypic properties of their cultivated representatives showed that our niche modeling approach (1) correctly predicts those physiological properties that have been determined for cultivated species of Acidobacteria but (2) also provides ample information on ecological adaptations that cannot be inferred from standard taxonomic descriptions of bacterial isolates. These novel information on specific adaptations of not-yet-cultivated Acidobacteria can therefore guide future cultivation trials and likely will increase their cultivation success.

The impact of local biodiversity loss on ecosystem functioning is well established, but the role of larger-scale biodiversity dynamics in the delivery of ecosystem services remains poorly understood. Here we address this gap using a comprehensive dataset describing the supply of 16 cultural, regulating and provisioning ecosystem services in 150 European agricultural grassland plots, and detailed multi-scale data on land use and plant diversity. After controlling for land-use and abiotic factors, we show that both plot-level and surrounding plant diversity play an important role in the supply of cultural and aboveground regulating ecosystem services. In contrast, provisioning and belowground regulating ecosystem services are more strongly driven by field-level management and abiotic factors. Structural equation models revealed that surrounding plant diversity promotes ecosystem services both directly, probably by fostering the spill-over of ecosystem service providers from surrounding areas, and indirectly, by maintaining plot-level diversity. By influencing the ecosystem services that local stakeholders prioritized, biodiversity at different scales was also shown to positively influence a wide range of stakeholder groups. These results provide a comprehensive picture of which ecosystem services rely most strongly on biodiversity, and the respective scales of biodiversity that drive these services. This key information is required for the upscaling of biodiversity-ecosystem service relationships, and the informed management of biodiversity within agricultural landscapes.

The dynamics of soil carbon in grassland are partly determined by soil organic matter (SOM) composition. However, it remains unclear which role grassland management plays in the interplay between SOM composition and carbon dynamics. Using pyrolysis-field ionization mass spectrometry (Py-FIMS), we studied the effect of meadow, mown pasture and pasture on the molecular SOM composition in German topsoils. In sandy soils of the Schorfheide-Chorin region, SOM composition and stability were strongly affected by clay contents and concentrations of crystalline Fe-oxides. Here, the grassland management type influenced lipid proportions, which accounted for a maximum of 11.1% of the total ion intensity (TII) under mown pasture. In the Hainich-Dun region, SOM composition was mainly related to the SOM decomposition stage (abundance of potentially recalcitrant compounds) but not to minerals. Compound classes of carbohydrates (4.3% TII), phenols and lignin monomers (8.5% TII), N-containing compounds (2.2% TII) and peptides (4.6% TII) were highest under meadow, while compound classes of lignin dimers (3.4% TII) and lipids (8.1% TII) were highest under pasture. In the Schwabische Alb region, the proportion of free fatty acids (1.6 to 2.3% TII) was positively related to the C/N ratio (r = 0.86); SOM stability was positively affected by poorly crystalline Fe-oxide content (r = 0.85). The results suggest that grassland management is affecting SOM composition and stability and thus influence SOM dynamics in grasslands. However, the proportion and composition (Fe-oxide content) of the soil clay fraction overrode grassland management effects if soil clay/OC ratios were <10.

Understanding whether land use intensification causes regime shifts is of key importance for management, particularly if these shifts are associated with thresholds separating different ecosystem states and with hysteretic dynamics. Here we use a unique, long-term grassland database to identify thresholds in the response of 16 ecosystem functions and the diversities of 21 taxa to land use intensity. We show that aboveground diversity (5 of 10 taxa), shoot biomass and soil N retention showed threshold responses to land use intensity, i.e., abrupt changes between extensively and intensively managed grasslands. Time-series analysis revealed that ecosystem functions showed hysteresis around the threshold, while diversity did not. Shifting back to the functioning seen in extensively managed grasslands may therefore require larger reductions in land use intensity than shifting to the high intensity state. Identifying such thresholds along land use gradients is critical to prevent ecosystem degradation and conserve biodiversity and ecosystem functions.

Members of the verrucomicrobial clade 'Candidatus Udaeobacter' rank among the most dominant bacterial phylotypes in soil. Nevertheless, despite this global prevalence, in-depth analyses with respect to pH preferences of 'Ca. Udaeobacter' representatives are still lacking. Here, we utilized a recently designed primer pair, specifically targeting 'Ca. Udaeobacter', to investigate links between soil pH and the abundance as well as phylotype composition of this largely unexplored verrucomicrobial clade. Based on 150 forest and 150 grassland soils, comprising a broad pH range, we determined the highest total abundance of 'Ca. Udaeobacter' in strongly acidic soil (pH, ~5.1) and, noteworthy, in ultra-acidic soil (pH < 3.5) and at a pH ≥ 7, its abundance drastically declined. When we analysed the six most dominant amplicon sequence variants affiliated with 'Ca. Udaeobacter' separately, their abundances peaked within a pH range of approximately 4.7-5.2, and only in one case at slightly acidic soil pH (pH, 6.1). Our study benefits from a combination of quantitative real-time PCR and high-throughput amplicon sequencing, enabling for the first time a highly specific abundance analysis of representatives affiliated with 'Ca. Udaeobacter', which revealed that this globally abundant verrucomicrobial clade shows preferences for acidic soil.