Formation of mineral-associated organic matter in temperate soils is primarily controlled by mineral type and 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.

Land-use intensity alters networks between biodiversity, ecosystem functions, and services.

Land-use intensification can increase provisioning ecosystem services, such as food and timber production, but it also drives changes in ecosystem functioning and biodiversity loss, which may ultimately compromise human wellbeing. To understand how changes in land-use intensity affect the relationships between biodiversity, ecosystem functions, and services, we built networks from correlations between the species richness of 16 trophic groups, 10 ecosystem functions, and 15 ecosystem services. We evaluated how the properties of these networks varied across land-use intensity gradients for 150 forests and 150 grasslands. Land-use intensity significantly affected network structure in both habitats. Changes in connectance were larger in forests, while changes in modularity and evenness were more evident in grasslands. Our results show that increasing land-use intensity leads to more homogeneous networks with less integration within modules in both habitats, driven by the belowground compartment in grasslands, while forest responses to land management were more complex. Land-use intensity strongly altered hub identity and module composition in both habitats, showing that the positive correlations of provisioning services with biodiversity and ecosystem functions found at low land-use intensity levels, decline at higher intensity levels. Our approach provides a comprehensive view of the relationships between multiple components of biodiversity, ecosystem functions, and ecosystem services and how they respond to land use. This can be used to identify overall changes in the ecosystem, to derive mechanistic hypotheses, and it can be readily applied to further global change drivers.

Natural soils in OECD 222 testing - influence of soil water and soil properties on earthworm reproduction toxicity of carbendazim.

Soil sorption properties can influence the bioavailability of substances and consequently the toxicity for soil organisms. Current standardised laboratory testing for the exposure assessment of pesticides to soil organisms uses OECD artificial soil that does not reflect the high variation in chemical-physical soil properties found in natural agroecosystems. According to guideline OECD 222, earthworm reproduction tests with Eisenia fetida and the pesticide carbendazim were performed in four natural soils and OECD artificial soil. By using pF 1.6, which ensures a uniformity in actual soil water availability, the control reproduction performance of E. fetida in all natural soils was at the same level as OECD artificial soil. In a principle component analysis, the variation in toxicity between the tested soils was attributable to a combination of two soil properties, namely total organic carbon content (TOC) and pH. The largest difference of 4.9-fold was found between the typical agricultural Luvisol with 1.03% TOC and pH 6.2 (EC10: 0.17 (0.12-0.21) mg a.i. kg-1 sdw, EC50: 0.36 (0.31-0.40) mg a.i. kg-1 sdw) and OECD artificial soil with 4.11% TOC and pH 5.6 (EC10: 0.84 (0.72-0.92) mg a.i. kg-1 sdw, EC50: 1.07 (0.99-1.15) mg a.i. kg-1 sdw). The use of typical agricultural soils in standardised laboratory earthworm testing was successfully established with using the measure pF for soil moisture adjustment. It provides a more application-oriented approach and could serve as a new tool to refine the environmental risk assessment at lower tier testing or in an intermediate tier based approach.

Microbial drivers of plant richness and productivity in a grassland restoration experiment along a gradient of land-use intensity.

Plant-soil feedbacks (PSFs) underlying grassland plant richness and productivity are typically coupled with nutrient availability; however, we lack understanding of how restoration measures to increase plant diversity might affect PSFs. We examined the roles of sward disturbance, seed addition and land-use intensity (LUI) on PSFs. We conducted a disturbance and seed addition experiment in 10 grasslands along a LUI gradient and characterized plant biomass and richness, soil microbial biomass, community composition and enzyme activities. Greater plant biomass at high LUI was related to a decrease in the fungal to bacterial ratios, indicating highly productive grasslands to be dominated by bacteria. Lower enzyme activity per microbial biomass at high plant species richness indicated a slower carbon (C) cycling. The relative abundance of fungal saprotrophs decreased, while pathogens increased with LUI and disturbance. Both fungal guilds were negatively associated with plant richness, indicating the mechanisms underlying PSFs depended on LUI. We show that LUI and disturbance affect fungal functional composition, which may feedback on plant species richness by impeding the establishment of pathogen-sensitive species. Therefore, we highlight the need to integrate LUI including its effects on PSFs when planning for practices that aim to optimize plant diversity and productivity.

Carbohydrate depletion in roots impedes phosphorus nutrition in young forest trees.

Nutrient imbalances cause the deterioration of tree health in European forests, but the underlying physiological mechanisms are unknown. Here, we investigated the consequences of decreasing root carbohydrate reserves for phosphorus (P) mobilisation and uptake by forest trees. In P-rich and P-poor beech (Fagus sylvatica) forests, naturally grown, young trees were girdled and used to determine root, ectomycorrhizal and microbial activities related to P mobilisation in the organic layer and mineral topsoil in comparison with those in nongirdled trees. After girdling, root carbohydrate reserves decreased. Root phosphoenolpyruvate carboxylase activities linking carbon and P metabolism increased. Root and ectomycorrhizal phosphatase activities and the abundances of bacterial genes catalysing major steps in P turnover increased, but soil enzymes involved in P mobilisation were unaffected. The physiological responses to girdling were stronger in P-poor than in P-rich forests. P uptake was decreased after girdling. The soluble and total P concentrations in roots were stable, but fine root biomass declined after girdling. Our results support that carbohydrate depletion results in reduced P uptake, enhanced internal P remobilisation and root biomass trade-off to compensate for the P shortage. As reductions in root biomass render trees more susceptible to drought, our results link tree deterioration with disturbances in the P supply as a consequence of decreased belowground carbohydrate allocation.

Bacterial colonization of minerals in grassland soils is selective and highly dynamic.

Bacteria colonize reactive minerals in soils where they contribute to mineral weathering and transformation. So far, the specificity, patterns and dynamics of mineral colonization have rarely been assessed under natural conditions. High throughput Illumina sequencing was employed to investigate the bacterial communities assembling on illite and goethite during exposure to natural grassland soils. Two different types of organic carbon sources, simple carbon compounds representing root exudates and detritus of two dominant grassland plant species were applied, and their effects on the temporal dynamics of bacterial communities were investigated. The observed temporal patterns suggest that the surfaces of de novo exposed minerals in soils drive the establishment of bacterial communities and override the effect of the type of carbon sources and of other environmental properties. Mineral colonization was selective and specific bacterial sequence variants exhibited distinct colonization patterns, among which early, intermittent, and late colonizers could be distinguished. Based on our results, soil minerals are not only colonized by specific bacterial communities but enable a succession of different bacterial communities. Our results thereby expand the concept of the mineralosphere and provide novel insights into mechanisms of community assembly in the soil ecosystem.

Unraveling spatiotemporal variability of arbuscular mycorrhizal fungi in a temperate grassland plot.

Soils provide a heterogeneous environment varying in space and time; consequently, the biodiversity of soil microorganisms also differs spatially and temporally. For soil microbes tightly associated with plant roots, such as arbuscular mycorrhizal fungi (AMF), the diversity of plant partners and seasonal variability in trophic exchanges between the symbionts introduce additional heterogeneity. To clarify the impact of such heterogeneity, we investigated spatiotemporal variation in AMF diversity on a plot scale (10 × 10 m) in a grassland managed at low intensity in southwest Germany. AMF diversity was determined using 18S rDNA pyrosequencing analysis of 360 soil samples taken at six time points within a year. We observed high AMF alpha- and beta-diversity across the plot and at all investigated time points. Relationships were detected between spatiotemporal variation in AMF OTU richness and plant species richness, root biomass, minimal changes in soil texture and pH. The plot was characterized by high AMF turnover rates with a positive spatiotemporal relationship for AMF beta-diversity. However, environmental variables explained only ≈20% of the variation in AMF communities. This indicates that the observed spatiotemporal richness and community variability of AMF was largely independent of the abiotic environment, but related to plant properties and the cooccurring microbiome.

Root exudation of mature beech forests across a nutrient availability gradient: the role of root morphology and fungal activity.

Root exudation is a key plant function with a large influence on soil organic matter dynamics and plant-soil feedbacks in forest ecosystems. Yet despite its importance, the main ecological drivers of root exudation in mature forest trees remain to be identified. During two growing seasons, we analyzed the dependence of in situ collected root exudates on root morphology, soil chemistry and nutrient availability in six mature European beech (Fagus sylvatica L.) forests on a broad range of bedrock types. Root morphology was a major driver of root exudation across the nutrient availability gradient. A doubling of specific root length exponentially increased exudation rates of mature trees by c. 5-fold. Root exudation was also closely negatively related to soil pH and nitrogen (N) availability. At acidic and N-poor sites, where fungal biomass was reduced, exudation rates were c. 3-fold higher than at N- and base-richer sites and correlated negatively with the activity of enzymes degrading less bioavailable carbon (C) and N in the bulk soil. We conclude that root exudation increases on highly acidic, N-poor soils, in which fungal activity is reduced and a greater portion of the assimilated plant C is shifted to the external ecosystem C cycle.

Discontinuity in the responses of ecosystem processes and multifunctionality to altered soil community composition.

Ecosystem management policies increasingly emphasize provision of multiple, as opposed to single, ecosystem services. Management for such "multifunctionality" has stimulated research into the role that biodiversity plays in providing desired rates of multiple ecosystem processes. Positive effects of biodiversity on indices of multifunctionality are consistently found, primarily because species that are redundant for one ecosystem process under a given set of environmental conditions play a distinct role under different conditions or in the provision of another ecosystem process. Here we show that the positive effects of diversity (specifically community composition) on multifunctionality indices can also arise from a statistical fallacy analogous to Simpson's paradox (where aggregating data obscures causal relationships). We manipulated soil faunal community composition in combination with nitrogen fertilization of model grassland ecosystems and repeatedly measured five ecosystem processes related to plant productivity, carbon storage, and nutrient turnover. We calculated three common multifunctionality indices based on these processes and found that the functional complexity of the soil communities had a consistent positive effect on the indices. However, only two of the five ecosystem processes also responded positively to increasing complexity, whereas the other three responded neutrally or negatively. Furthermore, none of the individual processes responded to both the complexity and the nitrogen manipulations in a manner consistent with the indices. Our data show that multifunctionality indices can obscure relationships that exist between communities and key ecosystem processes, leading us to question their use in advancing theoretical understanding--and in management decisions--about how biodiversity is related to the provision of multiple ecosystem services.

Estimates of Soil Bacterial Ribosome Content and Diversity Are Significantly Affected by the Nucleic Acid Extraction Method Employed.

Modern sequencing technologies allow high-resolution analyses of total and potentially active soil microbial communities based on their DNA and RNA, respectively. In the present study, quantitative PCR and 454 pyrosequencing were used to evaluate the effects of different extraction methods on the abundance and diversity of 16S rRNA genes and transcripts recovered from three different types of soils (leptosol, stagnosol, and gleysol). The quality and yield of nucleic acids varied considerably with respect to both the applied extraction method and the analyzed type of soil. The bacterial ribosome content (calculated as the ratio of 16S rRNA transcripts to 16S rRNA genes) can serve as an indicator of the potential activity of bacterial cells and differed by 2 orders of magnitude between nucleic acid extracts obtained by the various extraction methods. Depending on the extraction method, the relative abundances of dominant soil taxa, in particular Actino bacteria and Proteobacteria, varied by a factor of up to 10. Through this systematic approach, the present study allows guidelines to be deduced for the selection of the appropriate extraction protocol according to the specific soil properties, the nucleic acid of interest, and the target organisms.

Resource Type and Availability Regulate Fungal Communities Along Arable Soil Profiles.

Soil fungi play an essential role in the decomposition of plant-derived organic material entering soils. The quality and quantity of organic compounds vary seasonally as well as with soil depth. To elucidate how these resources affect fungal communities in an arable soil, a field experiment was set up with two plant species, maize and wheat. Resource availability was experimentally manipulated by maize litter input on one half of these maize and wheat plots after harvest in autumn. Fungal biomass was determined by ergosterol quantification, and community structure was investigated by fungal automated ribosomal intergenic spacer analysis (F-ARISA). An annual cycle was assessed across a depth gradient, distinguishing three soil habitats: the plough layer, rooted soil below the plough layer, and deeper root-free soil. Fungal communities appeared highly dynamic and varied according to soil depth and plant resources. In the plough layer, the availability of litter played a dominant role in shaping fungal communities, whereas in the rooted layer below, community structure and biomass mainly differed between plant species. This plant effect was also extended into the root-free soil at a depth of 70 cm. In winter, the availability of litter also affected fungal communities in deeper soil layers, suggesting vertical transport processes under fallow conditions. These distinct resource effects indicate diverse ecological niches along the soil profile, comprising specific fungal metacommunities. The recorded responses to both living plants and litter point to a central role of fungi in connecting primary production and decomposition within the plant-soil system.

Effectiveness of bio-effectors on maize, wheat and tomato performance and phosphorus acquisition from greenhouse to field scales in Europe and Israel: a meta-analysis.

Biostimulants (Bio-effectors, BEs) comprise plant growth-promoting microorganisms and active natural substances that promote plant nutrient-acquisition, stress resilience, growth, crop quality and yield. Unfortunately, the effectiveness of BEs, particularly under field conditions, appears highly variable and poorly quantified. Using random model meta-analyses tools, we summarize the effects of 107 BE treatments on the performance of major crops, mainly conducted within the EU-funded project BIOFECTOR with a focus on phosphorus (P) nutrition, over five years. Our analyses comprised 94 controlled pot and 47 field experiments under different geoclimatic conditions, with variable stress levels across European countries and Israel. The results show an average growth/yield increase by 9.3% (n=945), with substantial differences between crops (tomato > maize > wheat) and growth conditions (controlled nursery + field (Seed germination and nursery under controlled conditions and young plants transplanted to the field) > controlled > field). Average crop growth responses were independent of BE type, P fertilizer type, soil pH and plant-available soil P (water-P, Olsen-P or Calcium acetate lactate-P). BE effectiveness profited from manure and other organic fertilizers, increasing soil pH and presence of abiotic stresses (cold, drought/heat or salinity). Systematic meta-studies based on published literature commonly face the inherent problem of publication bias where the most suspected form is the selective publication of statistically significant results. In this meta-analysis, however, the results obtained from all experiments within the project are included. Therefore, it is free of publication bias. In contrast to reviews of published literature, our unique study design is based on a common standardized protocol which applies to all experiments conducted within the project to reduce sources of variability. Based on data of crop growth, yield and P acquisition, we conclude that application of BEs can save fertilizer resources in the future, but the efficiency of BE application depends on cropping systems and environments.

A slow-fast trait continuum at the whole community level in relation to land-use intensification.

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.

The supply of multiple ecosystem services requires biodiversity across spatial scales.

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.

13C assimilation as well as functional gene abundance and expression elucidate the biodegradation of glyphosate in a field experiment.

Glyphosate (N-phosphonomethylglycine; GLP) and its main metabolite AMPA (aminomethylphosphonic acid), are frequently detected in relatively high concentrations in European agricultural topsoils. Glyphosate has a high sorption affinity, yet it can be detected occasionally in groundwater. We hypothesized that shrinkage cracks occurring after dry periods could facilitate GLP transport to greater depths where subsoil conditions slow further microbial degradation. To test this hypothesis, we simulated a heavy rainfall event (HRE) on a clay-rich arable soil. We applied 2.1 kg ha-1 of 100% 13C3, 15N-labeled GLP one day before the simulated rainfall event. Microbial degradation of translocated GLP over a 21-day period was assessed by quantifying 13C incorporation into phospholipid fatty acids. Microbial degradation potential and activity were determined by quantifying the abundance and expression of functional genes involved in the two known degradation pathways of GLP; to AMPA (goxA) or sarcosine (sarc). We confirmed that goxA transcripts were elevated in the range of 4.23 x 105 copy numbers g-1 soil only one day after application. The increase in AMPA associated with a rise in goxA transcripts and goxA-harboring microorganisms indicated that the degradation pathway to AMPA dominated. Based on 13C-enrichment 3 h after the HRE, fungi appeared to initiate glyphosate degradation. At later time points, Gram+-bacteria proved to be the main degraders due to their higher 13C-incorporation. Once GLP reached the subsoil, degradation continued but more slowly. By comparing GLP distribution and its microbial degradation in macropores and in the bulk soil, we demonstrated different time- and depth-dependent GLP degradation dynamics in macropores. This indicates the need for field studies in which soil properties relevant to GLP degradation are related to limiting environmental conditions, providing a realistic assessment of GLP fate in soils.

Heavy rainfall following a summer drought stimulates soil redox dynamics and facilitates rapid and deep translocation of glyphosate in floodplain soils.

We present field data on the effects of heavy rainfall after drought on the mobility of glyphosate and redox conditions in a clayey floodplain soil. By applying glyphosate together with deuterated water as conservative tracer in combination with time resolved in situ redox potential measurements, the spatial and temporal patterns of water infiltration and pesticide transport as well as the concomitant changes of the redox conditions were revealed. Our findings demonstrate that shrinkage cracks in dry soils can serve as effective transport paths for atmospheric oxygen, water and glyphosate. The rain intensity of a typical summer storm event (approx. 25 mm within one hour) was sufficient to translocate deuterated water and glyphosate to the subsoil (50 cm) within 2 hours. Soil wetting induced partial closure of the shrinkage cracks and stimulated microbial activity resulting in pronounced dynamics of in situ soil redox conditions. Redox potentials in 40 to 50 cm depth dropped permanently to strongly reducing conditions within hours to days but fluctuated between reducing and oxidizing conditions in 10 to 30 cm depth. Our findings highlight the close link between the presence of macropores (shrinkage cracks), heavy rainfall after drought, redox dynamics and pesticide translocation to the subsoil and thus call for further studies addressing the effects of dynamic redox conditions as a limiting factor for glyphosate degradation.

Enzyme kinetics inform about mechanistic changes in tea litter decomposition across gradients in land-use intensity in Central German grasslands.

Grassland ecosystems provide important ecosystem services such as nutrient cycling and primary production that are affected by land-use intensity. To assess the effects of land-use intensity, operational and sensitive ecological indicators that integrate effects of grassland management on ecosystem processes such as organic matter turnover are needed. Here, we investigated the suitability of measuring the mass loss of standardized tea litter together with extracellular enzyme kinetics as a proxy of litter decomposition in the topsoil of grasslands along a well-defined land-use intensity gradient (fertilization, mowing, grazing) in Central Germany. Tea bags containing either green tea (high-quality litter) or rooibos tea (low-quality litter) were buried in 5 cm soil depth. Litter mass loss was measured after three (early-stage decomposition) and 12 months (mid-stage decomposition). Based on the fluorescence measurement of the reaction product 4-methylumbelliferone, Michaelis-Menten enzyme kinetics (Vmax: potential maximum rate of activity; Km: substrate affinity) of five hydrolases involved in the carbon (C)-, nitrogen (N)- and phosphorus (P)-cycle (ß-glucosidase (BG), cellobiohydrolase (CBH), cellotriohydrolase (CTH), 1,4-ß-N-acetylglucosaminidase (NAG), and phosphatase (PH)) were determined in tea litter bags and in the surrounding soil. The land-use intensity index (LUI), summarizing fertilization, mowing, grazing, and in particular the frequency of mowing were identified as important drivers of early-stage tea litter decomposition. Mid-stage decomposition was influenced by grazing intensity. The higher the potential activity of all measured C-, N- and P-targeting enzymes, the higher was the decomposition of both tea litters in the early-phase. During mid-stage decomposition, individual enzyme parameters (Vmax of CTH and PH, Km of CBH) became more important. The tea bag method proved to be a suitable indicator which allows an easy and cost-effective assessment of land-use intensity effects on decay processes in manged grasslands. In combination with enzyme kinetics it is an appealing approach to identify mechanisms driving litter break down.

Soil phosphorus status and P nutrition strategies of European beech forests on carbonate compared to silicate parent material.

Sustainable forest management requires understanding of ecosystem phosphorus (P) cycling. Lang et al. (2017) [Biogeochemistry, https://doi.org/10.1007/s10533-017-0375-0] introduced the concept of P-acquiring vs. P-recycling nutrition strategies for European beech (Fagus sylvatica L.) forests on silicate parent material, and demonstrated a change from P-acquiring to P-recycling nutrition from P-rich to P-poor sites. The present study extends this silicate rock-based assessment to forest sites with soils formed from carbonate bedrock. For all sites, it presents a large set of general soil and bedrock chemistry data. It thoroughly describes the soil P status and generates a comprehensive concept on forest ecosystem P nutrition covering the majority of Central European forest soils. For this purpose, an Ecosystem P Nutrition Index (ENI P ) was developed, which enabled the comparison of forest P nutrition strategies at the carbonate sites in our study among each other and also with those of the silicate sites investigated by Lang et al. (2017). The P status of forest soils on carbonate substrates was characterized by low soil P stocks and a large fraction of organic Ca-bound P (probably largely Ca phytate) during early stages of pedogenesis. Soil P stocks, particularly those in the mineral soil and of inorganic P forms, including Al- and Fe-bound P, became more abundant with progressing pedogenesis and accumulation of carbonate rock dissolution residue. Phosphorus-rich impure, silicate-enriched carbonate bedrock promoted the accumulation of dissolution residue and supported larger soil P stocks, mainly bound to Fe and Al minerals. In carbonate-derived soils, only low P amounts were bioavailable during early stages of pedogenesis, and, similar to P-poor silicate sites, P nutrition of beech forests depended on tight (re)cycling of P bound in forest floor soil organic matter (SOM). In contrast to P-poor silicate sites, where the ecosystem P nutrition strategy is direct biotic recycling of SOM-bound organic P, recycling during early stages of pedogenesis on carbonate substrates also involves the dissolution of stable Ca-Porg precipitates formed from phosphate released during SOM decomposition. In contrast to silicate sites, progressing pedogenesis and accumulation of P-enriched carbonate bedrock dissolution residue at the carbonate sites promote again P-acquiring mechanisms for ecosystem P nutrition. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10533-021-00884-7.