• Improved estimation of karst soil thickness at the landform scale. • Rocky desertification indexes are key factors in predicting soil thickness. • Quantile regression forests effectively models soil thickness variation. Soil thickness is a basic feature of the earth’s land surface. Accurately representing the spatial distribution of soil thickness is important for various models of earth surface processes. However, mapping soil thickness in karst landforms is highly uncertain. To address this challenge, this study analyzed the correlation between 906 soil thickness measurements and 376 environmental characteristics in a typical karst landscape covering 54,000 km 2 . We employed a quantile regression forests (QRF) approach to estimate soil thickness and evaluate the associated uncertainty in the predicted results. We found that, like other regional scale soil mapping models, climate and topographic data were key factors influencing soil thickness. Specific for karst landscapes, we found that the characteristics of karst rocky desertification play a key role in predicting soil thickness. The rocky desertification information indexes (RIs), which use exposure rate of bedrock to represent the degree of karst rocky desertification, showed relatively high importance in the variable importance assessment. The developed model explained 40 % of the spatial variability of soil thickness across the study area, with an RMSE (37.3 cm) of 50–60 % of the mean thickness. This indicates that the model, and environmental factors evaluated within, explained a little less than half of the spatial variability. The prediction results reveal the distribution pattern of soil thickness at both regional and local scales within karst landforms. Thick soil was commonly found in low-lying landscape features like depressions and foothills, whereas areas with steep slopes, ridges, and peaks tended to have thin soil, following a typical toposequence. In areas with relatively deep soil or severe rocky desertification, the uncertainty of predicting soil thickness is relatively high. The results of uncertainty analysis, as a supplement to the prediction results, have improved the usability of the predictions to a certain extent. This study has, to some extent, addressed the challenges of predicting soil thickness in karst areas and has also provided transferable methods for other complex regions.

Understanding how fertilizer phosphorus (P) interacts with soils is necessary in order to use it efficiently. In the long-term field experiment CRUCIAL (Closing the Rural-Urban Nutrient Cycle − Investigations through Agronomic Long-term experiments), organic fertilizers were intentionally overapplied to test soil ecotoxicological limits. This has resulted in yearly P inputs of up to 463 kg·ha−1 and positive P balances (input after crop offtake) for over 20 years. These inputs have occurred in sandy loam soils. Fertilization treatments included sewage sludge, compost, cattle manure, other organic fertilizers, and mineral NPK. We hypothesized that, given the high fertilizer P inputs, P accumulation in the topsoil (0–0.2 m), along with its distribution into sequentially extractable fractions, would vary depending on P fractions in the fertilizers. We measured P fractions and total P concentrations in both organic fertilizers and topsoils, and calculated two P budgets. The first budget compared topsoil total P concentrations from 2003 with those from 2022, considering the total fertilizer P inputs and crop offtake over that time. The second is a fractional P budget that uses P fractions in topsoils treated with NPK as a baseline to assess fertilization induced changes. Treatments with sludge, compost, or manure had positive P balances between 2152 and 2664 kg·ha−1 over 20 years. Total P stocks in the topsoil increased by at least 869 kg·ha−1 in treatments with sludge or compost compared to only 278 kg·ha−1 with manure. Treatments supplying less resin extractable-P and more NaHCO3-P or NaOH-P retained a higher proportion of the fertilizer P, even in topsoils already saturated with P. Consequently, specific organic fertilizers have caused increases in soil P fractions corresponding to their own P fraction compositions. Still, between 59–87 % of the excess P applied could not be accounted for in topsoils after considering crop P offtake. Consequently, regardless of the fertilizer type, overfertilization led to excess P movement out of the topsoil layer, which is detrimental for the environment.

• Bacterial community compositions on the porous surfaces different from original soil communities. • Early colonizers on the surfaces are not random. • Active motility and chemotactic movement are two primary characteristics facilitating microbial early-stage colonization. • A trade-off between the growth and dispersal rates regulated early-stage colonization. • The trade-off between the growth and dispersal rates maintain the biodiversity colonizing new niches. Microbial dispersal and subsequent colonization of new niches are fundamental processes in microbial ecology, particularly in patchy environments like soil. However, the heterogeneity of soil pore spaces and the resulting fragmented aqueous habitats are known to significantly impede microbial dispersal rates and ranges. Despite this, the strategies microbes employ to overcome these abiotic constraints remain poorly understood. To address this, we developed a novel experimental system using porous ceramic surfaces to simulate hydrated soil environments, enabling direct quantification of early-stage bacterial colonization. Our findings reveal that distinct taxonomic and functional bacterial populations successfully colonized the porous ceramic surfaces, differing significantly from the original soil communities. Active motility and chemotaxis emerged as two key traits facilitating early-stage colonization. However, the advantages conferred by motility and chemotaxis were significantly reduced under drier soil conditions, typically at water contents below 25% (v/v). Under such conditions, non-motile bacteria relied on passive dispersal mechanisms or physical adhesion to colonize the porous surfaces. Furthermore, functional metagenomic profiling of the colonizing microbial populations uncovered a trade-off between growth and dispersal rates. This observed trade-off was incorporated into an agent-based model simulating microbial activity in soil, which explored how correlations between microbial functional genes influence community dynamics during early colonization. The simulations demonstrated that the growth-dispersal trade-off is crucial for enhancing and maintaining microbial diversity during colonization of new niches. Our study elucidates the key biophysical mechanisms driving microbial early-stage colonization dynamics from bulk soil to new environments, highlighting this process as a core ecological phenomenon in soil ecosystems.

• Forest conversion decreased soil total N storage and ammonium content. • Forest conversion increased soil autotrophic nitrification and N 2 O emissions. • Forest conversion decreased gross N mineralization and microbial biomass. • Soil (BD and carbon) and climatic (MAT and MAP) properties were indirectly altering soil N cycling. Understanding soil nitrogen (N) storage and loss following forest conversion is crucial to evaluate land resource utilization and environmental impacts. However, forest conversion altering soil N dynamics and nitrous oxide (N 2 O) emissions and their driving factors remain largely unknown. Here, we conducted a global meta -analysis of 97 published papers to evaluate the effect of forest conversion (e.g., conversion of primary forests to secondary forests, managed plantations, grasslands, or croplands) on soil N transformations and N 2 O emissions. We found that forest conversion decreased gross N mineralization and ammonium concentration due to reduced soil microbial biomass, total carbon, and total N. Conversely, forest conversion overall increased autotrophic nitrification and N 2 O emissions due to the increased ammonia-oxidizing bacteria and archaea abundances. Primary forest converting to croplands and plantations notably increased soil N 2 O emissions in temperate and tropical zones. Structural equation model showed that increased ammonium and nitrate levels, and decreased total carbon were the main factors inducing soil N 2 O emissions in unfertilized ecosystems, while the increased nitrate was a key factor inducing soil N 2 O emissions in fertilized ecosystems. Altogether, our results suggest that forest conversion overall limits soil N storage while stimulating N 2 O emissions, highlighting the importance of conserving primary forests to reduce N losses and the negative impacts on the environment.

• Soil carbonates (SIC) neutralization by N fertilization releases significant CO 2 . • A balanced fertilization (NPK) reduces soil carbonate-derived CO 2 emission. • The protective effects of SIC keep organic carbon (SOC) decomposition low. • Complete soil decalcification induces decomposition of SOC. • Following decalcification, soil CO 2 emission directly is controlled by nutrient availability. Decalcification, especially due to acidity induced by nitrogen (N) fertilization, generates an often-underestimated source of atmospheric CO 2 in agroecosystems. Complete depletion of soil inorganic carbon (SIC), i.e. carbonates, intensifies the decomposition of soil organic carbon (SOC) to an extent not yet experimentally demonstrated. Six fertilization management practices including application of urea, urea + superphosphate + potassium chloride, ammonium phosphate, ammonium phosphate + potassium chloride, chicken manure along a control i.e. no fertilization were used to quantify the effects of N fertilization on soil acidification and the percentage of SIC-originated CO 2 in total soil CO 2 emissions. Gas samples were collected during a 56-day incubation experiment to determine total emitted CO 2 and its δ 13 C value. The presence of SIC, kept the total CO 2 emissions after inorganic fertilization at levels comparable to unfertilized soil and a balanced fertilization reduced SIC-originated CO 2 emissions ( ≈ 15 % after NPK vs. 35 % with N applications) due to better nutrient use efficiency and comparatively less proton generation after nitrification. When inorganic N fertilization led to complete SIC depletion after shifting in soil pH from circumneutral (pH = 7.4) to slightly-moderately acidic pH (pH = 6.5 to about 5.8) ranges, a sudden increase in total CO 2 emissions indicated the loss of the protective effects of SIC, and the extreme decomposition of the indigenous SOC. Complete depletion of SIC activates a negative feedback loop: the more fertilizer is added for more crop production, the more SOC, and soil productivity will be lost. We conclude that balanced fertilization and the use of organic fertilizers not only ensure sustainable productivity, but also significantly reduce CO 2 emissions from agroecosystems by preventing SIC depletion.

• Organic root exudate compounds (ORECs) enhance Si solubilisation from soils. • Si extraction efficiency of ORECs varies among soils and soil minerals. • Catechol, citrate, and oxalate solubilise Si from different soil Si pools. • ORECs enhance nutrient solubilisation and soil weathering. Organic root exudate compounds (ORECs) can enhance mineral dissolution, releasing silicon (Si), but OREC-induced processes of Si solubilisation from different soil Si pools are poorly understood. This study explored the impact of two carboxylates (citrate, oxalate) and a phenolate (catechol) on Si solubilisation from soils and soil minerals. We extracted six different soils, seven primary minerals, and four clay minerals with the three ORECs and NH 4 NO 3 as a background electrolyte (control) at a realistic rhizosphere concentration of 5 mmol L −1 . The extraction solutions were not buffered to mimic the conditions of real rhizospheres. Silicon extractability from the experimental soils was positively related to clay content, whereas other soil chemical and mineral characteristics showed no obvious relation. The ORECs extracted up to 11 times more Si than the control from primary minerals, clay minerals and soils during 2-hour extraction periods. Citrate consistently increased Si solubility in soils and soil minerals. Catechol mainly increased Si solubilisation from soil minerals, while oxalate had the greatest effect in soils. Overall, the Si solubilisation efficiency of ORECs varied and followed the order citrate > catechol > oxalate for primary minerals, catechol > citrate > oxalate for clay minerals, and oxalate > citrate > catechol for soils. We conclude that ORECs can strongly enhance Si solubilisation from soils and soil minerals at concentrations as low as observed in plant rhizospheres. These OREC-induced mineral weathering processes contribute to Si dynamics in the rhizosphere and facilitate soil formation.

• Layered Technosols composed of organic and mineral urban wastes. • Over 3 years, early pedogenesis processes as in natural soils but much faster. • Biodegradation and shrinkage play a key role in this first phase of pedogenesis. • Important transfers of particles and solutes were observed down the profiles. • A trade-off between organic wastes biodegradation and stabilization. Constructed soils based on urban waste, i.e. Technosols appear as a promising solution to enhance circular economy while delivering ecosystem services. Their ability to provide such services depend on their constitution as well as on their temporal evolution and pedogenesis, which is poorly known. We studied during three years the changes in an isolatic Technosol made essentially of organic urban wastes. The study took place on a Parisian rooftop with an experimental trial of 24 plots. We compared four Technosols with similar upper layers (a mix of biowaste compost and spent mushroom substrate), but with either a mineral (shredded tiles and bricks) or an organic lower layer (shredded wood). Both types were run with and without plants. Technosols were monitored over three years and samples were taken at different times to study pedogenetic processes. We observed a rapid and sharp volume loss of the Technosols, responsible for an important mass loss, but not leading to any increase in bulk density. A clear physico-chemical differentiation of treatments from the parent materials appeared after one and three years. The Technosoil organic C stocks decreased over time. During three years, all Technosols were a net source of nitrogen and dissolved organic carbon, released in the drainage waters. Identified pedogenesis processes were the same as in natural soils, but the changes were very fast. The key equilibrium between mineralisation of organic matter and its stabilization that must be ensured when creating such Technosols. They show the necessity for long term research on the development of Technosols.