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Increased understanding of the stabilization mechanisms of the organic matter (OM) entering the soil system through the application of organic amendments is of paramount agronomic and environmental importance. Here, we examined the organic C and total N distribution in OM pools (i.e. free, intra-macroaggregate, intra-microaggregate, mineral-associated, dissolved, and humic acid fractions) characterized by different protection mechanisms in soils annually amended with different organic substrates of municipal origin (i.e. municipal solid waste compost, sewage sludge compost, and thermally dried sewage sludge) for three years. With respect to the unamended control soil, the application of the three organic materials, especially thermally dried sewage sludge, increased soil organic C, and total N contents. The organic inputs accumulated mostly in the physically unprotected free OM pool, as relatively fresh, low humified materials, and secondarily in the intra-macroaggregate fraction, as partially decomposed OM weakly protected by physical mechanisms. Our results suggest that mechanisms related to strong physical protection in microaggregates and chemical inaccessibility by intimate association with minerals do not govern OM stabilization in the short term. [ABSTRACT FROM AUTHOR]

• We investigated Fe speciation in fine sand (FSa) and fine silt plus clay (FSi + Cl). • The nature of Fe-SOM interactions vary with soil particle size and land use. • FSa fractions were characterized by more crystalline Fe phases, including goethite. • FSi + Cl fractions exhibit the presence of ferrihydrite. • SOM in the FSi + Cl fraction is more thermodynamically stable than in FSa. Iron (Fe) (oxyhydr)oxides represent a significant phase for the organic carbon (OC) stabilization. Due to their high surface areas, short-range-ordered Fe minerals, like ferrihydrite, show a higher ability to stabilize OC than crystalline secondary minerals, like lepidocrocite, goethite, and magnetite. However, how Fe phases and their crystallinity relate to soil organic matter (SOM) composition is still not completely known. We investigated Fe solid phase speciation in two soil particle size fractions (i.e., fine sand — FSa — and fine silt and clay — FSi + Cl —), isolated from coniferous (CF) and broadleaved forest soils (BF), grassland soils (GL), and technosols (TS). All samples were characterized by Fe K-edge extended X-ray absorption fine structure (EXAFS) and X-ray diffraction, and a subset by 57Fe Mössbauer spectroscopy. Further, ramped combustion thermal analyses (coupled differential scanning calorimetry (DSC) and CO 2 evolved gas analysis (CO 2 -EGA)) were used to evaluated SOM stability. With the only exception of TS, goethite was the main Fe phase in FSa fractions, whereas less crystalline phases (i.e., ferrihydrite, based on EXAFS) dominated the FSi + Cl fractions. The proportion of goethite and ferrihydrite in both fractions decreased with increasing OC content, while that of Fe(III)-SOM in FSa increased with increasing OC content. Mössbauer and EXAFS data clearly indicated a presence of hematite in GL soils. Our data suggest that more crystalline Fe forms, like goethite and hematite, may be important for OC abundance in the FSa fraction and in soils with high OC contents, like GL. Thermal analysis showed the dominance of mineral associated organic matter in low-OC soils, and of plant residues in high-OC soils. As a whole, we posit that the FSi + Cl fractions contain Fe phases of less crystallinity because of presumed association with SOM, and that SOM in the FSi + Cl fraction is also more thermodynamically stable than in FSa, although differences are observed across land uses. Our observations suggest that the nature of Fe-SOM interactions can vary substantially with soil particle size and land use, which has important implication for SOM persistence. [ABSTRACT FROM AUTHOR]

Abstract: Conservation tillage practices that entail no or reduced soil disturbance are known to help preserve or accumulate soil organic matter (OM). However, the underlying mechanisms especially at the molecular level are not well understood. In this study soil samples from 25-year-old experimental plots continuously cropped with barley (Hordeum vulgare L.) under no-tillage (NT) and chisel tillage (CT) were subjected to a new physical fractionation method to isolate dissolved OM, mineral-free particulate OM located outside aggregates (physically and chemically unprotected), OM occluded within both macroaggregates and microaggregates (weakly and strongly protected by physical mechanisms, respectively), and OM in intimate association with minerals (protected by chemical mechanisms). The whole soils and OM fractions were analyzed for organic C and N content and by modern nuclear magnetic resonance (NMR) techniques. The soil under NT stored 16% more organic C and 5% more N than the soil under CT. Compared to CT, NT increased free organic C content by 7%, intra-macroaggregate organic C content by 20%, intra-microaggregate organic C content by 63%, and mineral-associated organic C content by 16% and decreased dissolved organic C content by 11%. The mineral-associated OM pool accounted for 65% of the difference in total organic C content between NT and CT, whereas the intra-microaggregate OM only explained 18%, intra-macroaggregate OM 14%, and free OM 11%. The NMR experiments revealed that the free and intra-aggregate OM fractions were dominated by crop-derived materials at different stages of decomposition, whereas the mineral-associated OM pool was predominately of microbial origin. Overall, our results indicate that microbes and microbial by-products associated with mineral surfaces and likely physically protected by entrapment within very small microaggregates constitute the most important pool of OM stabilization and C sequestration in soils under NT. Most probably the slower macroaggregate turnover in NT relative to CT boosts not only the formation of microaggregates and thereby the physical protection of crop-derived particulate OM, but more importantly the interaction between mineral particles and microbial material that results in the formation of very stable organo-mineral complexes. [Copyright &y& Elsevier]

The objective of this work was to describe a method for isolating meaningful and measurable soil organic matter (SOM) pools that differ in the mechanisms by which they are protected from decomposition. The proposed method is appropriate for soil C stabilization and sequestration studies. Unlike previous fractionation schemes, this procedure allows free SOM located between aggregates (unprotected C pool) and SOM occluded within both macroaggregates and microaggregates (C weakly and strongly protected by physical mechanisms, respectively) to be recovered separately, freed from the soil mineral matrix and the mineral-associated SOM pool (C pool protected by chemical mechanisms) and thus well suited to advanced chemical characterization by 13C-NMR. Briefly, free SOM is isolated by an initial density separation. Stable macroaggregates are broken up into stable microaggregates and intra-macroaggregate SOM, which is then separated by density. Finally, intra-microaggregate SOM is isolated from mineral-associated SOM by a third density separation after ultrasonic disruption. The SOM dissolved during the fractionation procedure is also recovered. Results obtained on soil samples with contrasting textures suggested that clay content induces a decrease of the proportion of free organic C and an increase of mineral-associated organic C content. Free SOM is characterized by a marked presence of undecayed organic material and biologically labile substances, such as carbohydrates and proteins. In contrast, SOM occluded within aggregates, especially within microaggregates, represents a more decomposed fraction, relatively enriched in unsubstituted-aliphatic material, most probably lipid biopolymers. [ABSTRACT FROM AUTHOR]

Abstract: The use of organic municipal wastes as soil amendments is an increasing practice that can divert significant amounts of waste from landfill, and provides a potential source of nutrients and organic matter to ameliorate degraded soils. Due to the high heterogeneity of organic municipal waste streams, it is difficult to rapidly and cost-effectively establish their suitability as soil amendments using a single method. Thermal analysis has been proposed as an evolving technique to assess the stability and composition of the organic matter present in these wastes. In this study, three different organic municipal waste streams (i.e., a municipal waste compost (MC), a composted sewage sludge (CS) and a thermally dried sewage sludge (TS)) were characterized using conventional and thermal methods. The conventional methods used to test organic matter stability included laboratory incubation with measurement of respired C, and spectroscopic methods to characterize chemical composition. Carbon mineralization was measured during a 90-day incubation, and samples before and after incubation were analyzed by chemical (elemental analysis) and spectroscopic (infrared and nuclear magnetic resonance) methods. Results were compared with those obtained by thermogravimetry (TG) and differential scanning calorimetry (DSC) techniques. Total amounts of CO2 respired indicated that the organic matter in the TS was the least stable, while that in the CS was the most stable. This was confirmed by changes detected with the spectroscopic methods in the composition of the organic wastes due to C mineralization. Differences were especially pronounced for TS, which showed a remarkable loss of aliphatic and proteinaceous compounds during the incubation process. TG, and especially DSC analysis, clearly reflected these differences between the three organic wastes before and after the incubation. Furthermore, the calculated energy density, which represents the energy available per unit of organic matter, showed a strong correlation with cumulative respiration. Results obtained support the hypothesis of a potential link between the thermal and biological stability of the studied organic materials, and consequently the ability of thermal analysis to characterize the maturity of municipal organic wastes and composts. [Copyright &y& Elsevier]

Humic acids (HAs) isolated from sewage sludge (SS) and control and SS-amended soils were characterized by fluorescence spectroscopy. The main feature of fluorescence spectra was a broad band with the maximum centered at excitation/emission wavelengths that were much shorter for SS-HA (340/438 nm) than for any soil HA (440/510 nm). Titration with Cu(II), Zn(II), Cd(II), and Pb(II) ions decreased fluorescence intensities of HAs. Titration data were fitted to a single-site fluorescence quenching model, and metal ion complexing capacities of each HA sample and stability constants of metal ion-HA complexes were calculated. The binding capacities of HAs and strengths of metal ion-HA complexes followed the order Pb(II) > Cu(II) > Cd(II) > Zn(II). With respect to the control soil HA, SS-HA, which showed the smallest contents of acidic functional groups and the lowest humification degree, was characterized by much smaller binding capacities and stability constants. The binding capacities and affinities of SS-amended soil HA were intermediate between those of native soil HA and SS-HA but closer to the former, thus suggesting a partial incorporation of HA fractions of SS into native soil HAs. These effects are expected to have a great impact on the behavior of metals in SS-amended soils. [ABSTRACT FROM AUTHOR]

The soil acid-base buffering capacity and the biological availability, mobilization, and transport of macro- and micronutrients, toxic metal ions, and xenobiotic organic cations in soil are strongly influenced by the acid-base properties of humic substances, of which humic and fulvic acids are the major fractions. For these reasons, the proton binding behavior of the humic acid-like (HA) and fulvic acid-like (FA) fractions contained in a compost are believed to be instrumental in its successful performance in soil. In this work, the acid-base properties of the HAs and FAs isolated from a mixture of the sludge residue obtained from olive oil mill wastewater (OMW) evaporated in an open-air pond and tree cuttings (TC) at different stages of composting were investigated by a current potentiometric titration method and the nonideal competitive adsorption (NICA)-Donnan model. The N1CA-Donnan model provided an excellent description of the acid-base titration data, and pointed out substantial differences in site density and proton-binding affinity between the HAs and FAs examined. With respect to FAs, HAs were characterized by a smaller content of carboxylic- and phenotic-type groups and their larger affinities for proton binding. Further, HAs featured a greater heterogeneity in carboxylic-type groups than FAs. The composting process increased the content and decreased the proton affinity of carboxylic- and phenolic-type groups of HAs and FAs, and increased the heterogeneity of phenolic-type groups of HAs. As a whole, these effects indicated that the composting process could produce HA and FA fractions with greater cation binding capacities. These results suggest that composting of organic materials improves their agronomic and environmental value by increasing their potential to retain and exchange macro- and micronutrients, and to reduce the bioavailability of organic and inorganic pollutants. [ABSTRACT FROM AUTHOR]

Intercropping has garnered renewed attention in Europe as an agroecological practice to enhance environmental sustainability. Interest in plant-based proteins by increasing human consumption of legumes is gaining traction. Legume-cereal intercropping for dual seed production could offer environmental and economic advantages. However, barriers hinder widespread adoption by farmers. This study analyzes the results of seven focus groups with 220 diverse stakeholders. Barriers, enabling factors, and strategies for the adoption of grain legume-cereal intercropping were assessed to determine food system transition strategies. The five strategies for intercropping support related to farm, food, advice, governance, and network systems. Farmer-led, institutionally supported, and research-informed advice systems, effective governance, and increased networking would enable strategic pathways for regional food and feed production through intercropping. [ABSTRACT FROM AUTHOR]

• Molecular composition of DOM and leachates of potential DOM sources in the Harz. • Important differences in molecular features of plant materials and their leachates. • Polyphenol chemistry has the largest potential for identifying DOM sources. • Spruce wood-derived lignin probably a crucial DOM precursor in the Oder catchment. • New system-specific chemometric proxies of DOM sources from THM-GC–MS. Environmental change is increasing the concentration of dissolved organic matter (DOM) in catchments of the Northern Hemisphere. This study aims to assess the causes of high DOM concentrations in streams and reservoirs of the Harz National Park (Germany), by means of molecular characterization using thermally assisted hydrolysis and methylation (THM-GC–MS). In order to formulate proxies of the prevailing origin of the numerous THM products of polyphenols, carbohydrates, proteins, aliphatic macromolecules, resins and other DOM precursors, we created a reference sample set of potential sources (spruce, birch, blueberry, heather, peat moss, soils) from the area. Besides solid-state reference samples (bulk organic matter; BOM) we obtained and analyzed their leachates (water-extractable OM; WEOM). Finally, an existing THM-GC–MS dataset of the DOM from the Oder river, which crosses the boundary between peat and forest biomes in the Harz, was extended and explored chemometrically using Principal Component Analysis (PCA) to test the proxies for stream DOM assessment. The results show large differences between BOM and WEOM, which suggests that the solid-to-leachate transition is highly selective or significantly alters the major biomolecular constituents. THM compounds that tend to be more abundant in WEOM than in BOM are G-type phenolic compounds (1,2-dimethoxybenzenes, from lignin and tannin), nitrogen-containing moieties and benzene carboxylic acids, whereas WEOM is depleted in products of polysaccharides, syringyl lignin and aliphatic macromolecules (cutin and suberin). The lignin fingerprint of the WEOM also differs significantly from that of BOM, being depleted in the vast majority of the typical products of macromolecular lignin (G7, G8, G14, G15) and enriched in the acid moiety (G6, predominantly from vanillic acid), especially for spruce wood. THM chromatograms of DOM from the forest section of the Oder show an extraordinary abundance of G6, most probably from spruce-derived lignin. This may indicate a major role of DOM released from decaying spruce logs and forest soils. The results highlight both the potential and the pitfalls associated with source identification of DOM using THM-GC–MS. [ABSTRACT FROM AUTHOR]

The importance of soil age as an ecosystem driver across biomes remains largely unresolved. By combining a cross-biome global field survey, including data for 32 soil, plant, and microbial properties in 16 soil chronosequences, with a global meta-analysis, we show that soil age is a significant ecosystem driver, but only accounts for a relatively small proportion of the cross-biome variation in multiple ecosystem properties. Parent material, climate, vegetation and topography predict, collectively, 24 times more variation in ecosystem properties than soil age alone. Soil age is an important local-scale ecosystem driver; however, environmental context, rather than soil age, determines the rates and trajectories of ecosystem development in structure and function across biomes. Our work provides insights into the natural history of terrestrial ecosystems. We propose that, regardless of soil age, changes in the environmental context, such as those associated with global climatic and land-use changes, will have important long-term impacts on the structure and function of terrestrial ecosystems across biomes. Soil age is thought to be an important driver of ecosystem development. Here, the authors perform a global survey of soil chronosequences and meta-analysis to show that, contrary to expectations, soil age is a relatively minor ecosystem driver at the biome scale once other drivers such as parent material, climate, and vegetation type are accounted for. [ABSTRACT FROM AUTHOR]

Increases in the abundance of woody species have been reported to affect the provisioning of ecosystem services in drylands worldwide. However, it is virtually unknown how multiple biotic and abiotic drivers, such as climate, grazing, and fire, interact to determine woody dominance across global drylands. We conducted a standardized field survey in 304 plots across 25 countries to assess how climatic features, soil properties, grazing, and fire affect woody dominance in dryland rangelands. Precipitation, temperature, and grazing were key determinants of tree and shrub dominance. The effects of grazing were determined not solely by grazing pressure but also by the dominant livestock species. Interactions between soil, climate, and grazing and differences in responses to these factors between trees and shrubs were key to understanding changes in woody dominance. Our findings suggest that projected changes in climate and grazing pressure may increase woody dominance in drylands, altering their structure and functioning. [ABSTRACT FROM AUTHOR]

Physical fractionation methods used in soil organic matter (SOM) research commonly include density-based procedures with heavy liquids to separate SOM pools with varying turnover rates and functions. Once separated, the heavy SOM pools are often thoroughly rinsed with water to wash off any residues of the heavy liquids. Using four soils with contrasting properties, we investigated the effects of using either sodium polytungstate (SPT) or sodium iodide (NaI), two of the most commonly used heavy liquids, on the distribution of organic carbon (C) and total nitrogen (N) in free light, intra-aggregate light, and mineral-associated heavy SOM pools isolated by a common fractionation scheme. We also determined the effects of washing the mineral-associated heavy SOM fractions on the recovery of organic C and total N after separation. Because of its smaller viscosity compared to that of NaI, SPT consistently yielded greater intra-aggregate and smaller mineral-associated soil organic C contents. We also confirm that some commercial SPT products, such as the one used here, can contaminate organo-mineral heavy pools with N during density-based fractionation procedures. We do not recommend the repeated washing of heavy fractions separated with Na-based heavy liquids, as this can mobilize SOM. [ABSTRACT FROM AUTHOR]

The decline of soil organic matter (SOM) and micro and macronutrients is among the most serious threats that many agricultural soils in the world are facing. In many countries, soil amendments from a wide range of organic wastes are increasingly used as a win-win strategy to mitigate global warming while enhancing soil fertility and, in turn, food security. Digestate, a by-product of the anaerobic digestion, is often used as a fertilizer and an amendment. However, an in-depth understanding of its impacts on native SOM and organic carbon (OC) stabilization mechanisms is still needed. The aim of this work was to investigate the influence of solid vs. liquid digestates on both SOM accrual and distribution in particulate organic matter (POM) and mineral-associated organic matter (MAOM) pools, after 0, 3 and 6 months from their application. None of the amendments had significant effects on soil OC and total nitrogen concentrations and stocks. However, after 6 months, a clear difference in OC distribution between SOM pools was observed as a function of the digestate phase applied to soil. In particular, the MAOM to POM ratio decreased in the soil amended with solid digestate with respect to the unamended control soil, while this ratio did not differ following liquid digestate amendment. Thermal analysis suggested that the interaction between SOM and mineral surfaces, rather than the biochemical recalcitrance, is the major SOM stabilization mechanism in both unamended and amended soils. This study highlighted that a more in-depth evaluation of OC accrual through digestate application, especially in the short term, can be achieved by investigating functionally defined fractions rather than bulk SOM. [Display omitted] • Solid and liquid digestates had no significant effects on SOC concentration and stock. • Digestate phase affects SOC distribution between SOM pools. • The MAOM to POM ratio decreased in soil amended with solid digestate. • The MAOM to POM ratio in soil amended with liquid digestate and in the control was similar. • Further studies based on longer-term observations and multiple applications are needed. [ABSTRACT FROM AUTHOR]

Drylands (hyperarid, arid, semiarid, and dry subhumid ecosystems) cover almost half of Earth’s land surface and are highly vulnerable to environmental pressures. Here we provide an inventory of soil properties including carbon (C), nitrogen (N), and phosphorus (P) stocks within the current boundaries of drylands, aimed at serving as a benchmark in the face of future challenges including increased population, food security, desertification, and climate change. Aridity limits plant production and results in poorly developed soils, with coarse texture, low C:N and C:P, scarce organic matter, and high vulnerability to erosion. Dryland soils store 646 Pg of organic C to 2 m, the equivalent of 32% of the global soil organic C pool. The magnitude of the historic loss of C from dryland soils due to human land use and cover change and their typically low C:N and C:P suggest high potential to build up soil organic matter, but coarse soil textures may limit protection and stabilization processes. Restoring, preserving, and increasing soil organic matter in drylands may help slow down rising levels of atmospheric carbon dioxide by sequestering C, and is strongly needed to enhance food security and reduce the risk of land degradation and desertification. [ABSTRACT FROM AUTHOR]

The availability of metallic nutrients in dryland soils, many of which are essential for the metabolism of soil organisms and vascular plants, may be altered due to climate change-driven increases in aridity. Biocrusts, soil surface communities dominated by lichens, bryophytes and cyanobacteria, are ecosystem engineers known to exert critical functions in dryland ecosystems. However, their role in regulating metallic nutrient availability under climate change is uncertain. Here, we evaluated whether well-developed biocrusts modulate metallic nutrient availability in response to 7 years of experimental warming and rainfall reduction in a Mediterranean dryland located in southeastern Spain. We found increases in the availability of K, Mg, Zn and Na under warming and rainfall exclusion. However, the presence of a well-developed biocrust cover buffered these effects, most likely because its constituents can uptake significant quantities of available metallic nutrients. Our findings suggest that biocrusts, a biotic community prevalent in drylands, exert an important role in preserving and protecting metallic nutrients in dryland soils from leaching and erosion. Therefore, we highlight the need to protect them to mitigate undesired effects of soil degradation driven by climate change in this globally expanding biome. Eduardo Moreno-Jiménez et al. experimentally manipulate rainfall and temperature in a Mediterranean dryland to explore the association of biocrusts with essential metallic nutrients. They find that biocrusts—communities of lichens, bryophytes and cyanobacteria on the soil surface—can buffer against the effects of warming and reduced rainfall on metallic nutrient availability. [ABSTRACT FROM AUTHOR]

Abstract Soil organic matter (SOM) protection, stability and long-term accumulation are controlled by several factors, including sorption onto mineral surfaces. Iron (Fe) has been suggested as a key regulator of SOM stability, both in acidic conditions, where Fe(III) is soluble, and in near-neutral pH environments, where it precipitates as Fe(III) (hydr)oxides. The present study aimed to probe, by sorption/desorption experiments in which Fe was added to the system, the mechanisms controlling Fe(III)-mediated organic carbon (C) stabilization; fine silt and clay (FSi + Cl) and fine sand (FSa) SOM fractions of three soils under different land uses were tested. Fe(III) addition caused a decrease in the organic C remaining in solution after reaction, indicating an Fe-mediated organic C stabilization effect. This effect was two times larger for FSa than for FSi + Cl, the former fraction being characterized by both low specific surface area and high organic C content. The organic C retained in the solid phase after Fe-mediated stabilization has relatively low sensitivity to desorption. Moreover, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy indicated that Fe-mediated organic C stabilization can be mainly ascribed to the formation of complexes between carbohydrate OH functional groups and Fe oxides. These results demonstrate that the binding of labile SOM compounds to Fe(III) contributes to its preservation, and that the mechanisms involved (flocculation vs. coating) depend on the size fractions. Graphical abstract Unlabelled Image Highlights • Fe(III) controls organic C stabilization in fine silt and clay and fine sand SOM fractions. • Fe(III) addition caused a decrease in the organic C in the solution. • The stabilization effect was larger for the fine sand SOM fraction. • The reaction with Fe(III) may promote either flocculation or coating phenomena. • The organic C retained after Fe-mediated stabilization has low sensitivity to desorption. [ABSTRACT FROM AUTHOR]

Biochar is a carbon (C)‐rich material produced from biomass by anoxic or oxygen‐limited thermal treatment known as pyrolysis. Despite substantial gaseous losses of C during pyrolysis, incorporating biochar in soil has been suggested as an effective long‐term option to sequester CO2 for climate change mitigation, due to the intrinsic stability of biochar C. However, no universally applicable approach that combines biochar quality and pyrolysis yield into an overall metric of C sequestration efficiency has been suggested yet. To ensure safe environmental use of biochar in agricultural soils, the International Biochar Initiative and the European Biochar Certificate have developed guidelines on biochar quality. In both guidelines, the hydrogen‐to‐organic C (H/Corg) ratio is an important quality criterion widely used as a proxy of biochar stability, which has been recognized also in the new EU regulation 2021/2088. Here, we evaluate the biochar C sequestration efficiency from published data that comply with the biochar quality criteria in the above guidelines, which may regulate future large‐scale field application in practice. The sequestration efficiency is calculated from the fraction of biochar C remaining in soil after 100 years (Fperm) and the C‐yield of various feedstocks pyrolyzed at different temperatures. Both parameters are expressed as a function of H/Corg. Combining these two metrics is relevant for assessing the mitigation potential of the biochar economy. We find that the C sequestration efficiency for stable biochar is in the range of 25%–50% of feedstock C. It depends on the type of feedstock and is in general a non‐linear function of H/Corg. We suggest that for plant‐based feedstock, biochar production that achieves H/Corg of 0.38–0.44, corresponding to pyrolysis temperatures of 500–550°C, is the most efficient in terms of soil carbon sequestration. Such biochars reveal an average sequestration efficiency of 41.4% (±4.5%) over 100 years. [ABSTRACT FROM AUTHOR]

Accumulating evidence suggests that warming associated with climate change is decreasing the total amount of soil organic carbon (SOC) in drylands, although scientific research has not given enough emphasis to particulate (POC) and mineral-associated organic carbon (MAOC) pools. Biocrusts are a major biotic feature of drylands and have large impacts on the C cycle, yet it is largely unknown whether they modulate the responses of POC and MAOC to climate change. Here, we assessed the effects of simulated climate change (control, reduced rainfall (RE), warming (WA), and RE + WA) and initial biocrust cover (low (< 20%) versus high (> 50%)) on the mineral protection of soil C and soil organic matter quality in a dryland ecosystem in central Spain for 9 years. At low initial biocrust cover levels, both WA and RE + WA increased SOC, especially POC but also MAOC, and promoted a higher contribution of carbohydrates, relative to aromatic compounds, to the POC fraction. These results suggest that the accumulation of soil C under warming treatments may be transitory in soils with low initial biocrust cover. In soils with high initial biocrust cover, climate change treatments did not affect SOC, neither POC nor MAOC fraction. Overall, our results indicate that biocrust communities modulate the negative effect of climate change on SOC, because no losses of soil C were observed with the climate manipulations under biocrusts. Future work should focus on determining the long-term persistence of the observed buffering effect by biocrust-forming lichens, as they are known to be negatively affected by warming. [ABSTRACT FROM AUTHOR]

Grazing represents the most extensive use of land worldwide. Yet its impacts on ecosystem services remain uncertain because pervasive interactions between grazing pressure, climate, soil properties, and biodiversity may occur but have never been addressed simultaneously. Using a standardized survey at 98 sites across six continents, we show that interactions between grazing pressure, climate, soil, and biodiversity are critical to explain the delivery of fundamental ecosystem services across drylands worldwide. Increasing grazing pressure reduced ecosystem service delivery in warmer and species-poor drylands, whereas positive effects of grazing were observed in colder and species-rich areas. Considering interactions between grazing and local abiotic and biotic factors is key for understanding the fate of dryland ecosystems under climate change and increasing human pressure. [ABSTRACT FROM AUTHOR]

Abstract: Intensive pig farming is a relevant economic activity in Mediterranean areas, which generates large amounts of pig slurry (PS) as a by-product. Pig slurry represents a valuable resource for low-fertility Mediterranean soils, capable of supplying organic matter and plant nutrients, particularly N. The cumulative and residual effects of PS on winter barley (Hordeum vulgare L.) yield and N use efficiency were investigated in a seven-year field experiment under semiarid Mediterranean conditions. Treatments included five rates of PS ranging from 30 to 150m3 ha−1 applied either every year or only once at the beginning of the experiment, an annual mineral N fertilization (traditional in the study area), and a control with no fertilization. Plant-available N content in soils after harvest increased with the annual application of PS with respect to the mineral fertilization and the control treatment, especially in dry years. Yearly variations in water availability also shaped the response of barley to PS fertilization. In general, the annual application of PS affected positively grain yield and biomass production. Residual effects were evident for the second and third barley crop. Cumulative N uptake by the barley crop increased with increasing the rate of PS (up to 120tha−1), while N use efficiency decreased, which suggested an increasing risk of leaching and contamination of ground water. As a whole, our data indicate that the annual application of 30m3 ha−1 of PS (equivalent to an average of 67kgNha−1) may result in barley yields similar to those obtained with the traditional mineral fertilization, while safely adhering to European regulations for the use of N in agriculture. The application of PS at rates higher than 60m3 ha−1 may result in better yields, but also in significantly lower N use efficiency and a higher potential environmental impact. [Copyright &y& Elsevier]

• Integral and profitable management of apple waste by hydrothermal carbonization. • Optical microscopy to evaluate successfully the transformation of biomass by HTC. • Solid by-products are CO 2 neutral fuels and show potential to enhance soil quality. • Liquid by-products contain valuable phenolic compounds and saturated fatty acids. • By-products properties are suited to final applications by selecting HTC conditions. Hydrothermal carbonization makes feasible the integral and profitable recovery of industrial apple waste within a zero-residue bio-economy. 82–96% of the energy and 80–93% of the C in the apple bagasse are retained in the solids generated by hydrothermal treatment at 180 and 230 °C for 2 and 4 h. Such processes stabilize the apple waste and lead to CO 2 neutral solid fuels with calorific value close to 30 MJ/kg. The agrochemical properties of the solid by-products suggest their potential to improve soil quality. Aqueous streams containing valuable phenolic compounds and saturated fatty acids are generated simultaneously, which provide additional cost-effectiveness. The by-products characteristics can be suited to the final application by selecting the reaction temperature, whereas the process duration has less impact. Optical microscopy and reflectance measurements are presented, for the first time, as powerful tools for assessing the biomass transformation when subjected to hydrothermal treatment under different conditions. [ABSTRACT FROM AUTHOR]

Abstract: Climate warming can result in both abiotic (e.g., permafrost thaw) and biotic (e.g., microbial functional genes) changes in Arctic tundra. Recent research has incorporated dynamic permafrost thaw in Earth system models (ESMs) and indicates that Arctic tundra could be a significant future carbon (C) source due to the enhanced decomposition of thawed deep soil C. However, warming‐induced biotic changes may influence biologically related parameters and the consequent projections in ESMs. How model parameters associated with biotic responses will change under warming and to what extent these changes affect projected C budgets have not been carefully examined. In this study, we synthesized six data sets over 5 years from a soil warming experiment at the Eight Mile Lake, Alaska, into the Terrestrial ECOsystem (TECO) model with a probabilistic inversion approach. The TECO model used multiple soil layers to track dynamics of thawed soil under different treatments. Our results show that warming increased light use efficiency of vegetation photosynthesis but decreased baseline (i.e., environment‐corrected) turnover rates of SOC in both the fast and slow pools in comparison with those under control. Moreover, the parameter changes generally amplified over time, suggesting processes of gradual physiological acclimation and functional gene shifts of both plants and microbes. The TECO model predicted that field warming from 2009 to 2013 resulted in cumulative C losses of 224 or 87 g/m2, respectively, without or with changes in those parameters. Thus, warming‐induced parameter changes reduced predicted soil C loss by 61%. Our study suggests that it is critical to incorporate biotic changes in ESMs to improve the model performance in predicting C dynamics in permafrost regions. [ABSTRACT FROM AUTHOR]