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9 páginas.- 5 figuras.- 51 referencias.- Supplementary information The online version contains supplementary material available at https://doi.org/10.1038/s41561-023-01170-x, Soil mosses are among the most widely distributed organisms on land. Experiments and observations suggest that they contribute to terrestrial soil biodiversity and function, yet their ecological contribution to soil has never been assessed globally under natural conditions. Here we conducted the most comprehensive global standardized field study to quantify how soil mosses influence 8 ecosystem services associated with 24 soil biodiversity and functional attributes across wide environmental gradients from all continents. We found that soil mosses are associated with greater carbon sequestration, pool sizes for key nutrients and organic matter decomposition rates but a lower proportion of soil-borne plant pathogens than unvegetated soils. Mosses are especially important for supporting multiple ecosystem services where vascular-plant cover is low. Globally, soil mosses potentially support 6.43 Gt more carbon in the soil layer than do bare soils. The amount of soil carbon associated with mosses is up to six times the annual global carbon emissions from any altered land use globally. The largest positive contribution of mosses to soils occurs under a high cover of mat and turf mosses, in less-productive ecosystems and on sandy and salty soils. Our results highlight the contribution of mosses to soil life and functions and the need to conserve these important organisms to support healthy soils., The study work associated with this paper was funded by a Large Research Grant from the British Ecological Society (no. LRB17\1019; MUSGONET). D.J.E. is supported by the Hermon Slade Foundation. M.D.-B. was supported by a Ramón y Cajal grant from the Spanish Ministry of Science and Innovation (RYC2018-025483-I), a project from the Spanish Ministry of Science and Innovation for the I + D + i (PID2020-115813RA-I00 funded by MCIN/AEI/10.13039/501100011033a) and a project PAIDI 2020 from the Junta de Andalucía (P20_00879). E.G. is supported by the European Research Council grant agreement 647038 (BIODESERT). M.B. is supported by a Ramón y Cajal grant from Spanish Ministry of Science (RYC2021-031797-I). A.d.l.R is supported by the AEI project PID2019-105469RB-C22. L.W. and Jianyong Wang are supported by the Program for Introducing Talents to Universities (B16011) and the Ministry of Education Innovation Team Development Plan (2013-373). The contributions of T.G. and T.U.N. were supported by the Research Program in Forest Biology, Ecology and Technology (P4-0107) and the research projects J4-3098 and J4-4547 of the Slovenian Research Agency. The contribution of P.B.R. was supported by the NSF Biological Integration Institutes grant DBI-2021898. J. Durán and A. Rodríguez acknowledge support from the FCT (2020.03670.CEECIND and SFRH/BDP/108913/2015, respectively), as well as from the MCTES, FSE, UE and the CFE (UIDB/04004/2021) research unit financed by FCT/MCTES through national funds (PIDDAC).

12 páginas.- 4 figuras.- 49 referencia.- Supplementary information The online version contains supplementary material available at https://doi.org/10.1038/s41558-023-01646-z .- Full-text access to a view-only version (Acceso a texto completo de sólo lectura en este enlace) https://rdcu.be/c8vZi, Urban greenspaces support multiple nature-based services, many of which depend on the amount of soil carbon (C). Yet, the environmental drivers of soil C and its sensitivity to warming are still poorly understood globally. Here we use soil samples from 56 paired urban greenspaces and natural ecosystems worldwide and combine soil C concentration and size fractionation measures with metagenomics and warming incubations. We show that surface soils in urban and natural ecosystems sustain similar C concentrations that follow comparable negative relationships with temperature. Plant productivity’s contribution to explaining soil C was higher in natural ecosystems, while in urban ecosystems, the soil microbial biomass had the greatest explanatory power. Moreover, the soil microbiome supported a faster C mineralization rate with experimental warming in urban greenspaces compared with natural ecosystems. Consequently, urban management strategies should consider the soil microbiome to maintain soil C and related ecosystem services., This study was supported by a 2019 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation (URBANFUN), and by BES Grant Agreement No. LRB17\1019 (MUSGONET). M.D-B., P.G-P., J.D. and A.R. acknowledge support from TED2021-130908B-C41/AEI/10.13039/501100011033/ Unión Europea NextGenerationEU/PRTR. M.D.-B. also acknowledges support from the Spanish Ministry of Science and Innovation for the I + D + i project PID2020-115813RA-I00 funded by MCIN/AEI/10.13039/501100011033. M.D.-B. was also supported by a project of the Fondo Europeo de Desarrollo Regional (FEDER) and the Consejería de Transformación Económica, Industria, Conocimiento y Universidades of the Junta de Andalucía (FEDER Andalucía 2014-2020 Objetivo temático ‘01 - Refuerzo de la investigación, el desarrollo tecnológico y la innovación’) associated with the research project P20_00879 (ANDABIOMA). D.J.E. was supported by the Hermon Slade Foundation. J.P.V. thanks the Science and Engineering Research Board (SERB) (EEQ/2021/001083, SIR/2022/000626) and the Department of Science and Technology (DST), India (DST/INT/SL/P-31/2021) and Banaras Hindu Univeristy-IoE (6031)-incentive grant for financial assistance for research in plant-microbe interaction and soil microbiome. J.D. and A. Rodríguez acknowledge support from the FCT (2020.03670.CEECIND and SFRH/BDP/108913/2015, respectively), as well as from the MCTES, FSE, UE and the CFE (UIDB/04004/2021) research unit financed by FCT/MCTES through national funds (PIDDAC).

22 páginas.-. 5 figuras.- 64 referencias.- Supplementary Information This pdf file includes: Supplementary Figs. 1–5, Tables 1–11 and references. https://static-content.springer.com/esm/art%3A10.1038%2Fs41559-022-01935-4/MediaObjects/41559_2022_1935_MOESM1_ESM.pdf, While the contribution of biodiversity to supporting multiple ecosystem functions is well established in natural ecosystems, the relationship of the above- and below-ground diversity with ecosystem multifunctionality remains virtually unknown in urban greenspaces. Here we conducted a standardized survey of urban greenspaces from 56 municipalities across six continents, aiming to investigate the relationships of plant and soil biodiversity (diversity of bacteria, fungi, protists and invertebrates, and metagenomics-based functional diversity) with 18 surrogates of ecosystem functions from nine ecosystem services. We found that soil biodiversity across biomes was significantly and positively correlated with multiple dimensions of ecosystem functions, and contributed to key ecosystem services such as microbially driven carbon pools, organic matter decomposition, plant productivity, nutrient cycling, water regulation, plant–soil mutualism, plant pathogen control and antibiotic resistance regulation. Plant diversity only indirectly influenced multifunctionality in urban greenspaces via changes in soil conditions that were associated with soil biodiversity. These findings were maintained after controlling for climate, spatial context, soil properties, vegetation and management practices. This study provides solid evidence that conserving soil biodiversity in urban greenspaces is key to supporting multiple dimensions of ecosystem functioning, which is critical for the sustainability of urban ecosystems and human wellbeing., This study was supported by a 2019 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation (URBANFUN), and by the BES grant agreement number LRB17\1019 (MUSGONET). M.D.-B. acknowledges support from the Spanish Ministry of Science and Innovation for the I+D+i project PID2020-115813RA-I00 funded by MCIN/AEI/10.13039/501100011033. M.D.-B. is also supported by a project of the Fondo Europeo de Desarrollo Regional (FEDER) and the Consejería de Transformación Económica, Industria, Conocimiento y Universidades of the Junta de Andalucía (FEDER Andalucía 2014-2020 Objetivo temático ‘01-Refuerzo de la investigación, el desarrollo tecnológico y la innovación’) associated with the research project P20_00879 (ANDABIOMA). H.C. was supported by the Strategic Priority Research Program of Chinese Academy of Sciences (XDA28020202), National Key R&D Program of China (2022YFD1500202) and the National Natural Science Foundation of China (91951109, 42230511, 92251305). K.F. was supported by Young Elite Scientist Sponsorship Program by CAST (2021QNRC001) and China Postdoctoral Science Foundation (2021M703302). F.D.A. and S.A. were supported by ANID FONDECYT 11180538 and 1170995. J.P.V. was supported by SERB (SIR/2022/000626, EEQ/2021/001083), DST (DST/INT/SL/P-31/2021) and Banaras Hindu University, IoE (6031) incentives grant for plant-microbe interaction and soil microbiome research. T.G. and T.U.N were supported by the Slovenian Research Agency grants P4-0107, J4-3098 and J4-4547.

We investigated the effects of biochar (BC) at 0 and 20 t ha-1, combined with two organic fertilizers (municipal solid waste compost, MC, and sewage sludge, SS), on soil organic matter (SOM) in a 9-year field experiment. To capture the protection by soil minerals and iron (Fe) against microbial decomposition, we fractionated SOM into particulate (POM) and mineral-associated organic matter (MAOM), and analyzed the fractions by iron (Fe) K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy.BC and the two organic amendments increased soil organic carbon (OC) content, but only the organic fertilizers significantly increased total nitrogen (N) content. BC increased particulate OC and total N contents, while the organic fertilizers only increased particulate total N content. BC significantly increased mineral-associated OC content, while the organic fertilizers increased both mineral-associated OC and total N contents. We found no interaction between BC and organic fertilizers on mineral-associated OC and total N contents. The Fe EXAFS data fitting showed that the Fe(III)-SOM content of the Fe phases in POM and MAOM in unamended soils were noticeably different. Hematite represented the main Fe oxide phase in the POM fractions from all the amended soils, and Fe(III)-SOM averaged around 15%. In the amended soils, besides hematite (also present in the unamended soil), ferrihydrite occurred in all MAOM fractions, although at a different proportion.

This study aims to investigate the mechanisms of soil organic carbon (SOC) sequestration with depth as a function of time and climate. Two chronosequences located along a climate gradient were investigated. The first chronosequence (ADI) consisted of fluvial terraces, whereas the second (LED) of fluvio-glacial terraces. Four sites (Q2, Q3, Q4 and Q5) located in 3 terraces (T1, T2, and T3), with age ranging from about 125,000 to 2,000 yr, were investigated for ADI, while 3 sites (Q1, Q2, and Q3) in 3 terraces (T1, T2, and T3, respectively), with age range from about 16,000 to 10,000 yr, were selected for LED. All sites were grasslands. Soil samples were collected (1 profile and 2 cores per site) by horizon, and each horizon sub-sampled by depth (each 5 cm). The sub-samples were characterized for pH, EC, total organic C, total N, texture, mineralogy, total and extractable elements, and for soil respiration. Particulate organic matter (POM) and mineral-associated organic matter (MAOM) were isolated and characterized by elemental and thermal analyses.In ADI, the oldest site (ADIQ2) stocks 2 times more C in the topsoil (15 cm) than the youngest site (ADIQ5) (60 and 27 MgC/ha, respectively). Furthermore, in ADIQ3, 38% of the total SOC accumulated between 30 and 80 cm (48 MgC/ha). In LED, the youngest site (LEDQ3) shows the highest SOC stock to both 15 and 30 cm (86 and 138 MgC/ha, respectively). In LEDQ1, 46% of the total SOC accumulated between 30 and 90 cm (94 MgC/ha). Among sites having same age but different climate, LEDQ3 (the wettest and coldest site) stocks ~2 times more carbon than ADIQ3 (the driest and warmest site) to the first 30 cm of depth.In LED, the ratio between the organic C in MAOM/POM in the topsoil ranges between 0.6 and 1.8, while in ADI between 1.1 and 3.9. Thermal indices (e.g., WL400-550/200-300, TG-T50) show that the stability of bulk SOM and pools generally increased with depth in ADI sites, whereas remained constant in LED. ADI soils had similar cumulative respiration (RHCUM), whereas LEDQ3 exhibited the highest RHCUM along the first 30 cm. Indeed, LEDQ3 had a 3× higher RHCUM than ADIQ3 in topsoil.Our data show that significant amounts of organic C were accumulated in deeper soils (>30cm). Moreover, soil organic matter (SOM) stability, and especially that of MAOM, in ADI increased with depth. The relative contribution of POM to C storage was more important in LED than in ADI, especially in the topsoil. Overall, our data suggest that climate has a greater influence on the size of SOC stocks than age, which in turn exerts a major influence on the stability of SOM.

11 páginas.- 4 figuras.- referencias.- Additional supporting information can be found online in the Supporting Information section at the end of this article., Soil micronutrients are capital for the delivery of ecosystem functioning and food provision worldwide. Yet, despite their importance, the global biogeography and ecological drivers of soil micronutrients remain virtually unknown, limiting our capacity to anticipate abrupt unexpected changes in soil micronutrients in the face of climate change. Here, we analyzed >1300 topsoil samples to examine the global distribution of six metallic micronutrients (Cu, Fe, Mn, Zn, Co and Ni) across all continents, climates and vegetation types. We found that warmer arid and tropical ecosystems, present in the least developed countries, sustain the lowest contents of multiple soil micronutrients. We further provide evidence that temperature increases may potentially result in abrupt and simultaneous reductions in the content of multiple soil micronutrients when a temperature threshold of 12–14°C is crossed, which may be occurring on 3% of the planet over the next century. Altogether, our findings provide fundamental understanding of the global distribution of soil micronutrients, with direct implications for the maintenance of ecosystem functioning, rangeland management and food production in the warmest and poorest regions of the planet., The sampling included in this study were supported by the European Research Council (ERC) grant 647038 (BIODESERT), the BES grant agreement No. LRB17\1019 (MUSGONET) and the Marie Skłodowska-Curie grant agreement 702057 (CLIMIFUN). We would like to thank the researchers originally involved in the BIODESERT, CLIMIFUN and MUSGONET projects for their help with samplings. E.M.-J. acknowledges the Humboldt Foundation for supporting his research stay in Germany (Fellowship for Experienced Researchers) and a project from the Spanish Ministry of Science and Innovation (PID2020-116578RB-I00). M.D.-B. is supported by a Ramón y Cajal grant (RYC2018-025483-I), a project from the Spanish Ministry of Science and Innovation (PID2020-115813RA-I00) and a project PAIDI 2020 from the Junta de Andalucía (P20_00879). E.G. is supported by the Conselleria de Innovación, Universidades, Ciencia y Sociedad Digital de la Generalitat Valenciana, and the European Social Fund grant APOSTD/2021/188 and European Research Council (ERC) grant 647038. F.T.M. is supported by European Research Council (ERC) grant 647038 and Generalitat Valenciana grant CIDEGENT/2018/041. M.D. and T.W.C. were funded by the Marc R. Benioff Revocable Trust and in collaboration with the World Economic Forum. This article is part of the contract between ETH Zurich and University of Alicante “Mapping terrestrial ecosystem structure at the global scale”. R.O.H. is supported by the Ramón y Cajal program from the MICINN (RYC-2017 22032), a PAIDI 2020 project from the Junta de Andalucía (Ref. 20_00323) and a project from the Spanish Ministry of Science and Innovation (PID2019-106004RA-I00/AEI/10.13039/501100011033). Authors acknowledge support by the Open Access Publication Initiative of Freie Universität Berlin. Open Access funding enabled and organized by Projekt DEAL.

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 ( 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. Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. This research has received funding from the European Research Council (ERC Grant agreement 647038 [BIODESERT]), the European Union’s Horizon 2020 research and innovation programme (Marie Skłodowska-Curie Grant Agreement No 654132 [VULCAN]), the Spanish Ministerio de Ciencia e Innovación (PID2020-116578RB-I00 [VULCOCLIM]) and Generalitat Valenciana (CIDEGENT/2018/041). P.D.-M. was supported by Spanish Ministerio de Ciencia, Innovación y Universidades (FPU17/02949), M. Panettieri acknowledge the financial support by the Comunidad de Madrid and the Spanish National Council of Scientific Researches research grant Atracción de Talento (grant number 2019T1/AMB14503).

The aim of this work is to investigate the mechanisms of soil organic carbon (SOC) sequestration as a function of time and depth. A chronosequence, consisting of two orders (T2 and T1) of the Adige river terraces (Veneto region, North of Italy) and 3 sites (Q2, Q3, and Q4), has been investigated. The highest and oldest terrace (T1) is located in Montalto di Gaium, 125 m above the current Adige riverbed level. This terrace was probably formed during the last interglacial (ca. 125,000 years BP) and was characterized by Paleudalf soils. Conversely, T2 represents the youngest order of terraces (probably formed during the early Holocene) and is situated 15 m above the current riverbed level. The Q2 site was located in T1 whereas Q3 and Q4 in T2; all sites have a common vegetation. From each site, soil samples have been collected (1 profile and 2 cores per site) by soil horizon, and each horizon sub-sampled by depth (each 5 cm). Five-cm thick sub-samples have been characterized for pH, electrical conductivity, total organic C (Corg), total N (NTOT), texture, and micro and macro nutrients. Particulate organic matter (POM) and mineral-associated organic matter (MAOM) have been isolated using a physical fractionation method and characterized by elemental (CHNS) and thermal analysis (TGA-DSC).The average Corg content in the topsoil (20 cm) is quite constant in the three sites (27.4 mg/g), whereas the average NTOT concentration ranges between 2.7 and 3.1 mg/g. In all sites, the Corg concentration along the profile is positively correlated with NTOT (porg and clay (porg sequestration. SOC stock in topsoil is 47% higher in Q2 (T1) (72±3 MgC/ha) than in Q4 (T2) (49±5 MgC/ha), but such a difference decreases at 35 cm (96±2 and 76±7 MgC/ha, respectively). Furthermore, in the site showing the deepest soil profile (Q3), the SOC accumulated between 35 and 80 cm (42 MgC/ha) represents the 33% of the total. The average content of the MAOM pool is constant along the T2 (Q3 and Q4) profiles (52%), while increases with depth in T1 (up to 62% in deeper layers).Thermal indices (e.g., WL400-550/200-300, TG-T50, DSC-T50) suggest that the stability of bulk SOM generally increases with depth in the three sites. Moreover, a general increase in the thermal stability of both MAOM and POM is observed with depth in all sites, with Q2 (i.e., the site in the oldest terrace) showing a larger increase of MAOM thermal stability in deeper soil compared to Q3 and Q4 (located on the youngest terrace).While most of the studies on SOC sequestration and stabilization focuses on topsoils, our preliminary data show that a significant stock of more recalcitrant organic C accumulates in deeper soils. Future data will help to better understand the effect of time on SOC distribution among different pools and as a function of depth.

Dryland soils provide different societal and environmental services, such as food supply and biodiversity support. In Europe, most of the dryland areas are devoted to agriculture. In the next decades, both European and worldwide drylands are expected to suffer with increased intensity due to the expected climate change-derived rise in aridity. Many studies have focussed on aridity-induced changes in major nutrients in drylands, but little is known of the impact of environmental and biogeochemical factors on micronutrients with critical roles in life, and as inorganic contaminants with ecotoxicological implications. We analysed and explored drivers of total and available concentrations of micronutrients (Co, Cu, Fe, Mo, Mn, Ni and Zn) and contaminants (As, Cd and Pb) in 148 soil samples collected from European drylands covering a wide range of aridity and of other geochemical parameters. The availability of micronutrients increased with their total content, decreased with pH and was enhanced by organic C content. Aridity decreased the availability of Fe, a key element in human diet. Our findings also highlight the scarcity of this micronutrient in European drylands, as well as of some other important micronutrients like Zn and Mo in agricultural soils. Total content was the main driver of the availability of Cd and Pb, and organic matter exerted synergistic effects on contaminant release. Our data show the need for precise management practices to be incentivised by agricultural and environmental policies in order to ensure micronutrient supply and avoid contamination, thus maintaining adequate levels of agricultural productivity and simultaneously preserving dryland ecosystems. Highlights: Drylands are important for food production in Europe and sensitive to climate change. The occurrence of metals in European Union dry soils and the drivers influencing them were studied. Some micronutrients (Fe, Mo and Zn) were scarce while contaminants were abundant. SOC, pH and clays were the main drivers of element availability; aridity reduced Fe. Agricultural practises are needed to ensure nutrient supply and prevent contamination., This work was funded by a 2018 Leonardo Grant for Researchers and Cultural Creators of the Fundación BBVA (Spain).

Biochar aging may affect the interactions of biochar with water and thus its performance as soil amendment; yet the specific mechanisms underlying these effects are poorly understood. By means of FTIR, N adsorption, Hg intrusion porosimetry, thermogravimetric analysis, C solid state nuclear magnetic resonance (NMR) and H NMR relaxometry, we investigated changes in the chemistry and structure of biochar as well as its interaction with water after biochar aging, both physical (simulated by ball-milling) and biochemical (simulated by co-composting). Three different porosities of biochar were examined, This study was financially supported by the Comunidad de Madrid (Spain) and the Spanish National Research Council (CSIC) research grant Atracci ́on de Talento [grant number 2019T1/AMB14503]. The authors acknowledge the funding received from the Spanish National Research Council and the French National Centre for Scientific Research through the cooperation projects PICS [grant number 018FR0044] and IEA (ex-PICS) [grant number 203026]. This work was also partially funded by the Spanish Ministerio de Ciencia e Innovaci ́on (PTA 2018- 015282-I and PID 2020-119047RB-I00) and Comunidad de Madrid (PEJ-2018-TL/IND-11075). The authors want to thank the analytical services for the 1H relaxometry NMR at ICTP-CSIC, for the solid state 13C NMR at IRNAS-CSIC and for FT-IR, TGA and porosimetry analyses at ICA-CSIC. Technical support provided by Mr. H ́ector Fritis, Ms. Cristina G ́omez Ruano, Mr. David Mabilais, Mr. Fernando Martín Salamanca and Dr. Rebeca Herrero is gratefully acknowledged.

19 páginas.- 5 figuras.- 98 referencias.- Supplementary information The online version contains supplementary material available at https://doi.org/10.1038/s41586-022-05292-x, Soils are the foundation of all terrestrial ecosystems1. However, unlike for plants and animals, a global assessment of hotspots for soil nature conservation is still lacking2. This hampers our ability to establish nature conservation priorities for the multiple dimensions that support the soil system: from soil biodiversity to ecosystem services. Here, to identify global hotspots for soil nature conservation, we performed a global field survey that includes observations of biodiversity (archaea, bacteria, fungi, protists and invertebrates) and functions (critical for six ecosystem services) in 615 composite samples of topsoil from a standardized survey in all continents. We found that each of the different ecological dimensions of soils—that is, species richness (alpha diversity, measured as amplicon sequence variants), community dissimilarity and ecosystem services—peaked in contrasting regions of the planet, and were associated with different environmental factors. Temperate ecosystems showed the highest species richness, whereas community dissimilarity peaked in the tropics, and colder high-latitudinal ecosystems were identified as hotspots of ecosystem services. These findings highlight the complexities that are involved in simultaneously protecting multiple ecological dimensions of soil. We further show that most of these hotspots are not adequately covered by protected areas (more than 70%), and are vulnerable in the context of several scenarios of global change. Our global estimation of priorities for soil nature conservation highlights the importance of accounting for the multidimensionality of soil biodiversity and ecosystem services to conserve soils for future generations., This project received funding from the British Ecological Society (agreement LRA17\1193; MUSGONET). C.A.G. and N.E. were funded by DFG–FZT 118, 202548816; C.A.G. was supported by FCT-PTDC/BIA-CBI/2340/2020; M.D.-B. was supported by RYC2018-025483-I, PID2020-115813RA-I00\MCIN/AEI/10.13039/501100011033 and P20_00879. M.A.M.-M. and S.A. were funded by FONDECYT 1181034 and ANID-PIA-Anillo INACH ACT192057. J.D. and A.R. acknowledge support from IF/00950/2014, 2020.03670.CEECIND, SFRH/BDP/108913/2015 and UIDB/04004/2020. Y.-R.L. was supported by 2662019PY010 from the FRFCU. L.T. was supported by the ESF grant PRG632. F.B. and J.L.M. were supported by i-LINK+2018 (LINKA20069) funded by CSIC. C.T.-D. was supported by the Grupo de Biodibersidad & Cambio Global UBB–GI 170509/EF. C.P. was supported by the EU H2020 grant agreement 101000224. H.C. was supported by NSFC32101335, FRFCU2412021QD014 and CPSF2021M690589. J.P.V. was supported by DST (DST/INT/SL/P-31/2021) SERB (EEQ/2021/001083) and BHU-IoE (6031).

The rapid spread of invasive Pampas grass (PG) is having not only ecosystems impact, but also significant economic and social effects. The tonnes of bulky waste from the plant disposal require proper treatment to avoid seed dispersal, greenhouse gas emissions and landscape damage. In the pursuit of zero-waste management, hydrothermal treatment (HT) appears as a challenging alternative. The possibility of mobile HT systems offers an alternative to accomplish on-site both the PG waste management and the application of the resulting by-products within a circular framework. As a first step, this research shows that, without a prior drying step, the hydrothermal treatment at 100-230 °C under autogenous water vapor pressure for only 30 min allows safe seeds inertization, while a stable carbon-enriched solid and an aqueous stream are generated. Prolonging the process for 2 h has no profitable effects. As the reaction temperature increases, the PG residue is converted into a material with 49–58 wt% of carbon, 41–32 wt% of oxygen and 3–4 wt% of ash. The pH (~6.3), low electrical conductivity (1.21–0.86 dS/m), high carbon content, open porosity (5–8 m2/g) and improved performance in seed germination and in the early growth test suggest the potential of HT-solids derived at 100–120 °C as amendment to sequester carbon in the soil and improve its physico-biological properties. The phytotoxicity detected in the peat/lignite-like solids obtained at 200–230 °C limits its application in soil, but calorific values of 22–24 MJ/kg indicate their suitability as CO2-neutral fuel. The agrochemical analysis of the liquid by-products indicates poor value on their own, but their use supplemented with compost may be an option., The authors gratefully acknowledge the funds provided by Consejería de Infraestructuras, Ordenación del Territorio y Medio Ambiente (Dirección General de Biodiversidad)-Principality of Asturias- Spain (grant 18.07-443F-703.011). The seeds germination tests were carried out with the support of the project LIFE Stop Cortaderia (LIFE17 NAT/ES/000495). The support provided by COGERSA SAU is highly acknowledged.

The structure and function of the soil microbiome of urban greenspaces remain largely undetermined. We conducted a global field survey in urban greenspaces and neighboring natural ecosystems across 56 cities from six continents, and found that urban soils are important hotspots for soil bacterial, protist and functional gene diversity, but support highly homogenized microbial communities worldwide. Urban greenspaces had a greater proportion of fast-growing bacteria, algae, amoebae, and fungal pathogens, but a lower proportion of ectomycorrhizal fungi than natural ecosystems. These urban ecosystems also showed higher proportions of genes associated with human pathogens, greenhouse gas emissions, faster nutrient cycling, and more intense abiotic stress than natural environments. City affluence, management practices, and climate were fundamental drivers of urban soil communities. Our work paves the way toward a more comprehensive global-scale perspective on urban greenspaces, which is integral to managing the health of these ecosystems and the well-being of human populations., M.D.-B. and this project were supported by a 2019 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation (URBANFUN) and by the BES grant agreement no. LRB17\1019 (MUSGONET). M.D.-B. is also supported by a Ramón y Cajal grant from the Spanish Ministry of Science and Innovation (RYC2018-025483-I). N.F. was supported by grants from the U.S. National Science Foundation (DEB1556090 and DEB1542653). L.T. acknowledges support from Norway-Baltic collaboration grant EMP442 and Estonian Science Foundation grant PRG632. B.K.S. acknowledges a research award by the Humboldt Foundation and funding from the Australian Research Council (DP190103714). F.A. is supported by ANID FONDECYT 11180538 and 1170995. S.A. is funded by ANID FONDECYT 1170995 and ANID ANILLO ACT192027. F.B. and J.L.M. acknowledge support from the Spanish Ministry and FEDER funds for the project AGL2017-85755-R, the i-LINK+ 2018 (LINKA20069) from CSIC, as well as funds from “Fundación Séneca” from Murcia Province (19896/GERM/15). C.P. acknowledges support from the Spanish State Plan for Scientific and Technical Research and Innovation (2013–2016), award reference AGL2016-75762-R (AEI/FEDER, UE). M.B. acknowledges support from a Juan de la Cierva Formación grant from the Spanish Ministry of Economy and Competitiveness (FJCI-2018-036520-I). T.P.M. would like to acknowledge contributions from the National Research Foundation of South Africa and cities involved in the South African survey. Slovenian coauthors were supported by the research project J4-1766 “Methodology approaches in genome-based diversity and ecological plasticity study of truffles from their natural distribution areas” and the Research Program in Forest Biology, Ecology, and Technology (P4-0107) of the Slovenian Research Agency. J.D. and A. Rey acknowledge support from the FCT (IF/00950/2014 and SFRH/BDP/108913/2015, respectively), as well as from the MCTES, FSE, UE, and the CFE (UIDB/04004/2020) research unit financed by FCT/MCTES through national funds (PIDDAC). J.P.V. acknowledges financial support from SERB (Science and Engineering Research Board) (EEQ/2017/000775) India. J.-Z.H. and H.-W.H. are financially supported by Australian Research Council (DP170101628).

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.

Evidence suggests that 5–15% of the vast pool of soil carbon stored in northern permafrost ecosystems could be emitted as greenhouse gases by 2100 under the current path of global warming. However, direct measurements of changes in soil carbon remain scarce, largely because ground subsidence that occurs as the permafrost soils begin to thaw confounds the traditional quantification of carbon pools based on fixed depths or soil horizons. This issue is overcome when carbon is quantified in relation to a fixed ash content, which uses the relatively stable mineral component of soil as a metric for pool comparisons through time. We applied this approach to directly measure soil carbon pool changes over five years in experimentally warmed and ambient tundra ecosystems at a site in Alaska where permafrost is degrading due to climate change. We show a loss of soil carbon of 5.4% per year (95% confidence interval: 1.0, 9.5) across the site. Our results point to lateral hydrological export as a potential pathway for these surprisingly large losses. This research highlights the potential to make repeat soil carbon pool measurements at sentinel sites across the permafrost region, as this feedback to climate change may be occurring faster than previously thought. Permafrost loses carbon at a faster rate than previously thought as climate warms, according to direct soil carbon observations over five years in the field in Alaska’s tundra ecosystem.

The application of biochar is presumed to be a climate change mitigation strategy in agriculture. However, we still need to better understand the effects of biochar application on soil properties, particularly on soil microbial activity. This is because soil microorganisms play a key role in ecosystems functioning, as they have a central role in soil metabolic activity given that they are responsible for soil organic matter decomposition and nutrient cycling. Conversely, little is known about how climate change will affect the soil microbial activity.In a rainfed field experiment, we studied the effect of forecasted warming and rainfall reduction on soil respiration and soil enzymatic activities after 3 years of consecutive application of biochar at a rate of 20 t/ha on a barley-camelina-fallow rotation in a semiarid region in Central Spain. Soil respiration was not affected by the application of biochar or/and warming and rainfall reduction treatments in comparison to the control treatment (no amendment). However, biochar amended soils had lower temperature sensitivity of soil C mineralization in the first two years when soils were cultivated but higher temperature sensitivity of soil C mineralization in the third year during fallow treatment. Enzymes involved in the C and N cycles (dehydrogenase, β-glucosidase and urease) significantly increased their activity under warming and rainfall reduction treatments, albeit biochar application tended to decrease the enzymatic activity under those treatments.Acknowledgments: to the Spanish MICINN (MINECO, AEI, FEDER, EU) for supporting the research projects AGL2016-75762-R and CGL2015-65162-R.

BACKGROUND: Nowadays a significant amount of land contaminated with toxic elements is being used for agriculture, posing a serious risk of crop contamination and toxicity. Several methodologies are being used to remediate soil contamination, including the use of amendments such as biochar. This work evaluated the effects of biochar combined with different fertirrigations (water, a conventional fertilizer solution, or a fertilizer solution with a commercial biostimulant derived from leonardite) on the availability of toxic elements and nutrients for pepper cultivated in a soil contaminated with As, Cd, Pb, and Zn. RESULTS: Irrigation with fertilizer solutions improved plant growth regardless of the biochar amendment. Biochar decreased the bioavailability of Cu and Pb in soil and the Cu content in pepper leaves. Combined with fertilization, biochar also decreased plant As and Pb content. Biochar combined with biostimulant decreased the bioavailable content of Cd in soil and its uptake by pepper plants. CONCLUSION: The use of biochar and biostimulant presented advantages for plant production in a non-suitable scenario of nutrient scarcity and contamination, We thank the agronomic technicians Manuel Campos Macossay and Carlos Rodriguez Orta for the location of the soil and supply of materials. This article is the result of a research project ‘Compar ison of agronomic efficiency between Huma Gro® products and mineral conventional fertilizers’ funded by Bio Huma Netics Inc. (Gilbert, Arizona, USA). Bio Huma Netics Inc. did not participate in the experimental procedures or in the evaluation of the results

Soil microbes, and the proteins they produce, are responsible for a myriad of soil processes which are integral to life on Earth, supporting soil fertility, nutrient fluxes, trace gas emissions, and plant production. However, how and why the composition of soil microbial proteins (the metaproteome) changes across wide gradients of vegetation, climatic and edaphic conditions remains largely undetermined. By applying high-resolution mass spectrometry to soil samples collected from four continents, we identified the most common proteins in soils, and investigated the primary environmental factors driving their distributions across climate and vegetation types. We found that soil proteins involved in carbohydrate metabolism, DNA repair, lipid metabolism, transcription regulation, tricarboxylic acid cycling, nitrogen (N) fixation and one-carbon metabolism dominate soils across a wide range of climates, vegetation types and edaphic conditions. Vegetation type and climate were important factors determining the community composition of the topsoil metaproteome. Moreover, we show that vegetation type, climate, and key edaphic proporties (mainly soil C fractions, pH and texture) influenced the proportion of important proteins involved in biogeochemical cycles and cellular processes. We also found that protein-based taxonomic information based on proteins has a greater resolution than 16S rRNA gene sequencing with regards to the ability to detect significant correlations with environmental variables. Together, our work identifies the dominant proteins produced by microbes living in a wide range of soils, and advances our understanding of how environmental changes can influence the structure and function of the topsoil metaproteome and the soil processes that they support.

Author(s): Rodenhizer, Heidi; Ledman, Justin; Mauritz, Marguerite; Natali, Susan M; Pegoraro, Elaine; Plaza, Cesar; Romano, Emily; Schadel, Christina; Taylor, Meghan; Schuur, Edward

The biogeochemical cycling of multiple soil elements is fundamental for life on Earth. Here, we conducted a global field survey across 16 chronosequences from contrasting biomes with soil ages ranging from centuries to millions of years. For this, we collected and analysed 435 topsoil samples (0-10 cm) from 87 locations. We showed that high levels of topsoil element coupling, defined as the average correlation among nineteen soil elements, are maintained over geological timescales globally. Cross-biome changes in plant biodiversity, soil microbial structure, weathering, soil pH and texture, and mineral-free unprotected organic matter content largely controlled multi-element coupling. Moreover, elements with heavier atomic mass were naturally more decoupled and unpredictable in space than those with lighter mass. Only the coupling of carbon, nitrogen and phosphorus, which are essential to life on Earth, deviated from this predictable pattern, suggesting that this anomaly may be an undeniable fingerprint of life in terrestrial soils.

Redox-driven changes in Fe crystallinity and speciation may affect soil organic matter (SOM) stabilization and carbon (C) turnover, with consequent influence on global terrestrial soil organic carbon (SOC) cycling. Under reducing conditions, increasing concentrations of Fe(II) released in solution from the reductive dissolution of Fe (hydr)oxides may accelerate ferrihydrite transformation, although our understanding of the influence of SOM on these transformations is still lacking. Here, we evaluated abiotic Fe(II)-catalyzed mineralogical changes in Fe (hydr)oxides in bulk soils and size-fractionated SOM pools (for comparison, fine silt plus clay, FSi+Cl, and fine sand, FSa) of an agricultural soil, unamended or amended with biochar, municipal solid waste compost, and a combination of both. FSa fractions showed the most significant Fe(II)-catalyzed ferrihydrite transformations with the consequent production of well-ordered Fe oxides irrespective of soil amendment, with the only exception being the compost-amended soils. In contrast, poorly crystalline ferrihydrite still constituted ca. 45% of the FSi+Cl fractions of amended soils, confirming the that the higher SOM content in this fraction inhibits atom exchange between aqueous Fe(II) and the solid phase. Building on our knowledge of Fe(II)-catalyzed mineralogical changes in simple systems, our results evidenced that the mechanisms of abiotic Fe mineral transformations in bulk soils depend on Fe mineralogy, organic C content and quality, and organo-mineral associations that exist across particle-size SOM pools. Our results underline that in the fine fractions the increase in SOM due to organic amendments can contribute to limiting abiotic Fe(II)-catalyzed ferrihydrite transformation, while coarser particle-size fractions represent an understudied pool of SOM subjected to Fe mineral transformations.

In a previous study (Zaccone et al., 2018. Appl. Soil Ecol. 130, 134-142), we evaluated the potential ecological partition of microbial and plant DNA across soil organic matter (SOM) fractions linked to conceptual stabilization mechanisms. We found that different microbial taxa (bacterial and fungal) seem to be specifically associated to SOM fractions. In the present work we investigated the short-term distribution of exogenous microbial population in SOM fractions following inoculation, in order to track the fate of bacterial DNA (in the form of spores) artificially spiked in bulk soils. The main hypothesis was that the colonization of external organisms proceeds from the unprotected fraction (FR) towards those protected physically and/or chemically by soil minerals from decomposition (i.e., into macro and micro-aggregates [MA, MI] or interacting with mineral surfaces [MIN]).Three different soils with different pH, SOM content and texture were used in the experiment. One aliquot of soil was spiked with approx. 8 Log cfu of spore of Bacillus clausii from a commercial preparation of 4 strains. DNA was extracted from soil and recovered from SOM pools isolated using a physical fractionation method [Plaza et al., 2012. CLEAN-Soil Air Water 40, 134-139] and quantified by fluorescence (Qubit).DNA recovered from spiked vs. non-spiked samples followed two different patterns of distribution, according to the SOM fractions. Total DNA in the bulk soils varied according to the soil types and the effect of spiking 8 cfu was negligible. In the SOM fractions, while MI and MIN showed different concentration according to the soil type (no apparent influence of spiking), total DNA in FR was clearly higher for spiked samples, while MA had a putative interaction between soil type and spiking. Even if very preliminary, our results point out a possible mechanism of short-term distribution of exogenous DNA (through spores and potential vegetative forms of B. clausii germinated during the incubation) from the free SOM to the macroaggregates, with no apparent influence on MI and MIN yet.Further analyses (e.g., PCR-ARISA and qPCR) will allow to disclose whether indigenous vs. exogenous bacterial DNA are differentially distributed in SOM, possibly enhancing the description of the mechanisms underlying the distribution of microbial communities in soil, according to the different organization of the SOM in soil aggregates.

The role and distribution of iron (Fe) species in physical soil fractions have received remarkably little attention in field-scale systems. Here, we identify and quantify the Fe phases into two fractions (fine sand, FSa, and fine silt and clay, FSi + Cl), isolated from an agricultural soil unamended and amended with different organic materials, by Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The linear combination fitting and wavelet transform of EXAFS data revealed noticeable differences between unamended FSa and FSi + Cl fractions. Specifically, the FSi + Cl fraction was mainly characterized by ferrihydrite (48%) and Fe(III)-soil organic matter (SOM) complexes (37%), whereas in the FSa fraction, ferrihydrite still represented a major phase (44%), with a lower contribution from Fe(III)-SOM (18%). In the FSa fraction, the addition of the organic amendments resulted in an increase of Fe-SOM complexes (31-35%) and a decrease of ferrihydrite (28-29%). By contrast, in the amended FSi + Cl fractions, the added organic matter led to negligible changes in percent ferrihydrite. Therefore, regardless of the amendment type, the addition of organic matter to soil increased the capability of the coarse fraction (FSa) to stabilize organic carbon, thus pointing out that the role of FSa in carbon sequestration in agricultural soils at a global scale may be overlooked.

Biochar application is now considered to be one of the most promising agricultural practices to mitigate climate change. However, to fully assess the benefits of biochar, we still need to better understand its effects on soil properties, and particularly on native soil organic matter (SOM) dynamics.In this work, we investigated soil respiration and changes in SOM pools (mineral-free, intra-aggregate, and mineral-associated SOM) as affected by the application of 20 t / ha per year of biochar alone or combined with mineral fertilizer, municipal solid waste compost, or sewage sludge. The experiment was run for 7 years in a semiarid agricultural soil. We found that biochar had no effect on soil respiration with respect to mineral fertilization and no amendment (control), and tended to decrease CO2 emissions from soils amended with municipal solid waste compost and sewage sludge. Biochar accumulated mainly in the mineral-free SOM fraction and its addition, especially in combination with municipal solid waste compost, promoted the amount of SOM occluded with aggregates and associated to mineral surfaces.Acknowledgments: to the Spanish MICINN (MINECO, AEI, FEDER, EU) for supporting the research project AGL2016-75762-R.

The Fe(II)-catalyzed transformation of ferrihydrite into highly crystalline forms may represent an important pathway for soil organic matter (SOM) destabilization under moderately reducing conditions. However, the link between redox-driven changes in soil Fe mineral composition and crystallinity and SOM chemical properties in the field remains elusive. We evaluated abiotic Fe(II)-catalyzed mineralogical transformation of Fe (oxyhydr)oxides in bulk soils and two particle-size SOM fractions, namely the fine silt plus clay (

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.

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., This project received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant Agreement No. 702057 (CLIMIFUN). M.D.-B. is supported by a Ramón y Cajal grant from the Spanish Ministry of Science and Innovation (RYC2018-025483-I), and by the BES Grant Agreement No. LRB17\1019 (MUSGONET). F.B. is grateful to the Spanish Ministry and FEDER funds for the project AGL2017–85755-R, the i-LINK+2018 (LINKA20069) from CSIC, and received funds from “Fundación Séneca” from Murcia Province (19896/GERM/15). S.R. was supported by the US Geological Survey Ecosystems Mission Area. C.P. acknowledges support from the Spanish State Plan for Scientific and Technical Research and Innovation (2013–2016), award ref. AGL201675762-R (AEI/FEDER, UE). A.G. acknowledges support from the Spanish Ministry of Science (CGL2017-88124-R). F.A. is supported by FONDECYT 11180538 and S.A. by FONDECYT 1170995. We would like to thank Peter Vitousek for his comments on a previous draft of this paper. Moreover, we thank Matt Gebert, Jessica Henley, Fernando T. Maestre, Victoria Ochoa, and Beatriz Gozalo for their help with lab analyses, and Emilio Guirado for his advice with topographic analyses. We also want to thank Osvaldo Sala, Matthew A. Bowker, Peter Vitousek, Courtney Currier, Martin Kirchmair, Victor M. Peña-Ramírez, Lynn Riedel, Julie Larson, Katy Waechter, David Buckner, and Brian Anacker for their help with soil sampling, and to the City of Boulder Open Space and Mountain Parks for allowing us to conduct these samplings. We are also grateful to the Division of Forestry and Wildlife of the State of Hawai’i and Koke’e State Park for their logistical assistance and for allowing us access to the HA sites. The Arizona research sites were established with the support of an EPA‐STAR Graduate Fellowship (U‐916251), a Merriam‐Powell Center for Environmental Research Graduate Fellowship, an Achievement Rewards for College Scientists (ARCS) Foundation of Arizona Scholarship, and McIntire‐Stennis appropriations to Northern Arizona University and the State of Arizona. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Iron (Fe) speciation in soils is highly dependent on environmental conditions, mineralogy, and chemical interactions with soil organic matter (SOM). The fine silt and clay (FSi + Cl) particle size fraction of soils constitutes a primary organo-mineral fraction and contains SOM with long turnover time. In this study, the FSi + Cl particle size fractions isolated from a coniferous forest, a grassland, a technosol, and an agricultural soil were reacted with Fe(III) at pH 7. Unreacted and reacted samples were then investigated by means of extended X-ray absorption fine structure (EXAFS) spectroscopy. Statistical methods were used to determine goodness-of-fit parameters for linear combination fitting (LCF) and wavelet transformation (WT) of the Fe K-edge EXAFS data. WT separated spectral contributions from different backscattering atoms in higher coordination shells located at similar interatomic distances from the central absorbing Fe atom. LCF results paired with WT showed that the FSi + Cl particle size fractions consisted of a mixture of Fe phyllosilicates, Fe (hydr)oxides, and organically complexed Fe in different proportions. Our research revealed that after sorption experiments, in which Fe(III) was added to the system, increasing amounts of Fe(III)-SOM complexes were found in the solid phase of grassland and agricultural soils, whereas the precipitation of Fe(III) led to the preferential formation of ferrihydrite in the coniferous forest soil and in the technosol. Although the quantitative Fe-mediated organic carbon stabilization effect after Fe(III) addition is shown in this work, Fe speciation is not clearly related to SOM amount or quality (i.e., carbon-to-nitrogen ratio). The variation of Fe chemical speciation among the soil fractions likely translates into differences in their environmental fate.

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 CO2 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., The funding from the European Regional Development Fund (ERDF) through project CEMOWAS2 (SOE2/P5/F0505)-INTERREG V SUDOE 2017 and Plan de Ciencia, Tecnología e Innovación (PCTI) 2018–2020 del Principado de Asturias and ERDF through project IDI/2018/000233 is acknowledged. The authors also acknowledge support from the Spanish State Plan for Scientific and Technical Research and Innovation (2013-2016), ref. AGL201675762-R. This study was partly supported by grant AGL2016-76832-R from the National Program for Research Aimed at the Challenges of Society (Spain).

Changing climatic conditions (warming and decreasing precipitation) have been found to be a threat to the agricultural sustainability of Mediterranean croplands. From the climate change perspective, biochar amendment may interact with the effects of warming and drought stresses on soil ecosystems. However, the responses of soil microbial communities to the joint effects of climate change and biochar in Mediterranean croplands are not sufficiently known. To help fill this knowledge gap, in this work we used a field experiment to determine the effects of partial rain exclusion alone or combined with a soil temperature increase in biochar-amended (20 t ha) and unamended plots under crop rotation on soil chemical properties, enzyme activities, and the microbial community activity, structure, composition, abundance, and functions. The biomass, composition, and activity of the soil bacterial and fungal communities were more responsive to biochar addition than to climate manipulation. Thus, soil chemical parameters, enzyme activities and the relative abundances of bacterial populations were not responsive to the interaction of biochar and climate manipulation, while the predicted functionality of the bacterial community was modified by both factors. Soil β-glucosidase activity significantly decreased in response to biochar addition and climate manipulation, while urease activity was significantly increased by biochar, and protease activity was significantly decreased by climate manipulation. Gram negative and fungal biomasses were significantly affected by the interaction of biochar with climate manipulation. Climate manipulation produced changes in the composition of the soil fungal community without loss of diversity. This study illustrates how the interactions between biochar amendment and future climate change scenarios influence microbially-driven ecosystem services related to the maintenance of nutrient cycles and biodiversity in a Mediterranean agroecosystem., This research was financially supported by the Spanish MICINN MINECO, AEI, FEDER, EU), through the research projects CGL2015-65162-R and AGL2016-75752-R. The authors are also grateful for the AEPP CSIC funds (2020AEP004). We also thank the Spanish Ministry and FEDER funds for the project AGL2017–85755-R (AEI/FEDER, UE), the i-LINK + 2018 (LINKA20069) from CSIC.

The persistence of soil organic matter (SOM) constituents as a function of their recalcitrance has been recently questioned, with several papers showing the influence of the combined action of physical protection and chemical stabilization mechanisms as the main factors affecting SOM mean residence time. Using a physical fractionation method, SOM located between aggregates (FR), occluded within macro- (MA) and micro-aggregates (MI), and associated with the mineral fractions (MIN) were isolated from an agricultural soil differently amended (using compost, sewage sludge and biochar), and the occurrence of (total, bacterial and plant) DNA in these SOM pools was investigated. Following physical fractionation, total DNA (tDNA) was recovered from all SOM pools and from all treatments. Independently from the amendment, most tDNA accumulates in the FR fraction (30–70%), followed by the MIN pool (25–55%). The positive correlation between tDNA contents and C/N ratios (both tending to decrease following the order FR, MA and MI) observed for the light SOM fractions, together with the opposite pattern characterizing the heavy, MIN fraction (characterized by relatively high tDNA contents and low C/N ratios), suggests a different origin of the latter SOM pool, i.e., new molecules resulting from microbial transformations rather than highly degraded litter inputs. Therefore, tDNA may represent a promising proxy of organic matter dynamics in mineral soils. Finally, the MI fraction shows the highest number of microbial taxa and diversity, and seems to constitute a separate microbial niche in which different bacterial communities carry out their activity.

Accrual of carbon (C) and nitrogen (N) in soil is a significant and realizable management option to mitigate climate change; thus, a clear understanding of the mechanisms controlling the persistence of C and N in soil organic matter (SOM) across different ecosystems has never been more needed. Here, we investigated SOM distribution between physically and chemically stabilized fractions in soils from a variety of ecosystems (i.e., coniferous and broadleaved forest soils, grassland soils, technosols, and agricultural soils). Using elemental and thermal analyses, we examined changes in the quantity and quality of physically fractionated SOM pools characterized by different mechanisms of protection from decomposition. Independently of the ecosystem type, most of the organic C and total N were found in the mineral-associated SOM pool, known to be protected mainly by chemical mechanisms. Indexes of thermal stability and C/N ratio of this heavy SOM fraction were lower (especially in agricultural soils) compared to light SOM fractions found free or occluded in aggregates, and suggested a marked presence of inherently labile compounds. Our results confirm that the association of labile organic molecules with soil minerals is a major stabilization mechanism of SOM, and demonstrate that this is a generalizable finding occurring across different mineral soils and ecosystems.

Peat is the most widely used substrate component and extensively used in greenhouse cultivation, landfill cover soils, urban parks and gardens, urban agriculture or green roofs, due to its excellent combination of physicochemical properties. The production of hydrochar by hydrothermal carbonization (a process at lower temperatures than pyrolysis and using wet conditions) could industrially reproduce the initial conditions of biomass humification and lead to materials with similar properties to those of peat. The objective of this work was to compare peat (PT, Control), a hydrochar prepared from biosolids (HSL), a hydrochar prepared from the organic fraction of urban wastes (HUW) and two mixtures (PT+HSL and PT+HUW) at a 50 % volume rate for their potential use as substrates with multiple applications. Ryegrass was established at a rate of 40 g seeds cm-2 in the potting mixtures. Hydrophysical and biochemical properties (microbial biomass and the enzymes dehydrogenase, β-glucosidase and phosphomonoesterase) were analyzed for PT, HSL, HUV and their combination (PT+HSL and PT+HUW). Treatments with biosolids hydrochar increased ryegrass production by 184% (HSL) and by 216% (PT+HSL) dry weight compared to the control (peat). Biochemical properties depended strongly on hydrochar type, while the hydrophysical properties of the hydrochars were similar to those of peat. Overall, our results found hydrochar-peat mixtures (PT+HSL and PT+HUW) to be suitable for the preparation of growing media.

Drylands cover more than 40% of terrestrial surface, and their global extent and socio-ecological importance will increase in the future due to the forecasted increases in aridity driven by climate change. Despite the essential role of metallic micronutrients in life chemistry and ecosystem functioning, it is virtually unknown how their bioavailability changes along aridity gradients at the global scale. Here we analysed soil total and available Cu, Fe, Mn, and Zn in 143 drylands from all continents, except Antarctica, covering a broad range of aridity and soil conditions. We found that total and available micronutrient concentrations in dryland soils were low compared to averages commonly found in soils of natural and agricultural ecosystems globally. Aridity negatively affected the availability of all micronutrients evaluated, mainly indirectly by increasing soil pH and decreasing soil organic matter. Remarkably, the available Fe:Zn ratio decreased exponentially as aridity increased, pointing to stoichiometric alterations. Our findings suggest that increased aridity conditions due to climate change will limit the availability of essential micronutrients for organisms, particularly that of Fe and Zn, which together with other adverse effects (e.g., reduced water availability) may pose serious threats to key ecological processes and services, such as food production, in drylands worldwide.

Heterotrophic soil microbial respiration-one of the main processes of carbon loss from the soil to the atmosphere-is sensitive to temperature in the short term. However, how this sensitivity is affected by long-term thermal regimes is uncertain. There is an expectation that soil microbial respiration rates adapt to the ambient thermal regime, but whether this adaptation magnifies or reduces respiration sensitivities to temperature fluctuations remains unresolved. This gap in understanding is particularly pronounced for drylands because most studies conducted so far have focused on mesic systems. Here, we conduct an incubation study using soil samples from 110 global drylands encompassing a wide gradient in mean annual temperature. We test how mean annual temperature affects soil respiration rates at three assay temperatures while controlling for substrate depletion and microbial biomass. Estimated soil respiration rates at the mean microbial biomass were lower in sites with higher mean annual temperatures across the three assayed temperatures. The patterns observed are consistent with expected evolutionary trade-offs in the structure and function of enzymes under different thermal regimes. Therefore, our results suggest that soil microbial respiration adapts to the ambient thermal regime in global drylands.

We lack a predictive understanding of the environmental drivers determining the structure and function of archaeal communities as well as the proteome associated with these important soil organisms. Here, we characterized the structure (by 16S rRNA gene sequencing) and function (by metaproteomics) of archaea from 32 soil samples across terrestrial ecosystems with contrasting climate and vegetation types. Our multi-“omics” approach unveiled that genes from Nitrosophaerales and Thermoplasmata dominated soils collected from four continents, and that archaea comprise 2.3 ± 0.3% of microbial proteins in these soils. Aridity positively correlated with the proportion of Nitrosophaerales genes and the number of archaeal proteins. The interaction of climate x vegetation shaped the functional profile of the archaeal community. Our study provides novel insights into the structure and function of soil archaea across climates, and highlights that these communities may be influenced by increasing global aridity.

Biochar production from manure wastes, including pig manure, could provide a valuable alternative to current waste management practices, while offering an opportunity to improve soil properties and to reduce the risk of contamination derived from the direct application of manure as a soil amendment. Two different biochar samples, produced from pig manure at 300 °C (BPC300) and 500 °C (BPC500) were used to evaluate the impact of biochar amendment on soil enzymatic activity and soil CO2 emissions. An incubation experiment was designed as follows: selected soil (S) was amended with pig manure (PC) and two pig manure biochars prepared at 300 °C (BPC300) and 500 °C (BPC500) at a rate of 8 wt%. All samples were incubated during 219 days. The results indicated that soil amendment with biochars decreased the carbon mineralization, in contrast to soil amended with the pig manure. Addition of pig manure increased dehydrogenase, phosphomonoesterase and phosphodiesterase activities, while B prepared at 300 °C resulted on a positive effect on dehydrogenase activity. In contrast, B prepared at 500 °C did not exhibit a positive effect on soil enzyme activity.

A full understanding of the agronomic and environmental potential of biochar, and especially its potential as a C sequestration strategy, requires a full comprehension of its effects on native soil organic matter (SOM), as well as of its interactions with other organic amendments co-applied to the soil. In a field experiment, we investigated changes in quantity and quality of SOM pools characterized by different protection mechanisms as affected by 20 t ha-1 of biochar added alone or combined with two different organic fertilizers (i.e., municipal solid waste compost and sewage sludge) 8 months after application. In particular, free, intra-macroaggregate, intra-microaggregate, and mineral-associated SOM fractions were separated and analyzed for organic C, total N, and stable isotopic ratios; further, diffuse reflectance infrared Fourier transform spectroscopy was used to examine functional group composition. Soil biomass C content, basal respiration, and metabolic quotient were also determined. Biochar and organic fertilizer application increased significantly SOM content. Biochar accumulated mainly in the free SOM pool, not protected by the soil mineral matrix. Especially noteworthy was the significant interaction effect found between the biochar and organic fertilizer factors on mineral-associated organic C content. This suggested a promoting action of biochar on C stabilization in organically-fertilized soils through the formation of organo-mineral complexes. Organically-fertilized soils had higher microbial C than unfertilized soils. Basal respiration and metabolic quotient, however, were not affected by any of the treatments. As a whole, our results support the potential of biochar application as a strategy to sequester C in soils.

Biochar can provide multiple benefits in the ecosystem. However, an important concern, which needs to be addressed, is the presence of phytotoxic compounds in some biochars. In this work seed germination and plant development are reported for three biochars prepared from wood, paper sludge plus wheat husks and sewage sludge on five higher plant species (cress, lentil, cucumber, tomato and lettuce). In general, seed germination was not affected except for the inhibition caused by wood biochar in several species and the inhibition induced by paper sludge biochar on lettuce. No inhibition of root growth was detected, but in some cases leaf and stem growth were inhibited. The results are significant in terms of advancing current understanding on the impacts of biochar on vegetative growth and linking those effects to biochar inherent properties.