Dominance of particulate organic carbon in top mineral soils in cold regions

18 páginas.- 4 figuras.- 63 referencias.- Supplementary information The online version contains supplementary material available at https://doi.org/10.1038/s41561-023-01354-5The largest stocks of soil organic carbon can be found in cold regions such as Arctic, subarctic and alpine biomes, which are warming faster than the global average. Discriminating between particulate and mineral-associated organic carbon can constrain the uncertainty of projected changes in global soil organic carbon stocks. Yet carbon fractions are not considered when assessing the contribution of cold regions to land carbon–climate feedbacks. Here we synthesize field paired observations of particulate and mineral-associated organic carbon in the mineral layer, along with experimental warming data, to investigate whether the particulate fraction dominates in cold regions and whether this relates to higher soil organic carbon losses with warming than in other (milder) biomes. We show that soil organic carbon in the first 30 cm of mineral soil is dominated or co-dominated by particulate carbon in both permafrost and non-permafrost soils, and in Arctic and alpine ecosystems but not in subarctic environments. Our findings indicate that soil organic carbon is most vulnerable to warming in cold regions compared with milder biomes, with this vulnerability mediated by higher warming-induced losses of particulate carbon. The massive soil carbon accumulation in cold regions appears distributed predominantly in the more vulnerable particulate fraction rather than in the more persistent mineral-associated fraction, supporting the likelihood of a strong, positive land carbon–climate feedback.We thank all authors who gathered and published the raw data in the original studies that enabled this literature synthesis. P.G.-P. acknowledges support from the Spanish Ministry of Science and Innovation via the I+D+i project PID2020-113021RA-I00 and the TED project TED2021-130908A-C42 (funded by European Union—NextGenerationEU). Work at Lawrence Livermore National Laboratory by N.W.S. was performed under the auspices of the US DOE OBER, under contract DE-AC52-07NA27344 award #SCW1632. M.P. acknowledges financial support by the Comunidad de Madrid and the Spanish National Council of Scientific Researches research grant Atracción de Talento (grant number 2019T1/AMB14503).Peer reviewe

Efectos del uso de biochar sobre el cultivo y las propiedades del suelo en ecosistemas agrícolas semiáridos

En los ecosistemas agrícolas semiáridos, los suelos se encuentran sometidos a procesos de degradación generalizados como consecuencia de prácticas agrícolas intensivas, que unidas a factores climáticos de marcada aridez, favorecen los procesos de mineralización de la materia orgánica edáfica. En este contexto, cada vez es más necesario el empleo de enmiendas orgánicas para mejorar la calidad del suelo y el rendimiento de los cultivos. En la actualidad, la aplicación de residuos orgánicos como enmienda de los suelos está muy extendida. Esta práctica agrícola se debe a la abundancia y disponibilidad de residuos y a la escasez actual de materias tradicionales como la turba o el estiércol para la producción de enmiendas orgánicas. De este modo, el empleo de residuos orgánicos en agricultura se postula como una alternativa a la problemática ambiental asociada a su gestión e incluso se está estudiando íntegramente su potencial para el secuestro de C. Con base en ello, el biochar (sólido carbonoso fabricado para su aplicación en el suelo) se postula como una estrategia con gran potencial tanto para la gestión de residuos como para el secuestro de C. Además, el biochar se erige como una herramienta con gran proyección para la protección de los suelos frente a la degradación y la mejora de la sostenibilidad de la agricultura. El objetivo principal de este proyecto es estudiar el efecto de la aplicación de biochar elaborado con distintos materiales solo o combinado con enmiendas orgánicas sobre el cultivo y las propiedades químicas y biológicas de suelos agrícolas semiáridos. En el capítulo III, el objetivo es estudiar los efectos de la aplicación de biochar de residuos urbanos con diferentes condiciones pirolíticas sobre las propiedades químicas y biológicas del suelo, y estimar el riesgo de contaminación al emplear este tipo de biochar como enmienda orgánica en el suelo. Los resultados apuntan a la temperatura de pirólisis como el principal factor que afecta a las propiedades químicas del suelo al enmendarse con biochar. Además, el aumento de la temperatura de pirólisis disminuye la biodisponibilidad de los metales pesados en los suelos. El objetivo del capítulo IV es estudiar el efecto de la aplicación de biochar sobre las distintas fracciones de la materia orgánica de suelos agrícolas, evaluar la estabilidad del C orgánico del suelo tras el uso combinado de biochar con fertilizantes orgánicos (compost municipal y lodos de depuradora), y determinar el efecto del empleo de biochar solo o combinado con enmiendas orgánicas sobre el cultivo. Los resultados señalan que la aplicación de biochar combinado con enmiendas orgánicas a largo plazo promueve la acumulación de C orgánico en las fracciones de la materia orgánica y disminuye la mineralización del C del suelo. Además, la aplicación de biochar solo o combinado con enmiendas orgánicas no mejoro ni el rendimiento de las cosechas de cebada, trigo y camelina ni la calidad del grano de cebada. En el capítulo V, el objetivo es determinar los cambios en las actividades enzimáticas relacionadas con los ciclos del C, N y P en suelos agrícolas enmendados con biochar afectados en un contexto de cambio climático y estudiar cómo afecta la aplicación de biochar a la sensibilidad de la mineralización del C a la temperatura. Los resultados indican que el tratamiento con biochar disminuye la actividad enzimática y la sensibilidad de la mineralización del C del suelo a la temperatura bajo un escenario de cambio climático a corto plazo, lo que implica una aclimatación de la microbiota a condiciones adversas. ABSTRACT Soils in semiarid agricultural ecosystems are being submitted to generalized degradation processes because of intensive agricultural practices, which combined with acute arid climate factors, favor the mineralization processes of soil organic matter in these ecosystems. So much so that it is becoming more and more necessary and frequent the use of organic amendments to improve soil quality and crop yield. Currently the application of organic waste as soil amendments is very common. This agricultural practice is due to the abundance and availability of waste and the ongoing lack of traditional materials such as peat or manure for the production of organic amendments. This has led to the postulation of using organic waste as an alternative to the environmental problems associated with waste management as well as the integral study of its C sequestration potential. Biochar (a carbonous solid fabricated for soil application) is postulated as a strategy with great potential for waste management along with soil C sequestration. Also, biochar is seen as a tool with a bright future for the protection of soils against degradation and the improvement of sustainability in agriculture. The principal objective of this project is to study the effect of the application of biochar elaborated with different materials, alone or combined with organic amendment on crops and chemical and biological properties in semiarid agricultural soils. In chapter III, the objective is to study the effects of the application of urban waste biochar with different pyrolytic conditions on soil chemical and biological properties, and to estimate the potential pollution risk while employing this type of biochar as an organic amendment in soils. The results highlight the temperature of pyrolysis as the principal factor which affects soil chemical properties when amended with biochar. Increasing pyrolysis temperature also reduces the bioavailability of heavy metals in soils. The objective of chapter IV is to study the effect of the application of biochar in the different fractions of organic matter in agricultural soils, to evaluate the stability of organic C in agricultural soils after the combined use of biochar with organic fertilizers (municipal compost and sewage sludge), and to determine the effect of biochar application alone or combined with organic amendments on crop production. The results point out that the long-term application of biochar combined with organic amendments promote the accumulation of organic C in the organic matter fractions and reduce the mineralization of native C in soils. Also, the application of biochar alone or combined with organic amendments did not improve the barley, wheat and camelina crop yield nor the barley grain quality. In chapter V, the objective is to determine the changes in the enzymatic activities related to the C, N and P cycles in agricultural soils amended with biochar affected by climate manipulation, to evaluate the effect of the use of biochar on soil C mineralization in a climate change context, and to study how biochar application affects the temperature sensitivity of soil C mineralization. The results indicate that the treatment with biochar reduces the enzymatic activity and the sensitivity of the C mineralization of the soil at low temperature in a short-term climate change scenario, which implies an acclimation of the microbiota in adverse conditions

Hydrothermal treatment as a complementary tool to control the invasive Pampas grass (Cortaderia selloana)

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.Peer reviewe

Response of soil organic matter fractions to biochar and organic fertilizers – Results from a nine-year field experiment

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

The effects of biochar on soil organic matter pools are not influenced by climate change

The sustainability of Mediterranean croplands is threatened by climate warming and rainfall reduction. The use of biochar as an amendment represents a tool to store organic carbon (C) in soil. The vulnerability of soil organic C (SOC) to the joint effects of climate change and biochar application needs to be better understood by investigating its main pools. Here, we evaluated the effects of partial rain exclusion (∼30%) and temperature increase (∼2 °C), combined with biochar amendment, on the distribution of soil organic matter (SOM) into particulate organic matter (POM) and the mineral-associated organic matter (MAOM). A set of indices suggested an increase in thermal stability in response to biochar addition in both POM and MAOM fractions. The MAOM fraction, compared to the POM, was particularly enriched in labile substances. Data from micro-Raman spectroscopy suggested that the POM fraction contained biochar particles with a more ordered structure, whereas the structural order decreased in the MAOM fraction, especially after climate manipulation. Crystalline Fe oxides (hematite) and a mix of ferrihydrite and hematite were detected in the POM and in the MAOM fraction, respectively, of the unamended plots under climate manipulation, but not under ambient conditions. Conversely, in the amended soil, climate manipulation did not induce changes in Fe speciation. Our work underlines the importance of discretely taking into account responses of both MAOM and POM to better understand the mechanistic drivers of SOC storage and dynamics

Distribution of soil organic carbon between particulate and mineral-associated fractions as affected by biochar and its co-application with other amendments

The application of biochar to soils, either alone or combined with other amendments, represents a management practice aimed at storing carbon (C) while enhancing soil fertility. However, the long-term effects of biochar application on soil organic C protection against microbial decomposition are uncertain. This study investigated, in a 9-year-long-term field experiment, the protection of organic C by minerals and iron (Fe) in soils amended with biochar alone or combined with either municipal solid waste compost or sewage sludge. Particulate (not protected by minerals) and mineral-associated organic matter fractions were separated, quantified, and finally the Fe-mediated protection mechanisms were examined by Fe K-edge extended X-ray absorption fine structure spectroscopy. With respect to the unamended control soil, soils amended with biochar, especially when combined with municipal solid waste compost and sewage sludge, had 3 times greater content of particulate organic C. Biochar combined with municipal solid waste compost and sewage sludge also increased mineral-associated organic C content (1.5×), although the magnitude of the effect was smaller than for the particulate organic C fraction. The contents of Fe(III)-organic matter complexes in particulate and mineral-associated organic matter fractions of the amended soils were similar to those of the unamended soils. Hematite represented the main Fe oxide phase in the particulate organic matter fraction of all the soils as well as in the mineral-associated organic matter fraction of the unamended soils, whereas ferrihydrite was more abundant in the mineral-associated organic matter fraction of the amended soils. As a whole, the obtained results in general, and the positive effect on the mineral-associated organic matter possibly mediated by ferrihydrite occurrence in particular, highlight the potential of biochar, alone or in combination with other amendments, as a strategy to store and preserve C in soils

Hydrothermal carbonization as a sustainable strategy for integral valorisation of apple waste

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).Peer reviewe

Short-term response of soil respiration and soil enzymatic activities to biochar application in semiarid agricultural soils under a climate change scenario

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, \u3b2-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

Response of soil chemical properties, enzyme activities and microbial communities to biochar application and climate change in a Mediterranean agroecosystem

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

Soil respiration and soil organic matter pools in soils amended for 7 years with biochar combined with mineral and organic fertilizers

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, intraaggregate, 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