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The 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.

Mineral-associated organic carbon (MAOC) constitutes a major fraction of global soil carbon and is assumed less sensitive to climate than particulate organic carbon (POC) due to protection by minerals. Despite its importance for long-term carbon storage, the response of MAOC to changing climates in drylands, which cover more than 40% of the global land area, remains unexplored. Here we assess topsoil organic carbon fractions across global drylands using a standardized field survey in 326 plots from 25 countries and 6 continents. We find that soil biogeochemistry explained the majority of variation in both MAOC and POC. Both carbon fractions decreased with increases in mean annual temperature and reductions in precipitation, with MAOC responding similarly to POC. Therefore, our results suggest that ongoing climate warming and aridification may result in unforeseen carbon losses across global drylands, and that the protective role of minerals may not dampen these effects.

Preventing and reversing soil degradation is essential to maintaining the ecosystem services provided by soils and guaranteeing food security. In addition to the scientific community, it is critical to engage multiple stakeholders to assess the degree of soil degradation and mitigation strategies' impact and meet the United Nations' Sustainable Development Goals, European Union's Common Agricultural Policy, and other national and international goals. A semi‐structured questionnaire was distributed across countries participating in the EU Horizon‐2020 “Transforming Unsustainable management of soils in key agricultural systems in E.U. and China. Developing an integrated platform of alternatives to reverse soil degradation (TUdi).” Using farmers' associations and educational institutions as an intermediate to distribute the questionnaires was an effective strategy for gathering a high number of responses. Results from 456 responses to the questionnaire showed that farm country, size, type of agriculture, and educational level of farm managers were significantly associated with the farmers' perception of soil degradation issues. Farm size and type of agriculture were also correlated with applying a nutrient management plan. The implications of the results for soil conservation measures are discussed. Additionally, we highlight the potential of projects such as TUdi for creating collaboration networks to drive widespread adoption by farmers of technologies to reverse the degradation of agricultural soils.

Preventing and reversing soil degradation is essential to maintaining the ecosystem services provided by soils and guaranteeing food security. In addition to the scientific community, it is critical to engage multiple stakeholders to assess the degree of soil degradation and mitigation strategies' impact and meet the United Nations' Sustainable Development Goals, European Union's Common Agricultural Policy, and other national and international goals. A semi-structured questionnaire was distributed across countries participating in the EU Horizon-2020 “Transforming Unsustainable management of soils in key agricultural systems in E.U. and China. Developing an integrated platform of alternatives to reverse soil degradation (TUdi).” Using farmers' associations and educational institutions as an intermediate to distribute the questionnaires was an effective strategy for gathering a high number of responses. Results from 456 responses to the questionnaire showed that farm country, size, type of agriculture, and educational level of farm managers were significantly associated with the farmers' perception of soil degradation issues. Farm size and type of agriculture were also correlated with applying a nutrient management plan. The implications of the results for soil conservation measures are discussed. Additionally, we highlight the potential of projects such as TUdi for creating collaboration networks to drive widespread adoption by farmers of technologies to reverse the degradation of agricultural soils.

Discriminating between soil particulate organic carbon (POC) and mineral-associated (MAOC) can constrain the uncertainty of global SOC estimates. Despite that a massive amount of the global SOC stock is stored in cold regions such as arctic, subarctic and alpine biomes, and that these regions are warming faster than the global average, how C is distributed among fractions is not considered when assessing the contribution of cold regions to global land C-climate feedbacks. Here we combined field observations of POC and MAOC fractions in the mineral layer with experimental warming, to investigate whether SOC in cold regions is predominantly stored in the POC fraction, and whether this relates to higher SOC losses with warming than in milder biomes. We show that SOC in surface mineral soils (0 to 30 cm) is largely dominated by the POC fraction in both permafrost and non-permafrost soils, and in arctic and alpine ecosystems but not in subarctic environments. The experimental findings indicate that SOC is more vulnerable to warming in cold ecosystems compared to milder biomes, as mediated by higher warming-induced POC losses, which agrees with the previous pattern of POC dominance. Our comprehensive analysis suggests that the massive SOC accumulation in cold ecosystems is not only warming faster that the global average, but predominantly stored in the POC fraction, the fraction most vulnerable to anthropogenic climate warming.

Al compostaje a nivel nacional se le augura un buen futuro, ya que lleva un incremento sostenido en la producción en las últimas décadas y cada año se ponen en funcionamiento nuevas plantas de compostaje. Desde un punto de vista medioambiental se considera favorable por reciclar unos materiales que en el pasado su destino era el vertederom o la incineración y su aplicación agricola supone una mejora de la fertilidad sobretodo para la mayor parte de los suelos de nuestro país que son deficitarios en materia orgánica. Muchos muniicipios y mancomunidades está haciendo un gran esfuerzo en implantar la recogida selectiva lo que supondrá un incremento de la calidad del compost, ya que se incorporarán menos cantidad de inertes y metales pesados a la masa a compostar. Se han incorporado nuevas tecnologÍas al proceso y diseño de las plantas, como es el caso de estudio de plantas piloto, sistemas controlados de biooxidación y volteadoras. Es fundamental seguir trabajando en la calidad y comercialización del compost y para ello la administración pretende en breve sacar una nueva legislación sobre este tipo de producto.

© 2015, Springer Science+Business Media New York. Ecological transformations derived from habitat fragmentation have led to increased threats to above-ground biodiversity. However, the impacts of forest fragmentation on soils and their microbial communities are not well understood. We examined the effects of contrasting fragment sizes on the structure and functioning of soil microbial communities from holm oak forest patches in two bioclimatically different regions of Spain. We used a microcosm approach to simulate the annual summer drought cycle and first autumn rainfall (rewetting), evaluating the functional response of a plant-soil-microbial system. Forest fragment size had a significant effect on physicochemical characteristics and microbial functioning of soils, although the diversity and structure of microbial communities were not affected. The response of our plant-soil-microbial systems to drought was strongly modulated by the bioclimatic conditions and the fragment size from where the soils were obtained. Decreasing fragment size modulated the effects of drought by improving local environmental conditions with higher water and nutrient availability. However, this modulation was stronger for plant-soil-microbial systems built with soils from the northern region (colder and wetter) than for those built with soils from the southern region (warmer and drier) suggesting that the responsiveness of the soil-plant-microbial system to habitat fragmentation was strongly dependent on both the physicochemical characteristics of soils and the historical adaptation of soil microbial communities to specific bioclimatic conditions. This interaction challenges our understanding of future global change scenarios in Mediterranean ecosystems involving drier conditions and increased frequency of forest fragmentation.

The aim of this research was to assess the impact caused by a long-term pollution by fluoride and heavy metals in two soils (PS1 and PS2) near an aluminium smelter in Slovakia, on soil microbial biomass C (MBC), basal respiration, metabolic quotient (qCO2) water-soluble organic C (WSOC) and enzymes activities involved in the C, N and P biogeochemical cycles. An unpolluted soil was used as control (C0). Results obtained for soil fluoride content reflected a gradient of fluoride exposure in topsoils of contaminated sites. Decreases in microbial and enzymatic activities and in MBC to organic C ratio were found in PS2 site, which is closer to the smelter and exhibited the highest fluoride content. PS1-soil showed an extreme alkaline pH caused by leaching of waste effluents from the smelter dumping site, higher contents of Zn, Cu, Pb and Cd, significantly larger MBC, qCO2 and catalase and urease activities, and much larger basal respiration and dehydrogenase activity than PS2 and C0-soil. Phosphatase, b-glucosidase and BAA-protease were negatively correlated with WSOC, basal respiration and dehydrogenase activity, and showed some degree of inhibition in polluted sites. These results may indicate different responses of microbial communities to ecosystem disturbances, caused by the drastic changes in soil’s physicochemical properties as result of the long-term emissions of fly ash with high levels of contaminants that are still affecting soil microbial and enzymatic activities.