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The Walker and Syers model predict that phosphorus (P) availability decreases with time leading to a final stage known as retrogression. We tested the validity of the Walker and Syers model in the Canary Islands, a soil chronosequence ranging from 300 years to 11 million years under recurrent episodes of atmospheric dust-containing P inputs. In particular, we compared our results with those from the volcanic soil chronosequences described in the Hawaii Islands and in Arizona, as they share key biological and/or geological characteristics. In three islands of the Canarian Archipelago, we selected 18 independent sites dominated by mature Pinus canariensis forests and grouped them into six age classes. For each site, soil samples were analyzed for known proxies of soil nitrogen (N), P and cations availability. We also analyzed the P. canariensis needles for N, P and cation contents. We found tendencies similar to those observed in other soil chronosequences: maximum N and P concentrations at intermediate ages and lower P concentrations in the older soils. The nutrient dynamics suggested that the older sites may indeed be approaching the retrogression stage but at lower rates than in other similar chronosequences. Differences from other chronosequences are likely due to the drier Canarian climate, the higher P deposition rates originating from the nearby Sahara Desert and the top soil horizon studied. Our results confirm the validity of the Walker and Syers model for the Canary Islands despite the influence that the high P deposition rates and the seasonally dry climate may have on soil development and P pools in P. canariensis ecosystems.

Atmospheric nitrogen (N) inputs in the Mediterranean Basin are projected to increase due to fossil fuel combustion, fertilizer use, and the exacerbation of agricultural production processes. Although increasing N deposition is recognized as a major threat to ecosystem functioning, little is known about how local environmental conditions modulate ecosystem function response to N addition, particularly in the context of Mediterranean-Basin ecosystems. Here, we assess how N addition affects important ecosystem properties associated with litter decomposition, soil physical-chemical properties, soil extracellular enzymatic activity and microbial abundance across three long-term N addition experimental sites in the Mediterranean Basin. Sites were located in El Regajal (Madrid, Spain), Capo Caccia (Alghero, Italy), and Arrábida (Lisbon, Portugal) and are all representative of Mediterranean shrublands. No common pattern for litter decomposition process or other studied variables emerged among the control plots of the studied sites. Nitrogen supply only affected soil pH, a major driver of decomposition, in two out of three experimental sites. Moreover, when we explored the role of N addition and soil pH in controlling litter decay, we found that the effects of these factors were site-dependent. Our results point out to local ecosystem features modulating N addition effects in controlling litter decomposition rates in Mediterranean ecosystems, suggesting that the responses of soil functioning to N deposition are site-dependent. These findings provide further knowledge to understand contrasting ecosystem responses to N additions based on a single field experiments.

According to EU regulations, member states shall take measures to encourage the recycling of biowaste in a way that fulfils a high level of environmental protection. In Spain, the separate collection of biowaste is only implemented in some regions. For this reason, a pilot scheme based on an information campaign and the location of a specific brown container for biowaste in specific zones of the city was carried out in Castelló de la Plana (Spain) over a period of six months. In this period, the collection and composition of the biowaste was monitored in depth with the goal of determining the evolution of the efficiency of the new collection system over time. In the zones, the quality rate in the biowaste container increased as the pilot study progressed, finally reaching 90%. The rate of biowaste separation also increased in the three zones over time, although in different ways, which means that there is greater collaboration on the part of citizens. On the other hand, an analysis of the rate of net biowaste daily collection from zones 2 and 3 has shown that their value increases as the rate of containerization of biowaste decreases. Therefore, to obtain better results it will be necessary to increase the containerization of biowaste, that is, to reduce the distance from the citizen to the container. It can thus be said that there is a positive evolution of the experience, which boosts confidence when it comes to implementing the system throughout the city.

Soil biogeochemical functioning in Mediterranean pine forests is characterized by the typical alternation between wet and mild (or cold) winters and dry and warm (or hot) summers in the Mediterranean climate, which restrict soil microbial activity to short periods and determine the unique properties of nutrient cycling in these ecosystems. Besides, soil dry-rewetting cycles are frequent in all seasons with a strong influence on soil microbial population and biogeochemical processes. Mediterranean regions are also affected by ongoing global climate change with decreasing precipitation, increasing temperature, increasing atmospheric water demand, and higher climatic variability that will exacerbate soil drying-wetting cycles. Finally, Mediterranean pine ecosystems are periodically exposed to intense and recurrent fires and other disturbances, such as insect pests and parasites, which affect the input and output of nutrients and their short- and long-term availability. I review here soil functioning in Mediterranean pine forests by looking at key indicators of carbon and nutrient cycling, such as microbial biomass, soil respiration, enzyme activity, and nutrient availability. Dry-rewetting cycles and forest disturbances affect in different degrees to C and nutrient cycling in pine forests, which may determine higher microbial activity and nutrient limitation than expected.

Background:According to EU regulations, member states shall take measures to encourage the recycling of biowaste in a way that fulfils a high level of environmental protection. In Spain, the separate collection of biowaste is only implemented in some regions. For this reason, a pilot scheme based on an information campaign and the location of a specific brown container for biowaste in specific zones of the city was carried out in Castellón de la Plana (Spain) over a period of six months. In this period, the collection and composition of the biowaste was monitored in depth with the goal of determining the evolution of the efficiency of the new collection system over time. Results:In the zones, the quality rate in the biowaste container increased as the pilot study progressed, finally reaching 90%. The rate of biowaste separation also increased in the three zones over time, although in different ways, which means that there is greater collaboration on the part of citizens. On the other hand, an analysis of the rate of net biowaste daily collection from zones 2 and 3 has shown that their value increases as the rate of containerization of biowaste decreases. Conclusions:In order to obtain better results in the biowaste quality rate it will be necessary to increase the containerization of biowaste, that is, to reduce the distance from the citizen to the container. It can thus be said that there is a positive evolution of the experience, which boosts confidence when it comes to implementing the system throughout the city.

Soil carbon losses to the atmosphere, via soil heterotrophic respiration, are expected to increase in response to global warming, resulting in a positive carbon-climate feedback. Despite the well-known suite of abiotic and biotic factors controlling soil respiration, much less is known about how the magnitude of soil respiration responses to temperature changes over soil development and across contrasting soil properties. Here we investigated the role of soil development stage and soil properties in driving the responses of soil heterotrophic respiration to temperature. We incubated soils from eight chronosequences ranging in soil age from hundreds to million years, and encompassing a wide range of vegetation types, climatic conditions and chronosequences origins, at three assay temperatures (5 °C, 15 °C and 25 °C). We found a consistent positive effect of assay temperature on soil respiration rates across the eight chronosequences evaluated. However, chronosequences parent materials (sedimentary/sand dunes or volcanic) and soil properties (pH, phosphorus content and microbial biomass) determined the magnitude of this temperature effect. Finally, we observed a positive effect of soil development stage on soil respiration across chronosequences that did not alter the magnitude of assay temperature effects. Our work reveals that key soil properties alter the magnitude of the positive effect of temperature on soil respiration found across ecosystem types and soil development stages. This information is essential to better understand the magnitude of the carbon-climate feedback and thus to establish accurate greenhouse gas emission targets. This research received funding from the European Union’s Horizon 2020 research and innovation program under Marie Sklodowska-Curie Grant Agreement 702057. M.D. was supported by an FPU fellowship from the Spanish Ministry of Education, Culture and Sports (FPU-15/00392). M.D. and F.T.M. are supported by the European Research Council (Consolidator Grant Agreement No 647038, BIODESERT). M.D-B. is supported by a Large Research Grant from the British Ecological Society (grant agreement n° LRA17\1193, MUSGONET). F.T.M and M.D-B. acknowledge support from the Spanish Ministry (project CGL2017-88124-R). PGP and M.D-B. are supported by a Ramón y Cajal grant from the Spanish Ministry of Science and Innovation (RYC2018-024766-I and RYC2018-025483-I, respectively). F.T.M. acknowledges support from the Generalitat Valenciana (CIDEGENT/2018/041).

Little is known about the role of biocrusts in regulating the responses of N2O and CH4 fluxes to climate change in drylands. Here, we aim to help filling this knowledge gap by using an 8-year field experiment in central Spain where temperature and rainfall are being manipulated (~ 1.9°C warming, 33% rainfall reduction and their combination) in areas with and without well-developed biocrust communities. Areas with initial high cover of well-developed biocrusts showed lower N2O emissions, enhanced CH4 uptake and higher abundances of functional genes linked to N2O and CH4 fluxes compared with areas with poorly developed biocrusts. Moreover, biocrusts modulated the responses of gases emissions and related functional genes to warming and rainfall reductions. Specifically, we found under rainfall exclusion and its combination with warming a sharp reduction in N2O fluxes (~ 96% and ~ 197%, respectively) only under well-developed biocrust cover. Warming and its combination with rainfall exclusion reduced CH4 consumption in areas with initial low cover of well-developed biocrust, whereas rainfall exclusion enhanced CH4 uptake only in areas with high initial cover of well-developed biocrusts. Similarly, the combination of warming and rainfall exclusion increased the abundance of the nosZ gene compared to the rainfall exclusion treatment and increased the abundance of the pmoA gene compared to the control, but only in areas with low biocrust cover. Taken together, our results indicate that well-developed biocrust communities could counteract the impact of warming and altered rainfall patterns on soil N2O and CH4 fluxes, highlighting their importance and the need to preserve them to minimize climate change impacts on drylands. A. L. is supported by a FPI fellowship from the Spanish Ministry of Economy and Competitiveness (BES-2014-067831). M.D-B. acknowledges support from the Marie Sklodowska-Curie Actions of the Horizon 2020 Framework Programme H2020-MSCA-IF-2016 under REA Grant Agreement No. 702057 (CLIMIFUN) and the BES Grant Agreement No. LRA17\1193 (MUSGONET). J.D acknowledges support from the Fundação para Ciência e Tecnologia (IF/00950/2014) and the FEDER, within the PT2020 Partnership Agreement and COMPETE 2020 (UID/BIA/04004/2013). This research was supported by the European Research Council (ERC Grant Agreements 242658 [BIOCOM] and 647038 [BIODESERT]), by the Spanish Ministry of Economy and Competitiveness (BIOMOD project, ref. CGL2013-44661-R and AGL2015-64582-C3-3-R project) and by the Comunidad de Madrid and European Structural and Investment Funds (AGRISOST-CM S2013/ABI-2717). F.T.M. acknowledges support from Generalitat Valenciana (BIOMORES project, ref. CIDEGENT/2018/041). B.K.S research on the topic of biodiversity and ecosystem functions is funded by Australian Research Council (DP170104634).

The role of soil biodiversity in regulating multiple ecosystem functions is poorly understood, limiting our ability to predict how soil biodiversity loss might affect human wellbeing and ecosystem sustainability. Here, combining a global observational study with an experimental microcosm study, we provide evidence that soil biodiversity (bacteria, fungi, protists and invertebrates) is significantly and positively associated with multiple ecosystem functions. These functions include nutrient cycling, decomposition, plant production, and reduced potential for pathogenicity and belowground biological warfare. Our findings also reveal the context dependency of such relationships and the importance of the connectedness, biodiversity and nature of the globally distributed dominant phylotypes within the soil network in maintaining multiple functions. Moreover, our results suggest that the positive association between plant diversity and multifunctionality across biomes is indirectly driven by soil biodiversity. Together, our results provide insights into the importance of soil biodiversity for maintaining soil functionality locally and across biomes, as well as providing strong support for the inclusion of soil biodiversity in conservation and management programmes. Combining field data from 83 sites on five continents, together with microcosm experiments, the authors show that nutrient cycling, decomposition, plant production and other ecosystem functions are positively associated with a higher diversity of a wide range of soil organisms. Marie Sklodowska-Curie We thank N. Fierer, M. Gebert, J. Henley, V. Ochoa, F. T. Maestre and B. Gozalo for their help with laboratory analyses; O. Sala, C. Siebe, C. Currier, M. A. Bowker, V. Parry, H. Lambers, P. Vitousek, V. M. Pena-Ramirez, L. Riedel, J. Larson, K. Waechter, W. Williams, S. Williams, B. Sulman, D. Buckner and B. Anacker for their help with soil sampling in Colorado, Hawaii, Iceland, New Mexico, Arizona, Mexico and Australia; the City of Boulder Open Space and Mountain Parks for allowing us to conduct these samplings; C. Cano-Diaz for her advice about R analyses; S. K. Travers for her help with mapping. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no. 702057. M.D.-B. is supported by the Spanish Government under a Ramon y Cajal contract RYC2018-025483-I. This research is supported by the Australian Research Council projects (DP170104634; DP190103714). S.A. and F.D.A. are funded by FONDECYT 1170995, IAI-CRN 3005, PFB-23 (from CONICYT) and P05-002 (from Millennium Scientific Initiative). N.A.C. acknowledges support from Churchill College, University of Cambridge; and M.A.W. from the Wilderness State Park, Michigan for access to sample soil and conduct ecosystem survey. B.K.S. acknowledges a research award from the Humboldt Foundation. J.-Z.H. acknowledges support from the Australia Research Council (project DP170103628); and A.G. from the Spanish Ministry (project CGL2017-88124-R). F.B. thanks the Spanish Ministry and FEDER funds for the CICYT project AGL2017-85755-R, the CSIC project 201740I008 and funds from 'Fundacion Seneca' from Murcia Province (19896/GERM/15). P.T. thanks K. Little for her help with laboratory analyses. S.C.R. was supported by the US Geological Survey Ecosystems Mission Area. Any use of trade, firm or product names is for descriptive purposes only and does not imply endorsement by the US Government. S.N. was funded by the Austrian Science Fund (grant Y801-B16). Public domain – authored by a U.S. government employee

This paper describes the laboratory-scale simulation of the behaviour of rejects from a biological-mechanical treatment (BMT) plant in Castell&oacute, n (Spain). For this purpose, four lysimeters were built, with different densities. Simulations were carried out for 7 weeks and leachate recirculation was applied to two of them. The experimental results allowed us to determine: (i) dirt in fractions, which was relatively high (up to 15% in some fractions) due to biological processes, (ii) the field capacity for this waste with similar values to other works, which varied depending on the experiment, (iii) variation in the biomass percentage which lowered after experiments in all cases (59.5% lower on average), and the rejects&rsquo, calorific value was higher after experiments (28.2% on average), (iv) the evolution of leachate properties with or without recirculation, where percolation, in addition to the dragging of soluble materials, stabilised waste, which diminished its biological activity. Rejects&rsquo, increased calorific value will allow combustible material to be recovered in the future as a way to exploit the energy potential stored in landfills.

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.

Soil nitrogen (N) availability is a key driver of soil-atmosphere greenhouse gas (GHG) exchange, yet we are far from understanding how increases in N deposition due to human activities will influence the net soil-atmosphere fluxes of the three most important GHGs: nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2). We simulated four levels of N deposition (10, 20 and 50 kg N ha−1 yr−1, plus unfertilised control) to evaluate their effects on N2O, CH4 and CO2 soil fluxes in a semiarid shrubland in central Spain. After 8 years of experimental fertilisation, increasing N availability led to a consistent increase in N2O emissions, likely due to simultaneous increases in soil microbial nitrification and/or denitrification processes. However, only intermediate levels of N fertilisation reduced CH4 uptake, while increasing N fertilisation had no effects on CO2 fluxes, suggesting complex interactions between N deposition loads and GHG fluxes. Our study provides novel insight into the responses of GHGs to N deposition in drylands, forecasting increases in N2O emissions, and decreases in CH4 uptake rates, with likely consequences to the on-going climate change.

This study assesses which factors are involved in the soil respiration (Sr) response to wetting-drying cycles in two Mediterranean ecosystems. We analysed Sr, mineral nitrogen, ion-exchange resin mineral nitrogen, and phosphate levels at weekly intervals over one year in two Mediterranean ecosystems with contrasting characteristics: a pine forest with high levels of organic matter and nutrients and a shrubland with low carbon and nutrients availability. Higher Sr was detected in the pine forest (0.12–0.76 g CO 2 m −2 hour −1 ) than in the shrubland (0.04–0.67 g CO 2 m −2 hour −1 ). For both sites, Sr increased during wet periods and decreased during dry periods. Compared with Sr in the pine forest, the trend observed for resin mineral nitrogen was the opposite. No pattern was observed for resin mineral nitrogen at the shrubland site, or for mineral nitrogen or phosphate at either site. The initial water status of the wetting-drying cycles determined the Sr response, whereas the length of the drought period before the rewetting event had no effect. The impact of the initial soil water content on Sr played a crucial role when the wetting-drying events occur in a dry soil, having a secondary role in wet soils. Finally, soil water status drove Sr during the growing season in both ecosystems; however, soil temperature had no effect on CO 2 efflux. In a changing world with projections of intensifying wetting-drying events, our results highlight the influence of soil water status on respiration rates, especially when these events occur in a dry soil.

Mechanical and biological treatments are the widespread treatments of mixed waste and organic waste in order to enable recovering recyclable materials from MSW. However, a large portion of mixed waste ends up as rejects, which can provide a remarkable energy content. Rejects can therefore become a solid recovered fuel (SRF) for incineration or co-incineration plants that meet the classification and specification requirements laid down in standard CEN/TS 15359 (2012). In this work, different flows of reject have been studied and identified, and different rejects have been characterized. The most important differences exist between rejects from the stages of recovery of recyclable materials and rejects from the stages of compost/bio-stabilized matter refinement. Rejects are composed mainly of combustible material, with low S, C and Hg contents, although rejects from the material recovery stage have a higher chlorine content than the others, due to their higher plastics content. Nevertheless, rejects from the material recovery stage have the most favourable SRF class code. Therefore, to take advantage of the fuel contained in the SRF it is necessary to examine the different reject flows from MSW treatment plants separately in order to improve the quality of SRF obtained from rejects.

Identifying the global drivers of soil priming is essential to understanding C cycling in terrestrial ecosystems. We conducted a survey of soils across 86 globally-distributed locations, spanning a wide range of climates, biotic communities, and soil conditions, and evaluated the apparent soil priming effect using 13C-glucose labeling. Here we show that the magnitude of the positive apparent priming effect (increase in CO2 release through accelerated microbial biomass turnover) was negatively associated with SOC content and microbial respiration rates. Our statistical modeling suggests that apparent priming effects tend to be negative in more mesic sites associated with higher SOC contents. In contrast, a single-input of labile C causes positive apparent priming effects in more arid locations with low SOC contents. Our results provide solid evidence that SOC content plays a critical role in regulating apparent priming effects, with important implications for the improvement of C cycling models under global change scenarios., The global ecological predictors of soil priming remain unclear. Here the authors conducted a global survey of soils from 86 global locations using an isotopic approach and find that in more mesic sites with high SOC concentrations, soil priming effects are more likely to be negative.

Mediterranean forests will experience more frequent and intense drought periods and extreme rainfall events in the coming decades. Concomitantly, drought-induced forest die-off is likely to increase. Changes in rainfall patterns and forest die-off directly influence soil microbial communities and activity and, consequently, carbon (C) and nitrogen (N) turnover, but their interactive effects have not yet been explored. We investigated the short-, and the long-term interactive effects of forest die-off and drying-rewetting cycles on soil C and N mineralization rates of a Mediterranean woodland. Soil samples collected under and out of the influence of holm oak (Quercus ilex) trees with different defoliation degrees (six healthy, six affected and six dead) were incubated under two contrasting water regimes (i.e. drying-rewetting cycles vs. constant soil moisture). Potential soil C and N mineralization responded differently to water regimes, with an overall 55% increase in C mineralization and a 22% decrease in N mineralization in the drying-rewetting cycle treatment compared to the constant moisture treatment. Holm oak decline decreased the response of C mineralization while increased the response of N mineralization to the drying-rewetting cycles at both the short- and the long-term. Moreover, N turnover showed a higher sensitivity to these environmental changes than that of C during most of the year. Our study provides solid evidence that an intensification of the drying-rewetting regimes can result in a decoupling of soil C and N cycles in Mediterranean forests and that forest die-off might enhance this decoupling at both the short- and the long-term, with important implications for the ecosystem functioning., This study was supported by the International Laboratory of Global Change (LINCGlobal, CSIC4540), the Spanish Ministry of Economy and Competitiveness grant VERONICA (CGL2013-42271-P), the Community of Madrid grant REMEDINAL3-CM (S2013/MAE-2719) and the FCT/MEC through national funds and the co-funding by the FEDER (PT2020 Partnership Agreement and COMPETE 2020, UID/BIA/04004/2013). The authors are especially grateful to David López-Quiroga and Ana Prado Comesaña for their excellent help in the field and laboratory and to Aldo Barreiro for his assistance with data and statistical analysis. AR was supported by the Spanish National Research Council (CSIC) in the JAE-doc modality co-financed by the European Social Fund (ESF) and by a Postdoctoral Grant of the Portuguese Science and Technology Foundation (SFRH/BDP/108913/2015).

The spatial variability (i.e. heterogeneity) of environmental variables determines a wide range of ecosystem features and plays a key role in regulating key ecosystem services. Wildfires are among the most significant natural disturbances that forests face, but our knowledge about their effect on ecosystem spatial variability is still limited. We used a 19-year fire chronosequence of natural, unmanaged Pinus canariensis C. Sm. ex DC forests to investigate how wildfires affect overall ecosystem spatial variability, as well as that of key faunal, plant and soil ecosystem attributes. The spatial variability of most soil variables and of the overall ecosystem tended to decrease after the fire and remain lower than the unburned plots even after 19 years. The spatial variability of plant-related variables, except for litter decomposition, as well as that of soil arthropods abundance, decreased more gradually than that of soil variables, reaching the lowest values in the plots burned 19 years before the survey. Our study provides evidence that wildfires are capable of significantly decreasing local-scale forest spatial heterogeneity through changes in the spatial variability of their different components, with likely yet unknown consequences for ecosystem functioning.

While diesel use represents one of the most important costs of the waste-collection process, the impact of eco-driving practices in this context has been surprisingly little addressed so far. Here, we present the results obtained by implementing eco-driving through the installation of in-board driving-assistance devices in a Spanish waste-collection fleet. Driving parameters and diesel use were monitored for over a year on 67 vehicles. An average fuel consumption decrease of 7.45% was observed, ranging from 1.86% to 11.50% according to the type of vehicle and to its waste-collection mechanism. Waste-transfer trucks that were not performing stop-and-go cycles displayed the highest values of fuel savings. In addition, eco-driving benefits obtained through real-time feedback did not tend to get lost over time, as fuel consumption remained remarkably steady. An average difference of only −0.45% between the first and the last month of monitoring was observed. After 14 months, an economic and environmental assessment of eco-driving implementation in the fleet was carried out. Nearly 120,000 L of diesel were economized, leading to substantial financial savings and to a significant exhaust emission decrease that was theoretically quantified in terms of CO2, CO, HC, NOx and PM. Overall, our results tend to show a highly positive environmental and economic impact of fuel-efficient driving in the waste-collection context.

Soil bacteria and fungi play key roles in the functioning of terrestrial ecosystems, yet our understanding of their responses to climate change lags significantly behind that of other organisms. This gap in our understanding is particularly true for drylands, which occupy ∼41% of Earth´s surface, because no global, systematic assessments of the joint diversity of soil bacteria and fungi have been conducted in these environments to date. Here we present results from a study conducted across 80 dryland sites from all continents, except Antarctica, to assess how changes in aridity affect the composition, abundance, and diversity of soil bacteria and fungi. The diversity and abundance of soil bacteria and fungi was reduced as aridity increased. These results were largely driven by the negative impacts of aridity on soil organic carbon content, which positively affected the abundance and diversity of both bacteria and fungi. Aridity promoted shifts in the composition of soil bacteria, with increases in the relative abundance of Chloroflexi and α-Proteobacteria and decreases in Acidobacteria and Verrucomicrobia. Contrary to what has been reported by previous continental and global-scale studies, soil pH was not a major driver of bacterial diversity, and fungal communities were dominated by Ascomycota. Our results fill a critical gap in our understanding of soil microbial communities in terrestrial ecosystems. They suggest that changes in aridity, such as those predicted by climate-change models, may reduce microbial abundance and diversity, a response that will likely impact the provision of key ecosystem services by global drylands.

Garcia-Velazquez, L., Gallardo, A. 2017. The global nitrogen cycle. A perspective for the terrestrial ecologist. Ecosistemas 26(1): 4-6. Doi.: 10.7818/ECOS.2017.26-1.02 The nitrogen (N) availability in the biosphere, the alteration of the global cycle, and its impact on the ecosystem are given by three key functional characteristics of the N cycle. First, the atmospheric N abundance allows both the biological and industrial fixation through the Haber-Bosch process, doubling the atmospheric N total inputs. Thus, the atmospheric N reservoir is the main source of the N cycle alteration, being the easiness to return to its original compartment the principal difference with the carbon (C) and phosphorus (P) cycles. Second, low concentrations of N in rock and soil minerals determines that in the long-term N limitation is mainly regulated by the biological fixation rate, being also dependent on the soil development and the presence of organic sedimentary rocks. Finally, an essential property of the N cycle in the biosphere is the high mobility of N across ecosystem boundaries through N-fixation, nitrification, denitrification and ammonification processes. All these properties cause that the fixed N molecule have multiples effects along its movement across different ecosystems, leading to acidification, eutrophication, alteration of albedo among other processes, and contributing substantially to climate change.

Aims Climate and human impacts are changing the nitrogen (N) inputs and losses in terrestrial ecosystems. However, it is largely unknown how these two major drivers of global change will simultaneously influence the N cycle in drylands, the largest terrestrial biome on the planet. We conducted a global observational study to evaluate how aridity and human impacts, together with biotic and abiotic factors, affect key soil variables of the N cycle. Location Two hundred and twenty-four dryland sites from all continents except Antarctica widely differing in their environmental conditions and human influence. Methods Using a standardized field survey, we measured aridity, human impacts (i.e. proxies of land uses and air pollution), key biophysical variables (i.e. soil pH and texture and total plant cover) and six important variables related to N cycling in soils: total N, organic N, ammonium, nitrate, dissolved organic:inorganic N and N mineralization rates. We used structural equation modelling to assess the direct and indirect effects of aridity, human impacts and key biophysical variables on the N cycle. Results Human impacts increased the concentration of total N, while aridity reduced it. The effects of aridity and human impacts on the N cycle were spatially disconnected, which may favour scarcity of N in the most arid areas and promote its accumulation in the least arid areas. Main conclusions We found that increasing aridity and anthropogenic pressure are spatially disconnected in drylands. This implies that while places with low aridity and high human impact accumulate N, most arid sites with the lowest human impacts lose N. Our analyses also provide evidence that both increasing aridity and human impacts may enhance the relative dominance of inorganic N in dryland soils, having a negative impact on key functions and services provided by these ecosystems.

Background and aims Nitrogen (N) deposition and climate change are a threat to the structure and function of drylands, where biocrust-dominated communities are prevalent. We aimed at evaluating the influence of N deposition, climate and edaphic properties of semiarid areas of Spain on soil microbial communities and N cycling.

Climate change and atmospheric nitrogen (N) deposition are two of the most important global change drivers. However, the interactions of these drivers have not been well studied. We aimed to assess how the combined effect of soil N additions and more frequent soil drying-rewetting events affects carbon (C) and N cycling, soil:atmosphere greenhouse gas (GHG) exchange, and functional microbial diversity. We manipulated the frequency of soil drying-rewetting events in soils from ambient and N-treated plots in a temperate forest and calculated the Orwin & Wardle Resistance index to compare the response of the different treatments. Increases in drying-rewetting cycles led to reductions in soil NO3- levels, potential net nitrification rate, and soil : atmosphere GHG exchange, and increases in NH4+ and total soil inorganic N levels. N-treated soils were more resistant to changes in the frequency of drying-rewetting cycles, and this resistance was stronger for C- than for N-related variables. Both the long-term N addition and the drying-rewetting treatment altered the functionality of the soil microbial population and its functional diversity. Our results suggest that increasing the frequency of drying-rewetting cycles can affect the ability of soil to cycle C and N and soil : atmosphere GHG exchange and that the response to this increase is modulated by soil N enrichment.

Climate and litter quality have been identified as major drivers of litter decomposition, but our knowledge of how soil characteristics (e.g. microbial community and chemical properties) determine carbon (C) and nitrogen (N) availability derived from the decomposition of litter of different qualities is still scarce. We conducted a microcosm experiment to evaluate how soils with contrasting microbial communities and soil properties (denoted Soils A and B hereafter, where Soil B has higher bacterial and fungal abundance, fungal:bacterial ratio, and organic C than Soil A) determine the availability of soil C (carbohydrates, proteins, amino acids and phenols) and N (dissolved organic and inorganic N, microbial biomass N and available N) during the decomposition of litter of contrasting quality (C:N ratios ranging from 20 to 102). We also evaluated the relative importance of soil characteristics and litter quality as drivers of C and N inputs to the soil during this process. Overall, higher soil C and N availability after litter decomposition was found in Soil B than in Soil A. Soil characteristics had a higher positive effect on soil C and N contents than litter quality during litter decomposition. We also found that changes in N availability and organic matter quality registered after litter decomposition, linked to different soil characteristics, were able to promote dissimilarities in the potential mineralization rates. In conclusion, our study provides evidence that soil characteristics (e.g. microbial communities and chemical properties) can be more important than litter quality in determining soil C and equally important for N availability during the decomposition of leaf litter.

The characteristics and properties of waste in a landfill, and its evolution over time, are difficult to estimate because of the heterogeneity of materials, biomass degradation, density, cover material, and infiltration of water. In this work, a lysimeter was used to simulate how refuse from mechanical-biological treatment (MBT) plants evolved in a landfill over a 45-day period. Water was added as a way to imitate the effects produced during rainy seasons. Field capacity and changes in the physical and chemical properties (volatile solids, biomass, and heating value) were analyzed. The results of this research show that the percentage of biomass lowers, and the heating value increases, after bringing about infiltration and percolation of water in the waste mass. Therefore in order to stabilize waste in a landfill, employing irrigation or leachate recirculation could be advisable. As the heating value increases after percolation, it could also be a good idea to recover the fuel material after stabilization.

Summary 1. Climate change will raise temperatures and modify precipitation patterns in drylands worldwide, affecting their structure and functioning. Despite the recognized importance of soil communities dominated by mosses, lichens and cyanobacteria (biocrusts) as a driver of nutrient cycling in drylands, little is known on how biocrusts will modulate the resistance (i.e., the amount of change caused by a disturbance) of the N cycle in response to climate change. 2. Here, we evaluate how warming (ambient vs. ~2.5 °C increase), rainfall exclusion (ambient vs. ~30% reduction in total annual rainfall) and biocrust cover (incipient vs. well-developed biocrusts) affect multiple variables linked to soil N availability (inorganic and organic N and potential net N mineralization rate) and its resistance to climate change during 4 years in a field experiment. We also evaluate how climate change-induced modifications in biocrust and microbial communities indirectly affect such resistance. 3. Biocrusts promoted the resistance of soil N availability regardless of the climatic conditions considered. However, the dynamics of N availability diverged progressively from their original conditions with warming and/or rainfall exclusion, as both treatments enhanced N availability and promoted the dominance of inorganic over organic N. In addition, the increase in fungal:bacterial ratio and the decrease in biocrust cover observed under warming had a negative indirect effect on the resistance of N cycle variables. 4. Synthesis. Our results indicate that climate change will have negative direct and indirect (i.e. through changes in biocrust and microbial communities) impacts on the resistance of the N cycle in dryland soils. While biocrusts can play an important role slowing down the impacts of climate change on the N cycle due to their positive and continued effects on the resistance of multiple variables from the N cycle, such change will progressively alter N cycling in biocrust-dominated ecosystems, enhancing both N availability and inorganic N dominance.

The use of biochar as a soil amendment is gaining interest to mitigate climate change and improve soil fertility and crop productivity. However, studies to date show a great variability in the results depending on raw materials and pyrolysis conditions, soil characteristics, and plant species. In this study, we evaluated the effects of biochars produced from five agricultural and forestry wastes on the properties of an organic-C-poor, slightly acidic, and loamy sand soil and on sunflower (Helianthus annuus L.) growth. The addition of biochar, especially at high application rates, decreased soil bulk density and increased soil field capacity, which should impact positively on plant growth and water economy. Furthermore, biochar addition to soil increased dissolved organic C (wheat-straw and olive-tree-pruning biochars), available P (wheat-straw biochar), and seed germination, and decreased soil nitrate concentration in all cases. The effects of biochar addition on plant dry biomass were greatly dependent upon the biochar-application rate and biochar type, mainly associated to its nutrient content due to the low fertility of the soil used. As a result, the addition of ash-rich biochars (produced from wheat straw and olive-tree pruning) increased total plant dry biomass. On the other hand, the addition of biochar increased the leaf biomass allocation and decreased the stem biomass allocation. Therefore, biochar can improve soil properties and increase crop production with a consequent benefit to agriculture. However, the use of biochar as an amendment to agricultural soils should take into account its high heterogeneity, particularly in terms of nutrient availability.

Dryland ecosystems account for ca. 27% of global soil organic carbon (C) reserves, yet it is largely unknown how cli- mate change will impact C cycling and storage in these areas. In drylands, soil C concentrates at the surface, making it particularly sensitive to the activity of organisms inhabiting the soil uppermost levels, such as communities domi- nated by lichens, mosses, bacteria and fungi (biocrusts). We conducted a full factorial warming and rainfall exclusion experiment at two semiarid sites in Spain to show how an average increase of air temperature of 2-3 °C promoted a drastic reduction in biocrust cover (ca. 44% in 4 years). Warming significantly increased soil CO2 efflux, and reduced soil net CO2 uptake, in biocrust-dominated microsites. Losses of biocrust cover with warming through time were par- alleled by increases in recalcitrant C sources, such as aromatic compounds, and in the abundance of fungi relative to bacteria. The dramatic reduction in biocrust cover with warming will lessen the capacity of drylands to sequester atmospheric CO2. This decrease may act synergistically with other warming-induced effects, such as the increase in soil CO2 efflux and the changes in microbial communities to alter C cycling in drylands, and to reduce soil C stocks in the mid to long term.

Dew is an important source of water in drylands, particularly for biological soil crusts (BSCs), which are soil communities dominated by lichens, mosses and cyanobacteria that are prevalent in these environments and play important roles in nutrient cycling. While BSCs can retain and use water from dew, the effects of dew events on the cycling of nitrogen (N) and carbon (C) in BSC-dominated ecosystems are largely unknown. We conducted an experiment to evaluate the effects of BSCs and dew on N and C cycling; intact soil cores from either bare ground or BSC-dominated microsites were incubated over 14 days under control and artificial dew addition treatments. A positive increment in the amount of total available N and phenols was observed in response to dew events under BSCs. We also found an increase in the concentration of dissolved organic N, as well as in the pentoses:hexoses ratio, under BSCs, suggesting that dew promoted an increase in the decomposition of organic matter at this microsite. The increase in the amount of available N commonly observed under BSCs has been traditionally associated with the fixation of atmospheric N 2 by BSC-forming cyanobacteria and cyanolichens. Our results provide a complementary explanation for such an increase: the stimulation of microbial activity of the microorganisms associated with BSCs by dew inputs. These effects of dew may have important implications for nutrient cycling in drylands, where dew events are common and BSCs cover large areas.

The influence of biological soil crusts (BSCs) on the small-scale spatial distribution of inorganic nitrogen (N) in drylands is largely unknown, despite their known impact and importance on the N cycle in these environments. We evaluated how perennial plants and BSCs affected small-scale spatial patterns of soil inorganic N (ammonium and nitrate) availability in a semiarid grassland from Spain. The data were analyzed by using geostatistical methods. The range of semivariograms for ammonium and nitrate, and the coefficient of variation of nitrate, were lower in BSC-dominated microsites than in plant-dominated microsites. Our results suggest that BSCs modulate the small-scale spatial pattern of inorganic N, producing more homogeneous conditions for spatial distribution of inorganic N forms than microsites provided by plants. These results may have important repercussions for the foraging strategies and ability of plant roots to uptake N.

This work analyses the separate collection systems used in Spanish towns with between 5000 and 50,000 inhabitants. The study looks at the systems and their efficiency by means of the indicators fractioning rate, quality in container rate and separation rate. The results obtained are compared with those from a similar study conducted earlier that was applied to towns and cities with populations over 50,000. It can be concluded that the most widely implemented system in Spain involves the collection of mixed waste from kerbside bins and picking up paper/cardboard, glass and lightweight packaging from drop-off points. Findings show that the best system is the one that collects mixed waste, organic material and multiproduct waste door-to-door, and glass from drop-off points. The indicator separation rate made it possible to establish beta regression models to analyse the influence of the following logistic variables: inhabitants per point (people/pt), time (years) and frequency of collection (freq). From these models it can be seen that people/pt has a negative effect on all the fractions, while freq and years have a positive effect in the case of paper.

Biological soil crusts (BSCs), composed of mosses, lichens, liverworts and cyanobacteria, are a key component of arid and semi-arid ecosystems worldwide, and play key roles modulating several aspects of the nitrogen (N) cycle, such as N fixation and mineralization. While the performance of its constituent organisms largely depends on moisture and rainfall conditions, the influence of these environmental factors on N transformations under BSC soils has not been evaluated before. The study was done using soils collected from areas devoid of vascular plants with and without lichen-dominated BSCs from a semi-arid Stipa tenacissima grassland. Soil samples were incubated under different temperature (T) and soil water content (SWC) conditions, and changes in microbial biomass-N, dissolved organic nitrogen (DON), amino acids, ammonium, nitrate and both inorganic N were monitored. To evaluate how BSCs modulate the resistance of the soil to changes in T and SWC, we estimated the Orwin and Wardle Resistance index. The different variables studied were more affected by changes in T than by variations in SWC at both BSC-dominated and bare ground soils. However, under BSCs, a change in the dominance of N processes from a net nitrification to a net ammonification was observed at the highest SWC, regardless of T. Our results suggest that the N cycle is more resistant to changes in T in BSC-dominated than in bare ground areas. They also indicate that BSCs could play a key role in minimizing the likely impacts of climate change on the dynamics of N in semi-arid environments, given the prevalence and cover of these organisms worldwide.

Dissolved organic nitrogen (DON) in soils has recently gained increasing interest because it may be both a direct N source for plants and the dominant available N form in nutrient-poor soils, however, its prevalence in Mediterranean ecosystems remains unclear. The aims of this study were to i) estimate soil DON in a wide set of Mediterranean ecosystems and compare this levels with those for other ecosystems; ii) describe temporal changes in DON and dissolved inorganic nitrogen (DIN) forms (NH + 4 and NO − 3 ), and characterize spatial heterogeneity within plant communities; and iii) study the relative proportion of soil DON and DIN forms as a test of Schimel and Bennett's hypothesis that the prevalence of different N forms follows a gradient of nutrient availability. The study was carried out in eleven plant communities chosen to represent a wide spectrum of Mediterranean vegetation types, ranging from early to late successional status. DON concentrations in the studied Mediterranean plant communities (0–18.2 mg N kg −1 ) were consistently lower than those found in the literature for other ecosystems. We found high temporal and spatial variability in soil DON for all plant communities. As predicted by the Schimel and Bennett model for nutrient-poor ecosystems, DON dominance over ammonium and nitrate was observed for most plant communities in winter and spring soil samples. However, mineral-N dominated over DON in summer and autumn. Thus, soil water content may have an important effect on DON versus mineral N dominance in Mediterranean ecosystems.

The purpose of this study was to identify the different selective collection systems implemented in Spanish cities and to analyse the efficiency and extent to which the targets proposed by current law are met in each case. After defining the indicators to be used to quantify the efficiency of a selective collection system, a survey was designed to gather the information needed to calculate them. This survey was sent out to all Spanish cities with a population of over 50,000 inhabitants. Four different selective collection systems were also identified. For each of the four cases the indicators were calculated and analyzed to determine which one was the best system. The best values were obtained from the system with separation in five fractions: paper/cardboard, glass and lightweight packaging at drop-off points, organic waste and mixed waste in kerbside bins. Two regression models (linear and exponential) were developed in systems with enough data to explain and predict the variation in the amounts of materials that were separated correctly into containers, depending on the distance between containers and citizens. Nevertheless, the percentages of separation at source of paper/cardboard and lightweight packaging are still far from reaching the targets set by law. © 2010 Elsevier Ltd. All rights reserved.

Biological soil crusts (BSCs) greatly influence the N cycle of semi-arid ecosystems, as some organisms forming them are able to fix atmospheric N. However, BSCs are not always taken into account when studying biotic controls on N cycling and transformations. Our main objective was to understand how BSCs modulate the availability of N in a semi-arid Mediterranean ecosystem dominated by the tussock grass Stipa tenacissima. We selected the six most frequent soil cover types in the study area: S. tenacissima tussocks (ST), Retama sphaerocarpa shrubs (RS), and open areas with very low (BS), low (LC) medium (MC) and high (HC) cover of well developed and lichen-dominated BSCs. The temporal dynamics of available N dynamics followed changes in soil moisture. Available NH 4 + -N did not differ between microsites, while available NO 3 - -N was substantially higher in the RS than in any other microsite. No significant differences in the amount of available NO 3 - -N were found between ST and BS microsites, but these microsites had more NO 3 - -N than those dominated by BSCs (LC, MC and HC). Our results suggest that BSCs may be inhibiting nitrification, and highlight the importance of this biotic community as a modulator of the availability of N in semi-arid ecosystems.

Nitrogen-fixing plants alter the chemical properties of the soil beneath plant canopies, particularly by concentrating nitrogen-rich organic matter. We hypothesize that the presence of a legume canopy inside a plot will more greatly influence the spatial structure of soil nitrogen (N) than phosphorus (P). We also investigated whether the effects of legume individuals on the soil properties beneath their canopies might be mediated by soil texture and water availability. Thus, we expected that the local effect of a legume canopy would be more conspicuous in nutrient-poor sandy soils than in nutrient-rich loamy soils. Moreover, the spatial pattern should differ during the wet (winter) and dry seasons (summer) because the microbial processes driving nutrient cycling are sensitive to water availability. To test these hypotheses, square plots (4 m × 4 m or 3 m × 3 m) were placed around isolated mature individuals of Adenocarpus viscosus in two pine forest stands of the Canary Islands (Spain) with contrasting soil textures (loamy and sandy soil). The spatial pattern and scale of microbial biomass-N (MB-N), dissolved organic-N (DON), and inorganic-N and -P fractions (NH 4 –N, NO 3 –N and PO 4 –P) were analyzed with geostatistical methods for two sampling dates (summer and winter). Soil variables with spatial structure demonstrated a greater spatial dependence in the loamy than sandy soil, with the exception of MB-N during summer. Except for NH 4 –N and NO 3 –N in winter plots, the spatial range was also lower in the sandy than the loamy soil. The legume canopy only had a clear effect on the spatial pattern of winter NH 4 –N, NO 3 –N, and DON in the sandy soil; no dependence was observed for PO 4 –P on the legume canopy in both soil types. Our results suggest that the presence of A. viscosus individuals may be an important source of spatial heterogeneity in the N content of the soil in these forests. However, soil texture and water content modulated the magnitude of the legume canopy effect on the spatial distribution of these N forms beneath canopies.

The concern that climate change may increase fire frequency and intensity has recently heightened the interest in the effects of wildfires on ecosystem functioning. Although short-term fire effects on forest soils are well known, less information can be found on the long-term effects of wildfires on soil fertility. Our objective was to study the 17-year effect of wildfires on forest net mineralization rates and extractable inorganic nitrogen (N) and phosphorus (P) concentrations. We hypothesize that (1) burned forest stands should exhibit lower net mineralization rates than unburned ones; (2) these differences would be greatest during the growing season; (3) differences between soil variables might also be observed among plots from different years since the last fire; and (4) due to fireresistant geochemical processes controlling P availability, this nutrient should recover faster than N. We used a wildfire chronosequence of natural and unmanaged Pinus canariensis forests in La Palma Island (Canary Islands). Soil samples were collected during winter and spring at 22 burned and unburned plots. We found significantly higher values for net N mineralization and extractable N pools in unburned plots. These differences were higher for the winter sampling date than for the spring sampling date. Unlike extractable N and N mineralization rates, extractable P levels of burned plots exhibited a gradual recovery over time after an initial decrease. These results demonstrate that P. canariensis forest soils showed low resilience after wildfires, especially for N, and that this disturbance might induce long-term changes in ecosystem functioning. Ministerio de Ciencia y Tecnología

Knowledge of the spatial pattern and scale of plant resources is important to aid in understanding the causes of this spatial pattern and their consequences on process at the population, community, and ecosystem levels. We tested whether the effect of individual plants on the soil properties beneath their canopies might be mediated by soil texture, since this soil property has great influence on the soil organic matter protection, the soil cation exchange capacity, and the nutrients diffusion rate. We hypothesize that variables directly related to organic matter (microbial biomass-N [MB-N] or dissolved organic-N [DON]), as well as soil nutrients interacting with soil secondary minerals (PO4-P and NH4-N), should more closely follow the plant canopy projection in sandy soils than loamy ones. We also expected a higher spatial range and dependence of NO3-N in sandy soils, although the spatial distribution should not necessarily be affected by the plant position. To test these hypotheses, we used square plots (8 m×8 m or 6 m×6 m) placed around isolated mature individuals of Pinus canariensis in both loamy and sandy soils in P. canariensis forests, with replicates in summer and winter. Spatial pattern and scale of MB-N, DON, and inorganic-N and -P were analyzed with geostatistical methods. In the summer sampling, all soil variables had lower spatial ranges in the loamy soil than the sandy soil. However, no clear trend was observed in the winter. The spatial dependence of NO3-N from the two sampling dates was higher for the sandy soil than the loamy soil. Kriged maps in the sandy soil revealed that the spatial distributions of the summer soil moisture, MB-N, DON, and PO4-P were all dependent on pine location. Our results suggested that the presence of P. canariensis individuals may be an important source of spatial heterogeneity in these forests. Soil texture may determine the magnitude of the pine canopy’s effect on the spatial distribution of chemical and biological soil properties when water content is scant, but it may have negligible effects under conditions of higher water availability.

The spatial heterogeneity of essential plant resources plays a crucial role in the structure, composition and productivity of many terrestrial ecosystems. Fires may affect both the availability and spatial pattern of soil nutrients. However, little is known about the effect of fire on the spatial pattern of soil resources. We hypothesized that shortly after a wildfire, the spatial patterns of soil mineral-N, organic labile-N (microbial biomass-N and dissolved organic-N) and extractable-P pools would become more clumped because of ash accumulation and post-fire deposition of litter around individual adult trees. To test this hypothesis, we used plots within a Pinus canariensis forest (with both Pinus canariensis and Adenocarpus viscosus present) and sampled them onemonth before and one month after a wildfire. Using geostatistical analyses, we examined the spatial patterns of soil mineral-N (NH4-N and NO3-N), dissolved organic-N (DON), microbial biomass-N (MB-N) and soil extractable-P (PO4-P). Burned plots of P. canariensis and A. viscosus both had values that were significantly greater than the unburned plots for all variables, except for DON in both cases, and the N:P ratio in the case of A. viscosus, which showed significantly lower values. Except for DON, we observed an increased spatial dependence and range after a fire for all studied variables in the P. canariensis plots (large individuals). However, in plots with A. viscosus (smaller individuals), we only found differences before and after the fire for the PO4-P and DON spatial patterns. Our results confirm the changes in the spatial structure of soil variables with fire, and suggest that, on a short-term basis, the physical structure of the plant community may determine the new spatial structure after fire, with a more clumped distribution around large surviving trees and shrubs. The spatial patch size of limiting resources has important consequences for the success of restoration of forest communities on burned areas.

Fire induces changes in ecosystem nutrient regimes and can cause major losses of N and P. Much has been written about the effect of fire on nutrient availability in soil;most studies have been concerned with the short-term effects of shock. The primary objective of our study was to discover the effect of forest fires on long-term N and P availability, for which we used the ion exchange membrane method in a chronosequence of forest fires (1987, 1990, 1994, 1998, 2000 and 2005). The study was conducted on the island of La Palma (Canary Islands, Spain) in October 2006. We hypothesized that a rapid increase in nutrient availability would occur after the fire, followed by a reduction due to erosion and leaching, and then gradual recovery and an eventual return to initial levels. NH4-N, NO3-N and mineral-N availability peaked significantly 1 year after the fire. However, 5 years after the fire the N levels were similar to those found on unburned land. P availability decreased significantly a year after the fire, but gradually recovered over time. The N and P availability ratio increased significantly after the fire, falling during the chronosequence, with the lowest levels found on the unburned land. These results confirm that fire produces (a) a rapid and short-term increase in N availability, without a long-term decline, and (b) a longterm reduction in P availability, which tends to recover over time after the fire.

The Landfill models and software applications are limited to the individual calculation of some of the variables. However, there are none that address all of them. This paper shows the development of a computational tool called LABWASTE.12 for designing all the variables related to landfills with construction and demolition waste (CD characterization and properties of natural/recycled debris; statistical correlation between population and area of the landfill; preliminary design of the vessel; slope stability and dams; evacuation perimeter ditch drains; leachate generation; design of storm water and leachate ponds, and pre-dimensioning; biogas generation; and, finally, sealing and closure in compliance with official regulations. This will make possible to obtain an estimate of the amount of aggregate, waterproofing, geotextile, fences, chimneys, dams, etc. required, as well as an analysis of the feasibility of use and overall budget and items

Mixed municipal waste is treated at waste recovery and composting plants. A portion of the material that enters the plant becomes refuse, which comprises different streams generated after the packaging selection stage and the compost refining phase. The percentage of combustible material contained in this refuse is considerable and recovering it is therefore a feasible proposition. The refuse from waste treatment plants can nowadays be considered a solid recovered fuel (SRF) with an acceptable value, according to the European standard EN 15359. This standard provides a classification for SRF in which the economic parameter is the net calorific value, the technical parameter is the chlorine content, and the environmental parameter is the mercury content. This paper presents the design of an SRF with a high market value according to European standards that comes from a recovery and composting plant. To this end, physical–chemical analyses of refuse were performed. Furthermore, a set of enhancements in the mechanical, electromechanical, and optical separation process have also been proposed.

Geostatistical descriptions of soil heterogeneity patterns for plant communities are abundant in literature, however no effort has been done to compare spatial structure of different nutrients, and to look for a common pattern in different plant communities. Furthermore, there is no information on the consequences of different soil spatial patterns on resource availability for plant populations. Conditional simulations on the spatial distribution of soil NH4-N and NO3-N were carried out in order to study the effect of contrasted patch sizes on N availability for individuals with increasing root system size. The semivariogram range (an indication of patch size) for soil NH4-N and NO3-N in six plant communities was found to be very variable, and was higher for soil NH4-N than for soil NO3-N in each community. A positive correlation was observed between organic matter and NH4-N spatial ranges in the six plant communities, but not between NO3-N and NH4-N. Probabilities of finding a high soil N concentration within simulated plant populations depended on N patch size and root system size. Thus, a population taking up NH4-N (higher spatial range values) would be more heterogeneous (i.e. individuals will have differing probabilities of finding a high soil N concentration) than the same population taking up NO3-N. Likewise, a seedling population taking up NH4-N or NO3-N would be more heterogeneous than a large tree population in the same area, where individuals would have similar probability of finding a high soil N concentration. These results showed that the spatial patch size of limiting resources has important consequences at the population level, since it determines the probability of finding a favorable site, and therefore differing performances of individuals within a population.

Geostatistical descriptions of soil heterogeneity patterns for plant communities are abundant in literature, however there is no information on the consequences of different soil spatial patterns on resource availability for plant populations. Conditional simulations on the spatial distribution of soil NH4–N and NO3–N were carried out in order to study the effect of contrasted patch sizes on nitrogen availability for individuals with increasing root system size. The semivariogram range (an indication of patch size) for soil NH4–N and NO3–N in six plant communities was found to be very variable, and was higher for soil NH4–N than for soil NO3–N in each community. A positive correlation was observed between organic matter and NH4–N spatial ranges in the six plant communities, but not between NO3–N and NH4–N. Probabilities of finding a high soil N concentration within simulated plant populations depended on N patch size and root system size. Thus, a population taking up NH4–N (higher spatial range values) would be more heterogeneous (i.e. Individuals will have differing probabilities of finding a high soil N concentration) than the same population taking up NO3–N. Likewise, a seedling population taking up NH4–N or NO3–N would be more heterogeneous than a large tree population in the same area, where individuals would have similar probability of finding a high soil N concentration. These results showed that the spatial patch size of limiting resources has important consequences at the population level, since it determines the probability of finding a favourable site and therefore differing performances of individuals within a population.

Floodplain forests are generally areas of high plant diversity compared with upland forests. Higher environmental heterogeneity, especially variation in belowground properties may help explain this high diversity. However, there is little information available on the spatial scale and pattern of belowground resources in floodplain forests. Geostatistics and coefficient of variation (CV) were used to describe the spatial variability of 20 soil properties ranging from essential plant nutrients, such as NH4 or PO4, to nonessential elements like Ti or V. The spatial variation of Si-to-(Al + Fe) ratio, an index of soil development, was also analyzed. Semivariograms and maps of selected properties were used to discriminate between the effect of flooding (and other mechanisms that may contribute to large scale trends in data) and local heterogeneity. The hypothesis that elements mainly cycled through biological processes (such as N) show different spatial properties than elements cycled through both biological and geological processes (such as P) or elements under strict geological control (such as Ti or V) is also presented. Redox potential was the most variable property (CV = 1.35) followed by mineral N, phosphate, organic matter, and carbon. Nonessential elements for organisms such as Si, Al, Ti, Rh, or V were less variable, supporting the hypothesis that biological control on soil properties leads to higher spatial variability. The range (the average distance within which the samples correlate spatially) varied between 3.89 m for water content to 18.5 m for the Si-to-(Al + Fe) ratio. The proportion of the total variance that can be modeled as spatial dependence (structural variance) was very variable, ranging between 0.34 for Fe and 0.96 for K. The addition of the large trend had a strong influence on the CV of most soil variables and created a gradient in C accumulation and the mineral weathering rate. The results suggest that flooding and other processes that are responsible for large spatial trends in the floodplain forest differentially affect biologically and geologically controlled variables with different turnover rates, thus providing a heterogeneous edaphic environment.

Summary In arid and semi-arid ecosystems, isolated trees have an important effect on soil properties, which can determine the structure and function of the herbaceous and soil fauna communities in these types of ecosystems. The effect of the presence of a tree canopy on the spatial properties of soil nutrients were studied in this work. The hypothesis stated that the effect of the tree on the soil will be different for nutrients with varied biogeochemical characteristics. Nutrients such as N, which is retained in the ecosystem by biological mechanisms, must have a spatial distribution that is different from P and K, involved in geochemical processes (they are part of soil minerals), and in turn have a different distribution from non essential elements for plants such as Na and Li. To test this hypothesis, soil samples were taken under and around a tree in a Mediterranean Dehesa ecosystem, characterized by the presence of isolated trees within a herbaceous matrix. The samples were taken every 2 m and then at 50 cm intervals in a regular grid of 20×20 m around a holm oak ( Quercus ilex ), in order to analyse the spatial properties, using geostatistical techniques. All nutrients showed different patterns of spatial distribution. Mineral-N (NH 4 +NO 3 ), like soil organic matter, presented higher concentrations which coincided with the tree canopy. The highest P concentrations occupied a space which was beyond the canopy projection. Potassium showed a lower spatial structure, with high concentrations which coincided with the position of the holm oak trunk, while Na and Li showed a sparse spatial structure and their distribution seems to be independent of the tree position. These results support the hypothesis that the presence of a tree differentially affects the spatial distribution of the various nutrients, depending on their biogeochemical characteristics.

In composting plants, aerobic fermentation could not to be complete and therefore, the fate of unstabilyzed wastes from the compost refining, uses to be landfill. This fact provokes an extra biogas generation in landfills, which contributes to greenhouse effect. In this work, the refuse of compost refining process has been subjected to an anaerobic fermentation. For that, in order to analyze their biogas generation, three samples of different composting plants have been selected. In one of these plants, the amount of biogas generation has been considerable, which involves a not complete stabilization of biowaste in the composting process.

The Dehesa are savannah-like ecosystems that occupy extensive areas in the mediterranean regions of Southern Spain and Portugal. The changes in the soil nitrogen (N) potential mineralisation rate, microbial biomass-N and available mineral N in soils were studied over 1 year in a Dehesa ecosystem, in the SW of Spain. The temporal variability of soil samples was compared by using the coefficient of variation of samples taken on a monthly basis. Spatial variability of the soil samples was measured by comparing the variograms generated with geostatistical techniques. The potential N mineralisation reached a maximum in the spring and summer samples, and a minimum in the autumn. However, the soil NH4+, NO3- and microbial biomass-N showed maximum levels in winter, compared with minimum levels in the spring and summer. The potential mineralisation rate showed a higher temporal variability in the samples taken under tree canopies, due to highest maximum and similar minimum levels reached during the sampling period. The potential mineralisation rate, microbial biomass-N and soil mineral N were higher under the tree canopies than in the open grassland. The spatial distribution of the soil organic matter and available NH4+ was strongly influenced by tree canopy size. The semivariograms were adjusted to a spherical model, indicating a maximum NH4+ variability at a certain distance from the tree crown diameter. The same was not the case for the spatial distribution of the soil NO3- from the tree crown. Our results indicate that the tree component of a Dehesa ecosystem is a major influence in the spatial and temporal heterogeneity of soils.

Climate change and global warming have worldwide adverse consequences. Biochar production and its use in agriculture can play a key role in climate change mitigation and help improve the quality and management of waste materials coming from agriculture and forestry. Biochar is a carbonaceous material obtained from thermal decomposition of residual biomass at relatively low temperature and under oxygen limited conditions (pyrolysis). Biochar is currently a subject of active research worldwide because it can constitute a viable option for sustainable agriculture due to its potential as a long-term sink for carbon in soil and benefits for crops. However, to date, the results of research studies on biochar effects on crop production show great variability, depending on the biochar type and experimental conditions. Therefore, it is important to identify the beneficial aspects of biochar addition to soil on crop yield in order to promote the adoption of this practice in agriculture. In this study, the effects of two types of biochar from agricultural wastes typical of Southern Spain: wheat straw and olive tree pruning, combined with different mineral fertilization levels on the growth and yield of wheat (Triticum durum L. cv. Vitron) were evaluated. Durum wheat was pot-grown for 2 months in a growth chamber on a soil collected from an agricultural field near Córdoba, Southern Spain. Soil properties and plant growth variables were studied in order to assess the agronomic efficiency of biochar. Our results show that biochar addition to a nutrientpoor, slightly acidic loamy sand soil had little effect on wheat yield in the absence of mineral fertilization. However, at the highest mineral fertilizer rate, addition of biochar led to about 20–30 % increase in grain yield compared with the use of the mineral fertilizer alone. Both biochars acted as a source of available P, which led to beneficial effects on crop production. In contrast, the addition of biochar resulted in decreases in available N and Mn. A maximum reduction in plant nutrient concentration of 25 and 80% compared to nonbiochar-treated soils for N and Mn, respectively, was detected. This fact was related to the own nature of biochar: low available nitrogen content, high adsorption capacity, and low mineralization rate for N; and alkaline pH and high carbonate content for Mn. Our results indicate that biochar-based soil management strategies can enhance wheat production with the environmental benefits of global warming mitigation. This can contribute positively to the viability and benefits of agricultural production systems. However, the nutrient–biochar interactions should receive special attention due to the great variability in the properties of biochar-type materials.

This paper presents, firstly, the influence of the geometry of a slope in the safety factor (SF). In order to do this, the SF is compared among three types of slopes: with berms every 7 m high and a dam at the toe, without berms and with a dam at the toe, and without berms nor dams. It was observed that, for the same inclination, the berms do not significantly influence the stability. However, the construction of an earth dam at the base increases safety, especially with little height and slope in waste with poor mechanical properties. On the other hand, a set of diagrams to learn, quickly and easily, the safety factor of a landfill slope has been developed. Thus, this set of diagrams allows calculations from the SF height (from 17 to 80 m) and slope inclination (from 45° to 14°) with values of effective cohesion of the waste (C'o) from 1 to 3 t/m2 and effective friction angle (F') of 10° to 25°.

Two types of measures have traditionally been used to monitor changes after disturbances in the nutrient availability of forest ecosystems: (1) soil nutrient pools and transformation rates and (2) foliar nutrient content. We used a wildfire chronosequence in natural and unmanaged Pinus canariensis forests to determine which kind of measure is more effective in discriminating between disturbed and undisturbed plots and to determine whether the different availability indices provide comparable and consistent results within the chronosequence and between different sampling dates. The results showed that (1) foliar N and P concentrations were the variables that best discriminated between the plots of the chronosequence, (2) the various soil N availability indices neither showed steady relationships nor predicted the plant nutrient availability, and (3) P availability indices showed steady relationships and predicted plant nutrient availability. Due to the changing nature of the soil N pools, repeated sampling over a long period of time could yield results different from those presented here. However, the large sampling effort required would favor the use of foliar nutrient concentrations as the most desirable first approach to the community’s nutritional status, especially when time or budget constraints are relevant.