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The responses of plants and their associated microorganisms to trace elements (TE) in soils present different patterns depending on the plant species and the TE concentration. In this work, the behaviours of several plant species growing in the Guadiamar Green Corridor (GGC) (Seville, Spain), contaminated by the Aznalcóllar mine spill, are discussed. Soil fungal diversity and mycorrhizal symbioses with herbaceous and tree species in the area are also summarized. TE accumulation in wild herbaceous plants (Poaceae, Asteraceae, Brassicaceae, and Fabaceae) differed among families and species but, with some exceptions, most of them tended to exclude TE from their aerial biomass. Most of the studied afforested shrubs and tree species in the GGC revealed an exclusion strategy for most of the TE, meaning that these species could be adequate for TE phytostabilization. White poplar accumulated high concentrations of Cd and Zn in its aerial tissues, thus being a good candidate for phytoextraction and biomonitoring of these elements. In contrast, other two native Mediterranean trees, holm oak and wild olive, as well as eucalyptus trees, presented a behaviour of TE exclusion (except for Mn). The study of several native thistles revealed their suitability for bioenergy production, although Cd contents in these plants were usually high compared to reference levels. Regarding fungal mycorrhization, arbuscule abundance in herbaceous roots colonized by arbuscular mycorrhizal fungi (AMF) was reduced by soil contamination. In the case of ectomycorrhizal (ECM) fungi, soil contamination caused a reduction of hyphal development in holm oak. However, our results indicate that TE in soil do not affect root fungal Shannon diversity, richness or guild abundance underneath wild olive and stone pine plants. Finally, the edible fungal sporocarps studied in the GCC presented bioaccumulation of Cu, Zn, and, especially, Cd., The responses of plants and their associated microorganisms to trace elements (TE) in soils present different patterns depending on the plant species and the TE concentration. In this work, the behaviours of several plant species growing in the Guadiamar Green Corridor (GGC) (Seville, Spain), contaminated by the Aznalcóllar mine spill, are discussed. Soil fungal diversity and mycorrhizal symbioses with herbaceous and tree species in the area are also summarized. TE accumulation in wild herbaceous plants (Poaceae, Asteraceae, Brassicaceae, and Fabaceae) differed among families and species but, with some exceptions, most of them tended to exclude TE from their aerial biomass. Most of the studied afforested shrubs and tree species in the GGC revealed an exclusion strategy for most of the TE, meaning that these species could be adequate for TE phytostabilization. White poplar accumulated high concentrations of Cd and Zn in its aerial tissues, thus being a good candidate for phytoextraction and biomonitoring of these elements. In contrast, other two native Mediterranean trees, holm oak and wild olive, as well as eucalyptus trees, presented a behaviour of TE exclusion (except for Mn). The study of several native thistles revealed their suitability for bioenergy production, although Cd contents in these plants were usually high compared to reference levels. Regarding fungal mycorrhization, arbuscule abundance in herbaceous roots colonized by arbuscular mycorrhizal fungi (AMF) was reduced by soil contamination. In the case of ectomycorrhizal (ECM) fungi, soil contamination caused a reduction of hyphal development in holm oak. However, our results indicate that TE in soil do not affect root fungal Shannon diversity, richness or guild abundance underneath wild olive and stone pine plants. Finally, the edible fungal sporocarps studied in the GCC presented bioaccumulation of Cu, Zn, and, especially, Cd.

The responses of plants and their associated microorganisms to trace elements (TE) in soils present different patterns depending on the plant species and the TE concentration. In this work, the behaviours of several plant species growing in the Guadiamar Green Corridor (GGC) (Seville, Spain), contaminated by the Aznalcóllar mine spill, are discussed. Soil fungal diversity and mycorrhizal symbioses with herbaceous and tree species in the area are also summarized. TE accumulation in wild herbaceous plants (Poaceae, Asteraceae, Brassicaceae, and Fabaceae) differed among families and species but, with some exceptions, most of them tended to exclude TE from their aerial biomass. Most of the studied afforested shrubs and tree species in the GGC revealed an exclusion strategy for most of the TE, meaning that these species could be adequate for TE phytostabilization. White poplar accumulated high concentrations of Cd and Zn in its aerial tissues, thus being a good candidate for phytoextraction and biomonitoring of these elements. In contrast, other two native Mediterranean trees, holm oak and wild olive, as well as eucalyptus trees, presented a behaviour of TE exclusion (except for Mn). The study of several native thistles revealed their suitability for bioenergy production, although Cd contents in these plants were usually high compared to reference levels. Regarding fungal mycorrhization, arbuscule abundance in herbaceous roots colonized by arbuscular mycorrhizal fungi (AMF) was reduced by soil contamination. In the case of ectomycorrhizal (ECM) fungi, soil contamination caused a reduction of hyphal development in holm oak. However, our results indicate that TE in soil do not affect root fungal Shannon diversity, richness or guild abundance underneath wild olive and stone pine plants. Finally, the edible fungal sporocarps studied in the GCC presented bioaccumulation of Cu, Zn, and, especially, Cd.

Algae have an indisputable role in coastal ecosystems, but their accumulation and uncontrolled proliferation cause severe damage for the local municipalities. Fertilization with seaweed has been shown to increase soil fertility and crop production reducing ultimately the need for inorganic fertilizers. However, contradictory results of the compost effect have been reported. In the present work, we aimed at testing the suitability of three composted algae materials obtained in a previous study as soil amendments for vines. The composted materials consisted of pruning waste (P) and seaweed (S) mixed (henceforth, P2S1, P1S1 and P1S2, referring the number to the ratio of P to S). Overall, we observed an increase in soil organic matter, phosphorus (P) and potassium (K) in the soil treated in comparison with soils with inorganic fertilization. A moderate N soil enrichment (ca. 20%) was also detected. The leaf analysis reflected generally the greatest concentrations of NPK for the organic treatments, but this was remarkable only during the first year after seaweed application. A noticeable improvement in grape production was detected especially with the P1S1 compost without compromising grape quality although a decrease in sucrose content was noted with the compost with higher productivity (e.g. P2S1 and P1S1). This slight sucrose drop could be attributable to a greater water availability mediated by the compost or to a dilution factor of the sucrose content caused by a greater number of berries in those vines. These findings suggest that although monitoring of the long-term effects is needed, the use of seaweed amendments for agriculture could offer a cost-effective method for coastal municipalities to reduce excessive algae debris while also minimizing the impacts of inorganic fertilization.

Climate change, especially in Mediterranean countries, might have a detrimental effect on agro‑ecosystems and agricultural production, as well as on the price, quantity and quality of the products. This study assesses the potential impact of drought predictions on a faba bean crop, and evaluates the adoption of conservation tillage practices to reduce this effect. For this purpose, a rainfall exclusion experiment was carried out in a Mediterranean rotation in Southwest Spain, where a long-term tillage experiment was running since 2008. Soil water storage (SWS), crop productivity and mineral nutrition, plant ecophysiology and biomass quality, as well as the colonization of roots by arbuscular mycorrhizal fungi (AMF) and symbiotic Rhizobium bacteria were evaluated over one growth cycle to study the combined effect of different tillage systems - non-tillage (NT), reduced tillage (RT) and traditional tillage (TT)- and rainfall reduction. Rainfall reduction had a negative impact on faba bean germination on the TT system, and on its aboveground biomass across the three tillage systems, but did not affect grain production. The percentage of biomass yield reduction by rainfall exclusion was 30% for NT, 50% for RT and 20% for TT. In the case of RT, low yields were influenced by a high incidence of weeds under rainfall reduction. The negative effect of water exclusion was especially evident on photosynthesis rates and stomatal conductance across all tillage types, while leaf water potential was affected by drought only in the TT system. These ecophysiological indicators were positively associated to some variables of arbuscular mycorrhizal colonization and Rhizobium nodulation in roots. Changes in the patterns of symbiotic interactions in response to drought depended on the tillage type. We conclude that, despite no effect on soil water storage, in the conservation tillage systems the increase in the mycorrhizal colonization in roots, particularly under NT, could be beneficia

Uranium (U) contamination due to mining and metallurgical operations is a serious problem and poses a high potential threat to humans and other organisms. The application of amendments and/or plants, known as assisted phytoremediation, can accelerate the adsorption, complexation and precipitation processes in soil, and therefore can facilitate the restoration of U mining areas. This study located in the central-west of peninsular Spain was focussed on two different U mine waste dumps (MWD), where the assisted phytoremediation process was implemented. At each MWD, an area of 10 ha (approx.) was selected for sugar lime (SL) application, at a rate of 75 T ha −1. In addition, after SL addition, common grasses Cynodon dactylon, Secale cereale, and the leguminosae Vicia sativa were seeded. Evolution of soil physico-chemical properties and plant development was monitored for 69 months in Top, Medium and Low areas of both MWDs. The main results indicated a positive effect of the amendment, improving the development of the spontaneous and induced vegetation and the accumulation of soil organic matter. Values of pH were maintained in the range of the neutrality during all the experimentation period. In general, total concentrations of trace elements (including U) presented a high variability. Values were similar in the different studied areas of each MWD (Top, Medium and Low) and did not change in time. Trace elements contents were, in general, higher than those found in non-contaminated soils. However, U and Mn availability decreased with time, as well as the accumulation of trace elements (especially U and Mn) in the studied plants. Moreover, these contents were lower than the permitted limit for animal consumption. In conclusion, application of phytoremediation contributed to the stabilization of U within the soil-plant system, mainly by its positive effects on vegetation cover and the consequent increase in soil organic matter.

Purpose Seaweed blooms are an irregular but frequent phenomenon in many coastal areas and during the touristic season, can cause limitations for recreational use of beaches. Here, we propose composting of seaweed removed from the shoreline as alternative to current management practices (e.g. disposal in landfills or incineration). Methods A co-composting strategy with garden prune waste was chosen for the treatment of seaweed blooms removed from the beaches. Composting was performed in windrows of 10 m long, 1.5 m wide and 1 m high using different ratios of algae and garden prune residues (1:2; 1:1 and 2:1) at a composting facility in Rota (Cadiz, Spain). Results Characteristic temperature profiles consisting of a very brief mesophilic phase, a 15-20-day thermophilic phase (maximum of 50-70 degrees C) and a second mesophilic phase (40-35oC) after 30-50 days were observed. After curing for more than 160 days, a stabilized non-phytotoxic composted material (50-70 g kg(-1) C; 2-3 g kg(-1) N; C/N ratio of 21-27 and electrical conductivity between 1.8-2.4 mS cm(-1)) was obtained. Composting worked best using a 2:1 ratio (prune waste:algae). The composted organic material showed larger presence of stabilized lignin-derived compounds as assessed via nuclear magnetic resonance. No odors were detected during the composting process suggesting that open-air treatment is feasible. Conclusion The co-composting strategy provides a safe, local and sustainable approach to deal with seaweed blooms during peaks of recreational use and in situations where algae have to be removed.

Climate change, especially in Mediterranean countries, might have a detrimental effect on agro‑ecosystems and agricultural production, as well as on the price, quantity and quality of the products. This study assesses the potential impact of drought predictions on a faba bean crop, and evaluates the adoption of conservation tillage practices to reduce this effect. For this purpose, a rainfall exclusion experiment was carried out in a Mediterranean rotation in Southwest Spain, where a long-term tillage experiment was running since 2008. Soil water storage (SWS), crop productivity and mineral nutrition, plant ecophysiology and biomass quality, as well as the colonization of roots by arbuscular mycorrhizal fungi (AMF) and symbiotic Rhizobium bacteria were evaluated over one growth cycle to study the combined effect of different tillage systems - non-tillage (NT), reduced tillage (RT) and traditional tillage (TT)- and rainfall reduction. Rainfall reduction had a negative impact on faba bean germination on the TT system, and on its aboveground biomass across the three tillage systems, but did not affect grain production. The percentage of biomass yield reduction by rainfall exclusion was 30% for NT, 50% for RT and 20% for TT. In the case of RT, low yields were influenced by a high incidence of weeds under rainfall reduction. The negative effect of water exclusion was especially evident on photosynthesis rates and stomatal conductance across all tillage types, while leaf water potential was affected by drought only in the TT system. These ecophysiological indicators were positively associated to some variables of arbuscular mycorrhizal colonization and Rhizobium nodulation in roots. Changes in the patterns of symbiotic interactions in response to drought depended on the tillage type. We conclude that, despite no effect on soil water storage, in the conservation tillage systems the increase in the mycorrhizal colonization in roots, particularly under NT, could be beneficia

Diferentes modelos climáticos apuntan a un descenso significativo de las precipitaciones anuales en el sur de España para final del siglo, así como a un aumento en la recurrencia de episodios de sequía intensa, que afectarían especialmente a los sistemas agrícolas de secano. El manejo del suelo puede influir profundamente en la resistencia de estos sistemas a una disminución de los recursos hídricos. En este trabajo se ha evaluado si las técnicas de laboreo influyen en el funcionamiento de suelos de secano en un escenario probable de reducción de precipitaciones, incidiendo en aspectos relacionados con la actividad y diversidad de las comunidades bióticas del suelo. Para ello, se estableció un experimento de manipulación de lluvia (mediante casetas de exclusión) en un ensayo de laboreo de conservación de largo plazo, en el que se comparan tres alternativas de laboreo (convencional, reducido y no laboreo) en suelos de secano del Valle del Guadalquivir. Se realizó un seguimiento de la producción agrícola durante dos años (correspondientes a cultivo de haba y trigo dentro de la rotación), y se caracterizaron las principales propiedades físicoquímicas de los suelos, la actividad microbiana y la diversidad de hongos, bacterias y nematodos del suelo (0-10 cm). La sequía experimental produjo una disminución de la biomasa vegetal del cultivo de haba especialmente en el laboreo reducido (50 % de reducción), aunque no de su producción de grano. Durante el cultivo del trigo no se observó un impacto negativo de la sequía en la producción. En el no laboreo el contenido en nitrógeno del suelo fue significativamente mayor, independientemente del tratamiento hídrico. La exclusión de lluvia tuvo un efecto marginalmente significativo sobre el contenido en carbono orgánico de los suelos superficiales en el cultivo de haba; éste tendió a ser ligeramente superior en los suelos del tratamiento de exclusión de lluvia, posiblemente debido al aumento de la proporción raíz: vástago de las pl

Climate model forecasts indicate a significant drop in annual rainfall in southern Spain by the end of the century, which would especially affect rainfed agricultural systems (IPCC 2021). Soil management has a marked influence on the use of water resources (Madejón et al., 2023). In this work, it has been evaluated whether conservation tillage techniques (no tillage and reduced tillage) increase resistance to drought in non-irrigated soils in the expected scenario of reduced rainfall compared to traditional tillage. Aspects related to the activity and diversity of soil biotic communities are studied. A rain manipulation experiment was established in rainfed soils of the Guadalquivir Valley. Agricultural production was monitored for two years (broad bean and wheat in rotation), and the main physicochemical properties, microbial activity, fungal and bacterial diversity, and soil nematodes were characterized. The experimental drought produced a decrease in the plant biomass of the broad bean crop, especially in reduced tillage, although not in its grain production. The exclusion of rain had a marginally significant effect on the organic carbon content of the superficial soils in the broad bean crop, which was slightly higher in the soils of the exclusion treatment, possibly due to an increase in the root:shoot ratio of the plants. Drought did not produce significant effects on various indices of microbial activity (soil respiration and enzymatic activities). However, tillage significantly influenced the amount of microbial biomass and the colonization patterns of broad bean plants by arbuscular mycorrhizal fungi (being higher in non-tillage), which was positively related to the levels of plant water potential. The nematode community was affected by the type of tillage, such that the maturity and structure indices were higher under the no-tillage system, reflecting the negative effect of tillage on the populations of the genera of nematodes more sensitive to disturbance

Understanding the combined effects of soil amendments and inoculation of mycorrhizal fungi on the response of different plant species during the phytostabilization process of trace elements contaminated soils is a challenge. This task is more difficult but more realistic when studied under field conditions. We assess the combined effects of two amendment doses and mycorrhizal inoculation on the response of saplings of two tree species planted in a contaminated field. The amendments were a mix of sugar beet lime and biosolid compost. The inoculation treatments were made with a commercial inoculum of arbuscular mycorrhizal fungi for wild olive and ectomycorrhizal fungi for stone pine. Results showed a weak or null effect of the mycorrhizal inoculation on plant growth, survival and trace element accumulation. There was a significant increase on P nutrition for stone pine, growing on non-amended conditions. Soil amendments were very effective reducing trace elements availability and their accumulation in both plant species, especially in roots. However, the effects on plant biomass were species-dependent and contrasted; low-dose amendments increased the biomass of wild olive by 33.3%, but reduced by 28% that of pine. The high doses of amendments (60 T ha−1) produced some negative effects on plant growth and nutrition, probably related to the increase of soil salinity. Both plant species, stone pine and wild olive, have been proved to be adequate for phytostabilization of contaminated soils under Mediterranean climate, due to their drought tolerance and the low transfer of trace elements from root to shoot, thus reducing toxicity for the food web. To implement microbial-assisted phytoremediation approaches, a better understanding of the diversity and ecology of plant-associated microorganisms is needed. The use of indigenous fungi, locally adapted and tolerant to contamination, would be more suitable for phytostabilization purposes.

The restoration of mining areas, in particular if they are located near towns or villages, is essential to reduce their potential risks for human health and to minimize their visual impacts. In this study, we assess the rehabilitation of a waste rock pile adjacent to the town of Tharsis (SW Spain). We measured vegetation cover and its diversity, and chemical composition of plants and soil, twelve years after remediation by lime amendments, added topsoil and planted vegetation. In general, the applied measures were successful covering with woody vegetation the upper part of the waste rock pile, and providing a greening visual landscape for the town nearby. The most abundant species were the gum rockrose (Cistus ladanifer) and the legume shrub Retama sphaerocarpa, this latter species most probably introduced in the seedbank of the added topsoil. Also in the soil seedbank, probably arrived the invasive Acacia saligna, of fast growth. In contrast, the lower part of the slopes was almost devoid of vegetation. We interpret that partial failure in the rehabilitation process as due to the acid mine drainage, which caused downslope a decrease of soil pH and increased availability of trace elements, thus impeding growth and establishment of plants. In addition, some plants, like C. ladanifer, growing at the base of the rock pile, had concentrations of Cd above the maximum tolerable level for animals, therefore representing a toxicity risk. Finally, we propose here an alternative technique to restore waste rock piles, by sorting and selectively handling the extractive wastes, thus reducing infiltration rates, seepages and the negative effect of the acid mine drainage. Those modified waste rock piles will be rehabilitated by the addition of topsoil and planted vegetation, as successfully worked out in the upper slopes of the study site.

El crecimiento incontrolado y la acumulación de algas (especialmente las no nativas) afectan negativamente a la calidad del agua, al uso recreativo de las playas y al turismo. Toneladas de biomasa de algas se eliminan en vertederos o se incineran anualmente, aunque en ocasiones se hayan aplicado como enmiendas orgánicas a suelos en áreas costeras. Sin embargo, el uso de materiales no estabilizados en la agricultura puede causar problemas al suelo y a las plantas. Además, las algas se caracterizan por tener una relación C/N relativamente baja y una alta salinidad, problemas que podrían resolverse mediante el cocompostaje.En el proyecto financiado por la Fundación Tauw en Rota (Cádiz), proponemos la bioconversión de residuos de algas en un recurso rico en nutrientes a través del co-compostaje con restos de poda en distintas proporciones. El proceso tuvo una fase inicial en la que las temperaturas fueron superiores a 50ºC (fase termofílica) seguida de una fase mesófíla en la que la temperatura descendió hasta los 40-35ºC y una fase de maduración. La aireación se aseguró en volteos periódicos y la humedad se mantuvo en niveles cercanos a los óptimos (25-30%). No se detectaron problemas de olores medidos por olfatometría. Los productos obtenidos no presentaron problemas de fitotoxicidad ni alcanzaron valores superiores a 4 mS cm-1 de conductividad eléctrica. Sin embargo, la alta carga de arena que acompañaba a las algas bajó notablemente la concentración de MO y nutrientes una vez cribado el producto.

The use of woody nitrogen-fixing plant species as multipurpose and energy crops aims to enhance biomass yield while improving soil properties. Yet, the effectiveness of this option is still under debate especially the use of short rotation cropping in water and nutrient limited environments. This study investigated whether short rotation coppicing of four taxa of multipurpose biomass woody legume Leucaena spp. can improve soil conditions when grown for biomass under a Mediterranean environment. Biomass yield, mineral composition and heat value of the biomass and the mineral and organic matter content of soil were evaluated. Under favorable growing conditions, woody dry biomass production was up to 29 Mg ha(-1) year(-1) with slight but significant differences between the four taxa that were tested. After 11 years of cropping, the soil showed higher fertility and microbial activity compared to the uncropped plot. Leucaena cultivation increased soil nitrogen by 35 %, dehydrogenase activity by 98 %, and organic matter and carbon content (by 41 %). Annual cuttings resulted in the highest biomass production, followed by two and three year cuttings. The mineral composition and the calorific capacity of woody biomass make it suitable for commercial use as an energy source (generating on average 151 MW h ha(-1) year(-1)). In conclusion, short rotation coppicing of nitrogen-fixing woody species results in high biomass production rates with the restoration of degraded soils, constituting a sustainable agroforestry system for rural areas.

Los suelos proporcionan servicios ecosistémicos fundamentales para el bienestar humano. Sin embargo, con frecuencia están degradados y contaminados por las actividades mineras e industriales. El accidente de la mina de Aznalcóllar (Sevilla), en abril de 1998, fue una catástrofe ecológica y socioeconómica de gran repercusión internacional. La recuperación del área afectada por el vertido minero transformó una zona devastada y contaminada en el actual Paisaje Protegido Corredor Verde del Guadiamar. En este libro se recogen las ponencias presentadas en la Jornada de Investigación del XX Aniversario del Accidente Minero de Aznalcóllar, organizada en abril de 2018 por el Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS-CSIC). El tema central de este volumen es la recuperación de los suelos contaminados y la experiencia obtenida en los veinte años de investigación. Se tratan aspectos diversos, como los criterios para el diagnóstico y control de la contaminación, los métodos para recuperar suelos contaminados, la evaluación de los riesgos de toxicidad, la provisión de servicios ecosistémicos y la conectividad ecológica. También se recogen las crónicas de los primeros momentos y las actuaciones urgentes después del accidente. Por último, se resume el debate abierto sobre el reto que supuso la catástrofe ambiental y las oportunidades que se abrieron para la investigación y la conservación con la creación del nuevo espacio protegido.

The growing interest in bioenergy crops that do not compete with food production for land use has promoted the implementation of low‐input crops on marginal lands. However, these crops can be highly limited by the low soil nutrient and water availability in these lands. In this work, biosolid compost (BC) was applied to improve the quality of a degraded, C‐poor soil under Mediterranean conditions. We evaluated the effects of BC addition on soil physical, chemical and biochemical properties in a field experiment with two native species with potential as bioenergy crops (Cynara cardunculus and Silybum marianum). The addition of BC significantly increased soil C content from <0.9% to >1%, and produced a two‐fold increase in soil P availability. Respiration rates and microbial activity were only slightly improved by BC, while significant increases in the PLFA molar content assigned to general classes of bacteria were recorded. The beneficial effects of BC triggered the percentage of seed germination in S. marianum (from 64% in control plots to 85% in the compost treatment) as well as the production of biomass in both species (two‐fold increase in the second year). Application of BC led to increases in energy yield of 58% for C. cardunculus and of 71% for S. marianum. Considering the low economic cost of BC, its application on marginal soils in combination with C. cardunculus crops, producing much larger biomass than S. marianum, could be considered as an option for degraded Mediterranean soils.

Uranium (U) contamination due to mining and metallurgical operations is a serious problem and poses a high potential threat to humans and other organisms. The application of amendments and/or plants, known as assisted phytoremediation, can accelerate the adsorption, complexation and precipitation processes in soil, and therefore can facilitate the restoration of U mining areas. This study located in the central-west of peninsular Spain was focussed on two different U mine waste dumps (MWD), where the assisted phytoremediation process was implemented. At each MWD, an area of 10 ha (approx.) was selected for sugar lime (SL) application, at a rate of 75 T ha −1. In addition, after SL addition, common grasses Cynodon dactylon, Secale cereale, and the leguminosae Vicia sativa were seeded. Evolution of soil physico-chemical properties and plant development was monitored for 69 months in Top, Medium and Low areas of both MWDs. The main results indicated a positive effect of the amendment, improving the development of the spontaneous and induced vegetation and the accumulation of soil organic matter. Values of pH were maintained in the range of the neutrality during all the experimentation period. In general, total concentrations of trace elements (including U) presented a high variability. Values were similar in the different studied areas of each MWD (Top, Medium and Low) and did not change in time. Trace elements contents were, in general, higher than those found in non-contaminated soils. However, U and Mn availability decreased with time, as well as the accumulation of trace elements (especially U and Mn) in the studied plants. Moreover, these contents were lower than the permitted limit for animal consumption. In conclusion, application of phytoremediation contributed to the stabilization of U within the soil-plant system, mainly by its positive effects on vegetation cover and the consequent increase in soil organic matter.

In recent years increasing attention has been given to the potential use of contaminated lands for biofuel production, because these degraded soils cannot be used for food production. To establish these crops in Mediterranean contaminated areas, where the soil quality is usually very poor, the addition of soil amendments might be necessary to improve soil productivity. In addition, the use of crops with low water demands, adapted to these particular conditions of climate and soil contamination, is a key requirement. We studied the development of Cynara cardunculus and Silybum mariamun crops (both suitable for the production of biomass for biofuel uses under a Mediterranean climate) in trace element contaminated soils under field conditions. To our knowledge, this is the first such work under these particular experimental conditions (soil contamination and field trial). Soil physical (hydraulic), chemical, and biochemical properties were monitored for one year in experimental plots, where we tested the effects of the addition of two different amendments (sugar lime and biosolid compost) on soil functioning and crop productivity. Seed germination and plant biomass production were low, although amendment addition improved both parameters. The chemical and biological indicators (enzyme activities, PLFA profiles, and soil respiration) tended to be slightly improved by the amendments, especially sugar lime. The hydraulic properties of the soil in the experimental area were very deficient, and the effect of the amendments was not enough to improve them; this was probably the main cause of the general low productivity of these rain-fed crops, as water infiltrated poorly through the root zone. To improve crop productivity under these soil conditions, certain aspects could be improved: higher doses of amendments should be applied and deeper tillage of the soil after amendment addition should be performed to facilitate water infiltration

The restoration of mining areas, in particular if they are located near towns or villages, is essential to reduce their potential risks for human health and to minimize their visual impacts. In this study, we assess the rehabilitation of a waste rock pile adjacent to the town of Tharsis (SW Spain). We measured vegetation cover and its diversity, and chemical composition of plants and soil, twelve years after remediation by lime amendments, added topsoil and planted vegetation. In general, the applied measures were successful covering with woody vegetation the upper part of the waste rock pile, and providing a greening visual landscape for the town nearby. The most abundant species were the gum rockrose (Cistus ladanifer) and the legume shrub Retama sphaerocarpa, this latter species most probably introduced in the seedbank of the added topsoil. Also in the soil seedbank, probably arrived the invasive Acacia saligna, of fast growth. In contrast, the lower part of the slopes was almost devoid of vegetation. We interpret that partial failure in the rehabilitation process as due to the acid mine drainage, which caused downslope a decrease of soil pH and increased availability of trace elements, thus impeding growth and establishment of plants. In addition, some plants, like C. ladanifer, growing at the base of the rock pile, had concentrations of Cd above the maximum tolerable level for animals, therefore representing a toxicity risk. Finally, we propose here an alternative technique to restore waste rock piles, by sorting and selectively handling the extractive wastes, thus reducing infiltration rates, seepages and the negative effect of the acid mine drainage. Those modified waste rock piles will be rehabilitated by the addition of topsoil and planted vegetation, as successfully worked out in the upper slopes of the study site.