Soil contamination by trace elements (TE) is a major environmental problem and much research is done into its effects on ecosystems and human health, as well as into remediation techniques. The ...Aznalcóllar mine accident (April 1998) was a large-scale ecological and socio-economic catastrophe in the South of Spain. We present here a literature review that synthesizes the main results found during the research conducted at the affected area over the past 20years since the mine accident, focused on the soil-plant system. We review, in depth, information about the characterization of the mine slurry and contaminated soils, and of the TE monitoring, performed until the present time. The reclamation techniques included the removal of sludge and soil surface layer and use of soil amendments; we review the effects of different types of amendments at different spatial scales and their effectiveness with time. Monitoring of TE in soil and their transfer to plants (crops, herbs, shrubs, and trees) were evaluated to assess potential toxicity effects in the food web. The utility of some plants (accumulators) with regard to the biomonitoring of TE in the environment was also evaluated. On the other hand, retention of TE by plant roots and their associated microorganisms was used as a low-cost technique for TE stabilization and soil remediation. We also evaluate the experience acquired in making the Guadiamar Green Corridor a large-scale soil reclamation and phytoremediation case study.
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•The Aznalcóllar mine accident was a large ecological and socio-economic catastrophe.•Monitoring and experimentation studies have been carried out in the area, over 20years.•Soil amendments increased pH and reduced availability of trace elements.•The soil-plant transfer of trace elements was evaluated to assess toxicity in the food web.•The Guadiamar Green Corridor is a large-scale soil phytoremediation case study.
• Here, we investigated the physiological and structural leaf responses of seedlings of two evergreen and two deciduous Quercus species, grown in a glasshouse and subjected to contrasted conditions ...of light (low, medium and high irradiance) and water (continuous watering vs 2-months drought). • The impact of drought on photosynthetic rate was strongest in high irradiance, while the impact of shade on photosynthetic rate was strongest with high water supply, contradicting the hypothesis of allocation trade-off. • Multivariate causal models were evaluated using d-sep method. The model that best fitted the dataset proposed that the variation in specific leaf area affects photosynthetic rate and leaf nitrogen concentration, and this trait determines stomatal conductance, which also affects photosynthetic rate. • Shade conditions seemed to ameliorate, or at least not aggravate, the drought impact on oak seedlings, therefore, the drought response on leaf performance depended on the light environment.
Aims
Root functions are multiple and essential for the growth and survival of terrestrial plants. The aim of this work was to analyse the main trends in the variation of root traits, their ...coordination with leaf traits and their relationships with soil conditions.
Methods
We measured the variation of 27 fine root traits (five morphological, 20 chemical and two isotopic signatures) in trees of seven species of a mixed plantation in a metal-contaminated and remediated site of Southern Spain.
Results
We found evidences supporting the existence of a root economics spectrum (RES). However, other dimensions were identified as being independent of the main RES: mainly the variation in the carbon concentration, the accumulation of trace elements associated with tolerance of metal-rich soils, and the fractionation of δ
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N as a time-integrated trait of mycorrhizal-mediated nutrition. In general, roots and leaves were functionally coordinated, although most of the trace elements showed strong root-leaf discordance. The soil conditions interacted with the fine root traits in feedback processes. The ability of tree roots to accumulate trace elements and to reduce their translocation to leaves is a desirable trait for the phytoremediation of metal-contaminated soils.
Conclusions
Roots are multifunctional. Understanding the variations in the root traits of trees will help us to predict both the responses of forests to global changes, including soil contamination, and the provision of soil-based ecosystem services.
Understanding which factors and rules govern the process of assembly in communities constitutes one of the main challenges of plant community ecology. The presence of certain functional strategies ...along broad environmental gradients can help to understand the patterns observed in community assembly and the filtering mechanisms that take place. We used a trait‐based approach, quantifying variations in aboveground (leaf and stem) and belowground (root) functional traits along environmental gradients in Mediterranean forest communities (south Spain). We proposed a new practical method to quantify the relative importance of species turnover (distinguishing between species occurrence and abundance) versus intraspecific variation, which allowed us to better understand the assemblage rules of these plant communities along environmental gradients. Our results showed that the functional structure of the studied plant communities was highly determined by soil environment. Results from our modelling approach based on maximum likelihood estimators showed a predominant influence of soil water storage on most of the community functional traits. We found that changes in community functional structure along environmental gradients were mainly promoted by species turnover rather than by intraspecific variability. Specifically, our new method of variance decomposition demonstrated that between‐site trait variation was the result of changes in species occurrence rather than in the abundance of certain dominant species. In conclusion, this study showed that water availability promoted the predominance of specific trait values (both in above and belowground fractions) associated to a resource acquisition or conservation strategy. In addition, we provided evidence that changes on community functional structure along the environmental gradient were mainly promoted by a process of species replacement, which represent a crucial step towards a more general understanding of the relative importance of intraspecific versus interspecific trait variation in these woody Mediterranean communities.
Soil biodiversity loss due to pollution may affect ecosystem services negatively. This environmental problem may be solved by phytoremediation, which is an effective strategy to manage and remediate ...contaminated areas. During this remediation process, the establishment of plant communities may improve soil fungal community structure and, in particular, may favour mycorrhizal symbiotic associations. As a consequence, afforestation of degraded lands will have different outcomes on fungal diversity and functionality, which will depend on the selected tree and shrub species.
We analysed soil fungal diversity and functional guilds by high-throughput sequencing of environmental DNA in a trace element contaminated area, part of a large scale phytoremediation project running for 20 years. We selected five habitats for comparison purposes: three under the canopy of selected tree species (wild olive, white poplar and stone pine), adjacent treeless areas (grassland) and non-remediated areas (bare soil).
Soil fungal diversity and richness seemed to be enhanced by phytoremediation. White poplar soil had the highest diversity and richness compared to wild olive and stone pine. Fungal communities were especially different between stone pine, with soils rich in organic C and high C:N ratio, and grassland soils.
We identified 9,428 fungal OTUs from which 1,283 were assigned to a unique functional guild; the most abundant belonging to saprotrophic, plant pathogenic and ectomycorrhizal functional guilds. Ectomycorrhizal fungi were more abundant in soils under ectomycorrhizal host trees. Saprotrophs were abundant in grassland and wild olive soils, while plant pathogens were abundant in non-remediated soils.
The remediation of soils (clean-up and amendment addition) allowed the natural establishment of grassland habitats throughout the study area, increasing fungal diversity, richness, taxonomy and functionality, when compared to non-remediated soils. Tree afforestation allowed the establishment of a forest type community bringing a further recruitment of fungal taxa, mainly the ectomycorrhizal fungal guild. Afforestation with different tree species showed species-specific effects on soil N, organic C, Ca and C:N ratio which led to increased spatial heterogeneity in areas with potential to recruit a wider diversity of fungi.
•Soil fungal diversity increased with afforestation of contaminated lands.•White poplar and stone pine favoured ectomycorrhizal fungal communities underneath.•Tree species identity are key in phytoremediation to recover ecosystem services.•Plant species life history determined functional guilds of soil fungi.
1. Understanding the proximate factors that govern the widespread mast-seeding process is a question of considerable interest that remains poorly understood. The identity and effect of these factors ...may vary among coexisting species that differ in leaf habit, potentially resulting in temporally asynchronous patterns of seed production. 2. In this study, we aim to identify the proximate causes of mast-seeding using two oak species with contrasting leaf habit that coexist in southern Spain, the deciduous Quercus canariensis and the evergreen Q. suber. Simultaneously, we review the literature on environmental drivers of mast-seeding in Mediterranean oaks, distinguishing between evergreen and deciduous species. 3. Our results indicate that Mediterranean oaks are primarily sensitive to weather, mast-seeding being strongly correlated with water availability and air temperature, mainly in the spring and summer. 4. The two study oak species were affected by weather in quite different ways, most likely because of different abiotic requirements as well as contrasting functional strategies of resource use and biomass allocation. Specifically, annual seed production in Q. canariensis was more severely limited by drought than in Q. suber, but responded positively to warmer spring temperatures. 5. Q. canariensis showed a large interannual variability, whereas Q. suber exhibited much more constant seed production. These two species also exhibited a very low level of synchrony in their temporal patterns of seed crop size, most likely due to phenological differences in the processes of flowering and seed maturation. 6. Synthesis. Our results indicate that weather plays a crucial role as a proximate driver of mast-seeding in Mediterranean oaks. We hypothesize that the current abundance of co-occurring species that differ in leaf habit could be altered under future climate change scenarios. The decline of seed production with drier conditions will be potentially greater in deciduous species, particularly those inhabiting wetter sites. Alternatively, the expected warmer temperatures could negatively affect evergreen species as a consequence of their more conservative strategy of biomass allocation. Our findings suggest that understanding how species with different functional or phenological attributes adjust their reproductive abilities to weather may enable us to infer the effects of ongoing environmental changes on population recruitment and dynamics.
Key message
This study reinforces the existence of the leaf economics spectrum in Mediterranean woody species, and demonstrates the strong influence of phylogeny, leaf habit and environmental context ...as main drivers of variability in structural and nutrient traits of leaves.
Leaf structural and nutrient traits are key attributes of plant ecological strategies, as these traits are related to resource-use strategies and plant growth. However, leaf structure and nutrient composition can vary among different habitats, leaf habits or phylogenetic groups. In this study, we measured 13 leaf traits (one structural—leaf mass per area, LMA—and 12 nutrient traits) in 98 Mediterranean woody species growing over a wide range of environmental conditions, with the final aim of discerning the main causes of leaf trait variability. The variance decomposition results show that phylogeny, leaf habit and habitat type affected in several ways the structural and nutrient traits studied. Leaf nutrient concentrations are strongly positively correlated amongst themselves, and negatively correlated with LMA, in accordance with the “leaf economics spectrum”. We found that leaf habit and phylogeny were important causes of variation in LMA and in a broad number of leaf nutrients (i.e., C, N, Mg, S, K), while other micronutrients seemed to be more dependent on the environment (i.e., Cu and Mn). In summary, our study reinforces the existence of the leaf economics spectrum in a broad pool of Mediterranean woody species, and demonstrates the strong influence of phylogeny, leaf habit and environmental context as the main drivers of variability in some leaf structural and nutrient traits.
Fungi play a key role in the functioning of soil in terrestrial ecosystems, and in particular in the remediation of degraded soils. The contribution of fungi to carbon and nutrient cycles, along with ...their capability to mobilise soil trace elements, is well-known. However, the importance of life history strategy for these functions has not yet been thoroughly studied. This study explored the soil-fungi relationship of two wild edible fungi, the ectomycorrhizal Laccaria laccata and the saprotroph Volvopluteus gloiocephalus. Fruiting bodies and surrounding soils in a mine-spill contaminated area were analysed. Isotope analyses revealed Laccaria laccata fruiting bodies were
N-enriched when compared to Volvopluteus gloiocephalus, likely due to the transfer of
N-depleted compounds to their host plant. Moreover, Laccaria laccata fruiting bodies δ
C values were closer to host plant values than surrounding soil, while Volvopluteus gloiocephalus matched the δ
C composition to that of the soil. Fungal species presented high bioaccumulation and concentrations of Cd and Cu in their fruiting bodies. Human consumption of these fruiting bodies may represent a toxicological risk due to their elevated Cd concentrations.
Extensive research efforts are devoted to understand fine root trait variation and to confirm the existence of a belowground root economics spectrum (RES) from acquisitive to conservative root ...strategies that is analogous to the leaf economics spectrum (LES). The economics spectrum implies a trade-off between maximizing resource acquisition and productivity or maximizing resource conservation and longevity; however, this theoretical framework still remains controversial for roots. We compiled a database of 320 Mediterranean woody and herbaceous species to critically assess if the classic economics spectrum theory can be broadly extended to roots. Fine roots displayed a wide diversity of forms and properties in Mediterranean vegetation, resulting in a multidimensional trait space. The main trend of variation in this multidimensional root space is analogous to the main axis of LES, while the second trend of variation is partially determined by an anatomical trade-off between tissue density and diameter. Specific root area (SRA) is the main trait explaining species distribution along the RES, regardless of the selected traits. We advocate for the need to unify and standardize the criteria and approaches used within the economics framework between leaves and roots, for the sake of theoretical consistency.
•Integrating ecosystem services into land management decision-making is a challenge.•An adapted framework for soil-related ecosystem services is needed; we present one.•It helps identify changes ...caused by soil management and policies impacting on soil.•It will be used to single out the most beneficial land management measures.•Consistent terminology and clarity enable practical application with stakeholders.
Despite numerous research efforts over the last decades, integrating the concept of ecosystem services into land management decision-making continues to pose considerable challenges. Researchers have developed many different frameworks to operationalize the concept, but these are often specific to a certain issue and each has their own definitions and understandings of particular terms. Based on a comprehensive review of the current scientific debate, the EU FP7 project RECARE proposes an adapted framework for soil-related ecosystem services that is suited for practical application in the prevention and remediation of soil degradation across Europe. We have adapted existing frameworks by integrating components from soil science while attempting to introduce a consistent terminology that is understandable to a variety of stakeholders. RECARE aims to assess how soil threats and prevention and remediation measures affect ecosystem services. Changes in the natural capital's properties influence soil processes, which support the provision of ecosystem services. The benefits produced by these ecosystem services are explicitly or implicitly valued by individuals and society. This can influence decision- and policymaking at different scales, potentially leading to a societal response, such as improved land management. The proposed ecosystem services framework will be applied by the RECARE project in a transdisciplinary process. It will assist in singling out the most beneficial land management measures and in identifying trade-offs and win–win situations resulting from and impacted by European policies. The framework thus reflects the specific contributions soils make to ecosystem services and helps reveal changes in ecosystem services caused by soil management and policies impacting on soil. At the same time, the framework is simple and robust enough for practical application in assessing soil threats and their management with stakeholders at various levels.
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