Skip to content

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 the study is carried out under field conditions.

A research team of the IRNAS-CSIC, in collaboration with researchers from EEZ-CSIC, has assessed the combined effects of two amendment doses (high and low doses) and mycorrhizal inoculation on the response of saplings of wild olive and stone pine, planted in a contaminated field site. The amendments were a mix of sugarbeet lime and biosolid compost. The inoculation treatments were made with a commercial inoculum of arbuscular mycorrhizal fungi for wild olive, while we used ectomycorrhizal fungi for stone pine. The experimental plot was located at the Guadiamar Green Corridor (Sevilla).

Results showed a weak or null effect of the mycorrhizal inoculation on plant growth, survival and trace element accumulation. There was only a significant increase on P nutrition for stone pine, growing on non-amended conditions. In general, the positive effect of mycorrhizal colonization on P nutrition is more evident under stress conditions and it can disappear under more favourable soil conditions.

The 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 (30 T ha-1) increased the biomass of wild olive by 33.3%, but reduced by 28% that of pine. On the other hand, 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 tolerance to drought and metals, and the low transfer of trace elements from root to shoot, thus reducing toxicity for the food web.

As a conclusion of this study, we highlight the importance of implementing microbial-assisted phytoremediation approaches, for which a better understanding of the diversity and ecology of plant-associated microorganisms is needed. The use of indigenous mycorrhizal fungi, locally adapted and tolerant to contamination, will favour to reach the phytostabilization purposes.

This study has been published in the Science of the Total Environment:

Madejón, P., Navarro-Fernández, C.M., Madejón, E., López-García, A., Marañón, T. (2021). Plant response to mycorrhizal inoculation and amendments on a contaminated soil, Science of the Total Environment, vol. 789, art. 147943.

The Aznalcóllar mine accident (Seville), in April 1998, was an ecological and socioeconomic catastrophe with important international impact. The remediation and restoration of the area affected by the mine spill transformed a devastated and contaminated area into the current Guadiamar Green Corridor Protected Landscape. Despite the successful recovery of the affected area, residual contamination is still present.

One of the main threats from the mine spill was the presence of potentially toxic trace elements, such as As, Cd, Pb and Tl, in the contaminated soil. Therefore, it exists a risk of toxicity due to their possible transfer from the soil to the food chain, since the contents of these elements at high concentrations can be harmful to livestock and wild animals, as well as to human health. A research team of the IRNAS-CSIC led by José Manuel Murillo, in collaboration with the researchers Paula Madejón, María Teresa Domínguez and Engracia Madejón, has published the book chapter entitled “Risks for the food chain in the Guadiamar Green Corridor”. In this chapter, most of the studies carried out in the Green Corridor, dealing with the transfer of trace elements at different levels within the food chain, during the 20 years since the accident are collected. In addition, the corresponding potential risks of toxicity for animals and for human consumption are evaluated.

Horse grazing in the Guadiamar Green Corridor (photo by M.T. Domínguez).

Three relevant case studies, conducted by IRNAS researchers, are described in more detail: the potential toxic effect on the horses that graze in the Green Corridor, the accumulation of trace elements in land snails, and the transfer and accumulation of these elements in mushrooms. Both snails and mushrooms are wild foods that can be collected in the Green Corridor and consumed by local residents.

Finally, it is clearly explained why the neighbours of the close villages of the Green Corridor must not collect any food product from the contaminated area, for human consumption.


Madejón P, Madejón E, Domínguez MT, Murillo JM (2020). Riesgos para la cadena trófica en el Corredor Verde del Guadiamar. In: P Madejón y T Marañón (eds.), Recuperación de suelos y provisión de servicios ecosistémicos en el Corredor Verde del Guadiamar, pp. 113-135. Editorial CSIC, Madrid.

The mine tailing accident occurring on April 1998 at Aznalcóllar (Seville, Spain) was a great ecological and socioeconomical disaster, with international impact. The remediation and restoration of that spill-affected area transformed a devastated and contaminated land into the current Protected Landscape of the Guadiamar Green Corridor.   

The Research Conference of the XX Anniversary of the Aznalcóllar Mine Accident was organized on April 2018 in the IRNAS-CSIC, Seville, as part of the transfer activities of the INTARSU project. Based on that Conference, the Editorial CSIC has published on July 2020 the book “Soil remediation and provision of ecosystem services in the Guadiamar Green Corridor” (in Spanish), edited by the INTARSU researchers Paula Madejón and Teodoro Marañón.

The final chapter of the book gathers the main topics raised during the roundtable which closed the meeting. In particular, the participants identified and discussed the main challenges and opportunities after the mine accident.    

The environmental disaster was a great challenge for the natural ecosystems within the Guadiamar Basin and for the economy of the affected area. Among the short-term challenges, it was priority the urgent cleaning and remediation of the polluted soils. At long-term, it was essential to maintain the monitoring and vigilance of the potentially toxic elements in the ecosystem. It was a relevant challenge to transmit to the local people that the toxicity risks were, although mitigated, still present and for long-term in the spill-affected area. From the conservationist perspective, the main challenge on middle- and long-term, was to consolidate the ecological corridor connecting Doñana and Sierra Morena; that ecological function should be compatible with the multiple use of the Protected Landscape. Looking at the future, a worrying challenge is the reopening of the mine; their activities must be compatible with the maintenance of environmental quality and healthy ecosystems. Finally, a pending challenge was remarked: to enforce the “polluter pays principle”.

Roundtable participants; from the left to the right, Teodoro Marañón (moderator), Miguel Ferrer, Emilio Galán, Paula Madejón, Francisco Cabrera, María Teresa Domínguez and Francisco Quirós.

At the same time, the recovery of the mine accident offered also new opportunities. The most relevant opportunity was the strong support to the environmental scientific research, in particular to fields like the remediation of soils contaminated by trace elements, and to the evaluation of potential toxicity of contaminants on plants and animals. The Guadiamar Green Corridor has been a large-scale natural laboratory where several remediation measures have been tested, and where the dynamics of trace elements have been monitored. For the conservationists, it was a real opportunity to have a privileged protected space (the Guadiamar river) able to connect the isolated populations of Doñana with the large populations of Sierra Morena. This newly protected area is also an opportunity to practice recreational activities and ecotourism. It was suggested as future opportunity for the Aznalcóllar mine, to develop new, cleaner technologies and more reliable exploitation systems.       


Marañón, T. (2020). Challenges and opportunities after the Aznalcóllar´s environmental disaster. In: P. Madejón and T. Marañón (eds.). Soil remediation and provision of ecosystem services in the Guadiamar Green Corridor, pp. 195-206. Editorial CSIC, Madrid (in Spanish).

ISBN: 978-84-00-10636-2

Interactions between plants and soil are responsible for providing numerous ecosystem services from forests, including carbon sequestration, protection from erosion, improved soil fertility and stabilization of contaminants.

In the XXV World Congress of the IUFRO (International Union of Forest Research Organizations), held at Curitiba, Brasil from September 29th to October 5th, a scientific session (number E8,d,g) was devoted to the topic “Plant-soil interactions in forests”.

1) Different tree species affect differently to soil properties. For example, soil pH underneath pines (Pinus pinea) and holm oaks (Quercus ilex) was lower than under other five tree species in the same study area. These soil pH differences have relevant consequences for the mobility of trace elements and their uptake by trees (Madejón et al., 2018, Catena 166: 34-43).

2) Soil mycobiota differed in diversity and composition under wild olive (Olea europaea), stone pine (Pinus pinea) and white poplar (Populus alba), and with adjacent treeless sites. The afforestation represented 100% increase of soil fungal diversity, compared with the remediated zones (only with pastures). A total of 6535 OTUs (operational taxonomic units) were estimated as the gamma diversity of soil fungi in the study area (Gil-Martínez et al., in preparation).

The functional diversity of soil fungi (according to the FUNGuild data base) was represented by three main functional groups: saprotrophs (68% of OTUs), pathogens/parasites (18%) and mycorrhizal fungi (12%). Within the mycorrhizal fungi group, arbuscular fungi were associated to soil samples under wild olive and treeless pastures, while ectomycorrhizal fungi were abundant in soil under poplar and pine.

3) The case of mycorrhizal fungi is relevant because of their symbiotic relations with trees. Ectomycorrhizal fungi communities were studied by sampling root tips of 40 holm oaks (Q. ilex) distributed along four sites of the Guadiamar Green Corridor. A total of 55 OTUs were identified, with average of 3.8 fungal species per tree. Soil properties influencing primarily the composition of mycorrhizal fungal communities were total soil carbon, and the concentration of Ca, Cu, Ni and Zn (López-García et al., 2018, Soil Biol Biochem 121: 202-211).

In turn, the composition of mycorrhizal fungal communities affected significantly the accumulation of P in leaves, and the transfer rate of Zn from soil to root (Gil-Martínez et al., 2018, Front Plant Sci : 1682).

4) Soil fungi have a relevant role degrading organic matter and cycling nutrients, by the action of extracellular enzymes. We have found that beta-glucosidase activity (enzyme contributing to cellulose degradation) was much higher in the soil under poplar and pines than in soil under wild olive or in pastures. A feedback process can be inferred, by which tree species influence composition and abundance of soil fungi, and the rate of enzyme activity, which in turn promote organic matter decomposition and release of nutrients, which are up-taken by trees (Gil-Martínez et al., 2018, Proceed. Mine Closure 2018, Leipzig, pp. 636-647).

In summary, there are complex interactions between the aboveground and belowground subsystems of the forest ecosystem. Several examples of tree-microbiota-soil feedback processes have been studied in the Guadiamar Green Corridor. Metal uptake by trees is influenced by soil pH, which in turn can be modified by litter decomposition and root exudates. The composition and diversity of soil fungi are affected by tree species identity; on the other hand, mycorrhizal fungal communities influence some tree processes, like leaf P concentration, and Zn transfer from soil to root. Trees influence on soil enzyme activities, which in turn affect nutrient cycling and their uptake by trees.

A pdf copy of the presentation slides can be consulted in Digital CSIC.

The XXXII Reunión Nacional de Suelos organized by researchers from the field of edaphology belonging to the University of Seville and the Institute of Natural Resources and Agrobiology of Seville (IRNAS-CSIC) took place in Seville (Spain) on 10-13 September 2019. This meeting is an initiative of the Spanish Society of Soil Science (SECS) that has been taking place since 1973 as they organize excursions to get to know different Spanish soils.

The meeting began with a session of posters and presentations framed within different themes (see Abstracts Book). Within the theme of “Study and recovery of contaminated soils” Marta Gil Martínez, predoctoral researcher at IRNAS-CSIC, presented a study on the fungal functional diversity in trace element contaminated soils from the Guadiamar Green Corridor.

In this study, the soil fungal communities were analyzed with a methodology of next generation sequencing in soils with different levels of contamination by trace elements and with different plant covers. The results showed that the phytoremediation plan established after the Aznalcóllar mining accident has favored the development of fungal communities by increasing their species richness and diversity. Both the type of vegetation covers and the properties of the soil determine the structure of the fungal communities. Under the poplar and pine trees, the communities of ectomycorrhizal fungi dominate, and under the wild olive and herbaceous species dominate arbuscular mycorrhizal fungi, due to the specific symbiosis of each type of vegetation with the fungi.

Access to the poster in this link:

Gil-Martínez M, López-García Á, Navarro-Fernández CM, Domínguez MT, Marañón T (2019). Fungal functional diversity in trace element contaminated soils from the Guadiamar Green Corridor. XXXII Reunión Nacional de Suelos (Seville).

In the following days we made three diverse and representative itineraries of the main soils and landscapes of Western Andalusia: 1) a protected and unique space in Europe, Doñana National Park; 2) a global example of restoration such as the Guadiamar Green Corridor, a protected area after the Aznalcóllar mining disaster, and finally 3) the Mediterranean soils of the valley and countryside of Carmona.

In the Doñana National Park, the researcher Luis Clemente (IRNAS-CSIC) explained the types of soils and the various ecosystems that Doñana include. In the Guadiamar Green Corridor we visited the Aznalcóllar mine and the researchers María Teresa Domínguez (University of Seville) and Engracia Madejón (IRNAS-CSIC) explained the details of the accident and the studies that have been carried out since then. In Carmona, we study two soil profiles with the help of Antonio Jordán (University of Seville).