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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).

 

Soil abiotic properties, such as texture, nutrient availability and water, are essential in the development of terrestrial plants. Mycorrhizal fungi, which are fungi living in symbiosis with plants roots, are also key for plant growing. This symbiosis enhances a trade-off of carbohydrates and nutrients beneficial for both plant and fungi. Therefore, it is expected that different mycorrhizal fungal communities (in terms of species and their morphological traits) would affect plant development (in terms of plant chemical and morphological traits) in different ways.

In order to understand this mycorrhizal fungi-plant relationship, researchers from IRNAS-CSIC and Universidad de Sevilla (Spain), in collaboration with researchers from the University of Copenhagen (Denmark) and the University of Reading (United Kingdom), developed a study on holm oak trees and their symbiotic ectomycorrhizal fungi. The area selected for this study, known as the Guadiamar Green Corridor (Seville), suffered a mine spill leaving behind hectares of land contaminated by trace elements. Twenty years after the accident and the phytoremediation of the affected area, trace elements are still present and the role of ectomycorrhizal fungi might be especially important in this stressful environment.

In this study, we found that ectomycorrhizal fungi explained more than soil abiotic properties for most of the measured plant traits, especially root functional traits. The symbiosis with abundant species of ectomycorrhizal fungi (Hebeloma cavipes and Thelephora terrestris) was related to conservative positions into the root economics spectrum. Conservative traits, like denser roots and higher dry matter content, allow tree survival under adverse conditions. Hebeloma cavipes and Thelephora terrestris were characterised with a high rhizomorph formation, a fungal trait that enhances water and phosphate uptake through a long-distance exploration mechanism. It may be possible that this specific tree-fungi symbiosis was established as a consequence of resource limitations.

Trace element mobility through the soil-root-leaf continuum was analysed and despite soil trace elements concentrations in our environmental gradient was relatively large, accumulation of trace elements in oak leaves was relatively low. This confirms that holm oak is a suitable species for the phytostabilisation of contaminated soils, given its ability to prevent trace element accumulation into aboveground biomass. However, it is not the role of the tree alone, as trace element transfer was highly explained by its associated ectomycorrhizal fungal communities, which suggests that interactions with fungi play an important role at determining the capacity of this tree species to retain trace elements into its roots.

These findings support that ectomycorrhizal fungal community composition and their functional traits mediate plant performance in trace element contaminated soils, and have a high influence on plant capacity for phytoremediation of contaminants.

The study has been published in the journal Frontiers in Plant Science:

Gil-Martínez, M., López-García, Á., Domínguez, M. T., Navarro-Fernández, C. M., Kjøller, R., Tibbett, M., & Marañón, T. (2018). Ectomycorrhizal Fungal Communities and Their Functional Traits Mediate Plant–Soil Interactions in Trace Element Contaminated Soils. Frontiers in Plant Science, 9, 1682.