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Fungi are a fundamental component of the soil microbiome, with essential ecosystem functions. They contribute to the nutrient cycling, through the organic matter decomposition; forming symbiotic associations with plants (mycorrhizas) they allow to explore a greater volume of soil to capture water and nutrients; on the other hand, pathogen fungi regulate plant populations.

A research team of the IRNAS-CSIC, in collaboration with researchers from the universities of Seville, Jaén and Copenhagen, has studied the soil fungal diversity and its relations with tree species in the Guadiamar Green Corridor (Seville, Spain). This area was remediated and afforested after a mine-spill contamination episode in 1998.   

Using high-throughput sequencing of environmental DNA allowed to identify more than 9,000 different fungal “species” (OTUs, operational taxonomic units) in 50 soil samples from two contrasted sites in the Green Corridor. In the South site (Quema), the highest fungal diversity was found under white poplar (Populus alba), with average of 1,168 species per tree, belonging to 141 different families. While under wild olives (Olea europaea var. sylvestris), the average diversity was 599 species of 95 families. In contrast, non-remediated soils, where the mine sludge was not cleaned up, and were not remediated neither afforested, had a low fungal diversity: average of only 51 species per sample and 20 families. Although these fungal species have interest due to their tolerance to extreme conditions of soil acidity and high concentration of potentially toxic elements.       

Venn diagram with fungal diversity in each habitat type.

We start to discover the magnitude of the soil biodiversity: hundreds or thousands of species in each sample, but we still ignore the functionality of all those species. The comparison with the existing database -FUNguild- allowed to assign the functional group for a 13.6% of the species recorded in the Green Corridor study. Within this representative sample (1,283 species), the dominant functional group was the saprothrophs fungi, which decompose organic matter and contribute to nutrient cycling, and were more tied to wild olive and grassland soils. The second most abundant group was the plant pathogens, mainly found in non-remediated soils. The third group, ectomycorrhizal fungi, was especially abundant in soils under trees, like pines and poplars, forming symbiotic associations with them.     

Tree planting to recover contaminated soils (phytoremediation) increases soil fungal diversity, in particular of ectomycorrhizal fungi. Restoring with different tree species, so forming a mixed forest, increases the spatial heterogeneity of environmental conditions; in consequence, the soil fungal biodiversity will be higher and the ecosystem services in the phytoremediated area will be promoted.

The study has been published in the journal Soil Biology and Biochemistry:

Gil-Martínez M, López-García Á, Domínguez MT, Kjøller R, Navarro-Fernández CM, Rosendahl S, Marañón T (2021). Soil fungal diversity and functionality are driven by plant species used in phytoremediation. Soil Biology and Biochemistry, 153: 108102.

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).

 

The assessment and evaluation of ecosystem services is a valuable tool to support and justify sustainble soil management.

Researchers of IRNAS, CSIC have contributed to the development of a methodology to quantify changes in ecosystem services induced by soil management measures, as part of the European RECARE consortium.

A comparative analysis of the results for 26 measures applied to remediate degraded soils, in 16 case studies across Europe, has been carried out. In particular, IRNAS´s researchers have evaluated the results of amendments (biosolid compost) and tree planting (wild olive) in contaminated and remediated soils of the Guadiamar Green Corridor.

The new methodology was applied to evaluate the impacts of each 26 measures on different ecosystem services. The most relevant 15 ecosystem services were selected, grouped in provisioning, regulation and cultural services. In general, the applied soil remediation measures produced positive changes in ecosystem services. Within the regulation services, “mediation of flows” (protection from erosion) and “mediation of waste, toxics and other nuisances” (stabilization of contaminants) showed the most important positive impacts.

The methodology also detected synergies and trade-offs among ecosystem services. This holistic approach may be the base for a valuation of the benefits from each ecosystem service and the integrated management of the evaluated land.

The results have been published in the December issue of the open access journal Sustainability:

Gudrun Schwilch, Tatenda Lemann, Örjan Berglund, Carlo Camarotto, Artemi Cerdà, Ioannis N. Daliakopoulos, Silvia Kohnová, Dominika Krzeminska, Teodoro Marañón, René Rietra, Grzegorz Siebielec, Johann Thorsson, Mark Tibbett, Sandra Valente, Hedwig van Delden, Jan van den Akker, Simone Verzandvoort, Nicoleta Olimpia Vrînceanu, Christos Zoumides, Rudi Hessel (2018), Assessing impacts of soil management measures on Ecosystem Services. Sustainability, 10 (12), 4416, doi:10.3390/su10124416.

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.