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Trees and soil fungal diversity

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.

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