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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).