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.