07 Nov Poster at the 9th International Workshop on Chemical Bioavailability in the Terrestrial Environment
Title: “Improving phytostabilisation potential of poplar using biochar and plant growth-promoting bacterial inoculants”
Partners involved: IIAG-CSIC, INRA
Publication data: 9th International Workshop on Chemical Bioavailability in the Terrestrial Environment; 5th-8th November 2017, Warsaw, Polandpóster Pardo et al V3
The use of organic and/or inorganic amendments in phytostabilisation techniques is often essential for improving the soil physicochemical properties and fertility, in order to permit plant establishment and reduce contaminant dispersion. Amongst the various materials that can be used as amendments, recent years have seen growing interest in the benefits of biochar. Biochar results from the pyrolysis of organic materials in the total or partial absence of oxygen, and its production aims to generate energy or reduce waste volume. Due to its alkaline nature, high surface area and negatively charged functional groups, its application usually enhances soil cation exchange capacity and adsorbs positively charged metal ions (e.g. Cu2+). However, it can affect the availability of nutrients, and transiently increase soil salinity and dissolved organic matter. Therefore, the use of biochar in phytostabilisation processes could be optimized by combining it with the application of other materials (like composts) that can balance these negative effects. Moreover, inoculation of plants with plant growth-promoting bacteria (PGPB) can induce beneficial effects on plant growth, health and resistance to stress, as well as improving water absorption, increasing nutrient availability and contributing to pollutant stabilization in the soil through the excretion of complexing substances (polysaccharides, organic acids, siderophores, etc.). The combination of all these options may enable successful plant establishment in contaminated soils and improve the overall efficiency of the remediation process.
This study aimed at assessing the combined use of biochar (alone and mixed with composted sewage sludge) and inoculation with PGPB in the phytostabilisation of a copper (Cu) mine soil with poplar (Populus maximowiczii x Populus trichocarpa var. Skado). Plant biomass production, metal accumulation and oxidative stress in plant parts, as well as changes in soil properties and metal availability, were determined.
A factorial pot trial was established using mine tailings from the Touro Cu mine (NW Spain), characterised by a low pH (<3.0) and high metal concentrations (mean pseudo-total concentrations: 42.5 g Al kg-1; 596 mg Cu kg-1). The following soil treatments were set up: (i) untreated soil (UNT); (ii) soil with CaCO3 (at 1%; CA); (iii) soil treated with biochar and CaCO3 (at 2.5% and 1%, respectively; B-CA); (iv) soil treated with compost and CaCO3 (at 2% and 1%, respectively; CM-CA); (v) and soil with a combination of the three amendments (at 2.5%, 2% and 1%, respectively; B-CM-CA).
The amendment incorporation increased the soil pH from 3.0 to 4-4.8, and the B-CM-CA treatment was most efficient. The untreated soil presented high extractable concentrations of Al, Cu and Zn (1484±57, 86±4 and 92±6 mg kg-1, respectively). The amendment addition efficiently reduced the availability of these elements in soil, but no inoculation effect was observed. Available-Al, -Cu and -Zn concentrations were reduced by 94-99%, 91-99% and 69-92%, respectively. The effect of the amendment treatments on metal availability followed the decreasing order: B-CM-CA > CM-CA > B-CA > CA. Additionally, soil amendments increased the concentration of essential nutrients in the soil (Ca, K, and Mg).
Plants were not able to survive in untreated soil without any amendments. The addition of the biochar- and compost-based mixtures increased the number of leaves compared to plants growing in CA-soils, and the mixture of B-CM-CA significantly enhanced shoot and root biomasses. The inoculum effect on plant growth depended on the soil treatment, and was less evident when the soil received compost. Inoculation was especially effective in plants growing in B-CA-treated soils, where all strains increased the shoot biomass of poplar, and strain SK20.12 also increased root dry weight. Application of the amendment combinations successfully improved soil conditions, reduced metal availability and allowed poplar development. Bacterial inoculants did not enhance plant growth when compost was added to soil, but were beneficial when biochar was not combined with another type of organic matter.