Solid vermicompost and liquid vermicompost leachate have contrasting impacts on cadmium, lead and zinc phytoextraction by the Syrian beancaper Zygophyllum fabago L.

Background and aims

Vermicompost is a valuable amendment for phytomanagement of heavy metals contaminated areas but its impact on plant physiology remains poorly documented. It is available in liquid or solid forms, but these forms were never compared for their influence on pollutant accumulation by the plant in relation to soil heavy metals bioavailabilities.

Methods

Solid vermicompost (SV) and liquid vermicompost leachate (LVL) were tested on spiked soils in the absence (control) or in the presence of either 10 mg.Kg⁻¹ Cd, 250 mg.Kg⁻¹ Zn or 500 mg.Kg⁻¹ Pb and cultivated with Zygophyllum fabago L. in a column device allowing leachate recovery and analysis. Plant physiological parameters were determined during 10 weeks of culture.

Results

SV reduced soil heavy metals bioavailability, improved plant growth and photosynthesis and reduced heavy metals concentrations in all organs. In contrast, LVL increased heavy metal bioavailability and root growth but inhibited shoot growth. LVL decreased root heavy metals concentrations but increased them in the shoots. Both types of amendments increased the total amount of heavy metal removed by the plant. Among the removed Cd and Zn less than 5% were removed by leaching and SV contributed to reduce percolation. SV contributed to stress avoidance by reducing pollutant uptake while LVL contributed to stress tolerance through reinforcement of endogenous protecting mechanisms.

Conclusions

Both SV and LVL are beneficial amendments for phytostabilization and phytoextraction of heavy metals by Z. fabago but act through distinct mechanisms on the plant in relation to mineral nutrition, oxidative stress and osmotic adjustment.