Phytostabilisation of trace elements with different tree species revealed a species-specific effect on soil functioning

Abstract

Phytostabilisation is the use of plants and associated microorganisms to reduce the mobility of soil contaminants. Its efficiency is highly dependent on plant identity because of species-specific effects on soils, which also affect soil nutrient cycling and microbial growth. In a trace element (As, Cd, Cu, Pb, Zn) contaminated soil in SW Spain, a long-term phytoremediation plan was implemented to reduce the spread of contaminants in the mine-spill affected area. Soils underneath three native tree species: white poplar (Populus alba), stone pine (Pinus pinea) and wild olive (Olea europaea), were sampled 15 years after plantation to evaluate medium-term soil functionality. A significant effect of tree species on soil contamination levels was not found. In relation to soil nutrients, afforested soils presented an increasing soil fertility in comparison to treeless soils. Among species, soils underneath white poplar presented a lower acidification and a higher N content, while soils underneath stone pine were acidified and showed the highest C:N ratio. Regarding soil microbial biomass, a significant effect of stone pine was found indicating a reduction on biomass. Tree species showed different effects depending on specific soil enzyme activities, however, in general, enzyme activities were highly driven by soil acidification and contamination. In conclusion, the medium-term effect of phytostabilisation by the studied tree species was weak in terms of contamination stabilisation, however a marked tree species footprint was found in terms of soil nutrient contents as well as on microbial biomass and enzyme activities. Therefore, a species-specific effect was found with direct consequences on soil functionality.