Plant and soil microbial community responses to solid waste leachates diffusion on grassland

This work aims to define the effect on soil-plant relationships and soil quality of adding leachates from municipal solid waste incinerator (MSWI) ashes on recipient experimental grasslands. Leachates from MSWI-bottom ashes (BA) and MSWI-solidified air pollution control residues (SAPCr) contained a large content of salts and may be a source of an important disturbance of biological functioning of soils or grassland in the neighbourhood of systems containing such residues. Leachates obtained from solid waste were spread on field experimental plots with indigenous grasses (herbaceous fallow) or with introduced vegetation (seedlings of an indigenous colonial bentgrass: Agrostis tenuis). After the spreading of leachates, some effects on vegetation (at day 180 and day 480) and on bacteria communities of soil (at day 90 and at day 480) were assessed. On soil, a significant increasing of Na+ percentage of the exchange complex (ESP) was observed. The colonial bentgrass was found to be more sensitive to BA phytotoxicity than indigenous grasses, with a decrease of root (43%) and aerial (29%) biomass 180 days following the contamination. Conversely, a positive effect on the biomass was observed following the addition of SAPCr leachate. The use of a molecular tool to assess the effects on soil eubacteria community (A-RISA) showed a significant large modification of the community structure with SAPCr leachate, when a low effect was observed with BA. Grass cover and root influence on the behaviour of the bacterial communities with respect to the leachates were shown.