Effect of earthworms on plant Lantana camara Pb-uptake and on bacterial communities in root-adhering soil.

The present study aimed to assess the potential abilities of Lantana camara, an invasive plant species for phytoremediation in the presence of earthworm Pontoscolex corethrurus. Effects of earthworm on growth and lead (Pb) uptake by L. camara plant were studied in soil artificially contaminated at 500 or 1000mg of Pb kg(-1) soil. This species has a promising value for phytoremediation because it can uptake as much as 10% of 1000mgkg(-1) of Pb per year. Moreover, the presence of earthworms enhanced plant biomass by about 1.5-2 times and increased the uptake of lead by about 2-3 times. In the presence of earthworm, L. camara was thus able to uptake up 20% of Pb presence in the soil, corresponding to remediation time of 5 years if all organs are removed. As soil microorganisms are known to mediate many interactions between earthworms and plants, we documented the effect of earthworms on the bacterial community of root-adhering soil of L. camara. Cultivable bacterial biomass of root-adhering soil increased in the presence of earthworms. Similar trend was observed on bacterial metabolic activities. The increase of lead concentrations from 500 to 1000mgkg(-1) did not have any significant effect either on plant growth or on bacterial biomass and global activities but affected the structure and functional diversity of the bacterial community. These results showed that we should broaden the ecological context of phytoremediation by considering plant/microbial community/earthworm interactions that influence the absorption of heavy metals.