Effects of earthworms on the fungal community and microbial activity in root-adhering soil of Lantana camara during phytoextraction of lead

Earthworms are known to stimulate soil microorganisms and to enhance phytoextraction of metals. This study was designed to test the hypothesis that the positive effect of earthworms on phytoextraction performance results from the stimulation of soil fungi that are known to be tolerant to heavy metals in contaminated soils. It set out to assess the relationships between lead phytoextraction and the changes in soil fungi in response to earthworm activity. The experiment was performed in outdoor microcosms combining: earthworms (Pontoscolex corethrurus), Spanish Flag (Lantana camara) and soil spiked with 500 and 1000 mg Pb kg(-1). Cultivable fungi were enumerated using plate counts. PCR-DGGE analysis targeting the 28S rRNA gene was used to determine the structure of the fungal community. Total microbial activity was measured by fluorescein diacetate (FDA) hydrolysis assay. Plant Pb uptake by L. camara increased by about 2.5-fold in the presence of earthworms, regardless of the Pb concentration. This was significantly correlated with the increase in total microbial activity, abundance of cultivable fungi and richness index of the fungal community calculated from DGGE banding patterns. In the presence of earthworms, there was a significant positive correlation between microbial activity, plant biomass and plant Pb uptake. There was no correlation for the control without earthworms. These results provide evidence that interactions between earthworms and soil microorganisms have a positive effect on Pb-phytoextraction yield. The study of the ecological context of phytoremediation should be broadened by considering the interactions between plants, microorganisms and earthworms that affect heavy metal uptake by plants

Improvement of the phytoremediation efficiency of Neyraudia reynaudiana for lead-zinc mine-contaminated soil under the interactive effect of earthworms and EDTA

Abstract Slow plant growth, low biomass, and low bioavailability of heavy metals in soil are important factors that limit remediation efficiencies. This study adopted a pot cultivation method to evaluate the phytoremediation efficiency of Neyraudia reynaudiana, planted in contaminated soil from a lead-zinc mining area. The soil was inoculated with earthworms (Eisenia fetida), and mixed with the chelating agent ethylenediaminetetraacetic acid (EDTA) one month after planting. The addition of earthworms significantly increased the aboveground biomass of N. reynaudiana and activated heavy metals in the soil, thus facilitating heavy metal uptake by N. reynaudiana. The addition of EDTA significantly increased the incorporation and transport of heavy metals, reduced the uptake of heavy metals by the plant cell wall, and increased the proportions of cellular soluble constituents. Especially with regard to lead, inoculation with earthworms and EDTA application significantly promoted the accumulation efficiency of N. reynaudiana, increasing it 7.1-16.9-fold compared to the control treatment without earthworms and EDTA, and 1.5-2.3-fold compared to a treatment that only used EDTA

Influence of earthworm bioturbation on metals phytoavailability and human gastric bioaccessibility.

International audienceAt the global scale, urban agriculture is increasingly developing in cities due to demographic growth and sustainable food concerns. But, urban soils are frequently polluted with metals. In urban gardens, organic matter is also commonly added both to valorize organic household waste and to promote biophysicochemical fertility. As earthworms promote the decomposition and the recycling of soil organic matter, they can also influence the biogeochemical cycle of metals in urban polluted soils. In order to produce safe vegetables in urban areas, it is crucial to highlight the mechanisms involved in complex soil-earthworm-plant ecosystems. An experiment was set up to examine these relationships using lettuce cultivated in controlled conditions with RHIZOtest® devices. Thanks to the RHIZOtest® devices, metal transfer and bioaccessibility were for the first time compared for urban polluted soil without (1-urban soil polluted with Pb, Cd, Cu, and Zn: essential or toxic metals currently found in environment, SNB) and with bioturbation (2-this metal-polluted soil subjected to earthworm bioturbation, SB) and earthworm casts (3-earthworm casts produced in this polluted soil and naturally enriched in organic matter and microorganisms, T). Metal concentration, phytoavailability, and human gastric bioaccessibility were determined in the different samples. Results showed that earthworm bioturbation increased the phytoavailability of all the metals. For the experimental condition SB, the phytoavailability of metals was increased up to 75% compared to SNB. In addition, surprisingly, metal phytoavailability was always superior in SB compared to earthworm casts (T). Moreover, earthworms led to an increase in Zn gastric bioaccessibility up to 10% in the soils in the same way as for phytoavailability, meaning Zn bioaccessibility in SB > T > SNB, whereas it remained unchanged in the lettuces. These data are important to promote sustainable agriculture activities in urban areas; actually, databases concerning different experimental conditions are needed to develop decision support tools