Effects of earthworms on the fungal community and microbial activity in root-adhering soil of Lantana camara during phytoextraction of lead
Résumé
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. (C) 2015 Elsevier B.V. All rights reserved.