The rhizospheric microbial action, accelerating the degradation of compounds in the soil, is known as phytostimulation. It represents one of the main phytoremediation mechanisms in herbicide-contaminated soil. Tebuthiuron-tolerant plants, which are able to stimulate their rhizospheric microorganisms, could be highly interesting for the phytoremediation of this herbicide. This study aimed at evaluating the rhizospheric activity of four plant species with phytoremediation potential for tebuthiuron and to infer on the contribution of the roots to the process of decontamination of this herbicide. The rhizospheric soil of jackbean (Canavalia ensiformis), pearl millet (Pennisetum glaucum), Georgia velvet bean (Stizolobium deeringianum), and black velvet bean (Stizolobium aterrimum), plus a control treatment (without plant) were analyzed without and with tebuthiuron at 0.73 ìg g-1. The CO2 evolution rate was quantified 1, 2, 3 and 10 days after the treatment application. The herbicide treatments were submitted to contamination with 40 ìg g-1 tebuthiuron. After the application, the CO2 evolution rate was measured 1 and 50 days after the treatment applications, using a continuous flow respirometer. Compared to the other species and the control treatment, C. ensiformis presented the highest CO2 evolution rate throughout the experimental phase, followed by S. aterrimum at the commercial herbicide dose. Under higher herbicide concentrations, mean CO2 evolution rate values were higher in rhizospheric soil of C. ensiformis, followed by that from S. aterrimum and S. deeringianum. C. ensiformis presented the best performance, and except for this plant species, the rhizospheric contribution to the tebuthiuron phytoremediation at levels above the commercial dose was not relevant.
soil respiration; green manures; bioremediation; reclamation
