Enhancement of the Cd phytoremediation efficiency of Festuca arundinacea by sonic seed treatment

Abstract

It has been reported that both naturally occurring and artificially created sounds can alter the physiological parameters of various plants. A series of experiments were designed in the present study to estimate the physiological responses and the variation in the Cd decontamination capacity of Festuca arundinacea under sonic wave treatments. Plant seeds were treated by sound waves of frequency 200, 300, 400, 500, and 1000 Hz, and the germinated seedlings were transplanted to Cd-polluted soil. The results showed that all the sonic treatments increased the whole plant dry weight of F. arundinacea compared with that of the control, and the highest value was observed in the 200 Hz treatment. The Cd content in below-ground and aerial tissues of the species increased with increasing frequency till 400 Hz, after which they became constant. A higher proportion of senescent and dead leaf tissues was observed in the high-frequency treatment (1000 Hz), and more Cd was transferred to these failing tissues. Therefore, in the 1000 Hz treatment, a significantly greater amount of Cd could be eliminated by harvesting the senescent and dead leaf tissues of the species compared with that of the other treatments. The concentrations of dissolved organic matter (DOM) and the proportions of hydrophilic fractions which have a strong Cd affinity, in the rhizosphere soil of F. arundinacea increased with the increase in sound frequency. Cd extraction ability of DOM also increased with increasing frequency. This study indicated that a suitable sonic treatment can improve the phytoextraction efficiency of F. arundinacea, and also explained the mechanism from the perspective of the variations in soil DOM.