Surface Acoustic Waves to Drive Plant Transpiration

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

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.

In situ laser manipulation of root tissues in transparent soil

AIMS

Laser micromanipulation such as dissection or optical trapping enables remote physical modification of the activity of tissues, cells and organelles. To date, applications of laser manipulation to plant roots grown in soil have been limited. Here, we show laser manipulation can be applied in situ when plant roots are grown in transparent soil.

METHODS

We have developed a Q-switched laser manipulation and imaging instrument to perform controlled dissection of roots and to study light-induced root growth responses. We performed a detailed characterisation of the properties of the cutting beams through the soil, studying dissection and optical ablation. Furthermore, we also studied the use of low light doses to control the root elongation rate of lettuce seedlings (Lactuca sativa) in air, agar, gel and transparent soil.

RESULTS

We show that whilst soil inhomogeneities affect the thickness and circularity of the beam, those distortions are not inherently limiting. The ability to induce changes in root elongation or complete dissection of microscopic regions of the root is robust to substrate heterogeneity and microscopy set up and is maintained following the limited distortions induced by the transparent soil environment.

CONCLUSIONS

Our findings show that controlled in situ laser dissection of root tissues is possible with a simple and low-cost optical set-up. We also show that, in the absence of dissection, a reduced laser light power density can provide reversible control of root growth, achieving a precise "point and shoot" method for root manipulation.

Numerical emulation of Thru-Reflection-Line calibration for the de-embedding of Surface Acoustic Wave devices

In this contribution, a rigorous numerical calibration is proposed to characterize the excitation of propagating mechanical waves by interdigitated transducers (IDTs). The transition from IDT terminals to phonon waveguides is modeled by means of a general circuit representation that makes use of Scattering Matrix (SM) formalism. In particular, the three-step calibration approach called the Thru-Reflection-Line (TRL), that is a well-established technique in microwave engineering, has been successfully applied to emulate typical experimental conditions. The proposed procedure is suitable for the synthesis/optimization of surface-acoustic-wave (SAW) based devices: the TRL calibration allows to extract/de-embed the acoustic component, namely resonator or filter, from the outer IDT structure, regardless of complexity and size of the letter. We report, as a result, the hybrid scattering parameters of the IDT transition to a mechanical waveguide formed by a phononic crystal patterned on a piezoelectric AlN membrane, where the effect of a discontinuity from periodic to uniform mechanical waveguide is also characterized. In addition, to ensure the correctness of our numerical calculations, the proposed method has been validated by independent calculations.

Enhancement of plant leaf transpiration with effective use of surface acoustic waves: effect of wave frequency

Water transport in vascular plants provides remarkable opportunities for various engineering applications due to its highly efficient and powerless transportability. Several previous studies were conducted to regulate the biological responses of plants using noninvasive audible or ultrasound waves. However, the control mechanism of acoustic stimuli applied to plants has not been investigated yet. Thus, the practical application of these stimuli to real plants still exhibits technological limitations. This study experimentally investigated the effects of surface acoustic wave (SAW) frequency on plant transpiration to understand the acoustic-activated leaf transpiration and utilize the advantages of SAW. We captured consecutive images of the enhanced water transport in the test plant (Epipremnum aureum) by SAW at three different frequencies (10, 15, and 20 MHz). The dye solution at 15 MHz SAW presented the highest intensity value after 40 min of SAW stimulation. The excitation areas for 15 and 20 MHz SAWs were decreased to 42.3% and 22.6%, respectively, compared with that of 10 MHz SAW. The transpiration rates were directly measured to compare water transport enhancement quantitatively when different SAW frequencies were applied to the same plant leaves. The water transport in the leaves was maximized at 15 MHz SAW, regardless of excitation area.

Plant leaf transpiration was enhanced with effective use of SAW activation. The effects on leaf transpiration enhancement were analyzed in detail. The results could be applied to regulate temperature and relative humidity effectively.