Non-resonant air-coupled ultrasound for quantifying leaf hydration dynamics and turgor loss in potato leaves

[摘要] This study investigates the use of non-resonant air-coupled ultrasound technique as a non-destructive tool for quantifying leaf water status dynamics in potato (Solanum tuberosum) leaves. Conventional methods for measuring leaf water status, such as relative water content or pressure–volume (P–V) curves, are destructive and labor-intensive, whereas ultrasound can probe internal tissue structure through mechanical wave propagation. In this work, freshly detached potato leaves were gradually dehydrated under controlled laboratory conditions while ultrasonic transmission signals were recorded using broadband air-coupled transducers operating between 250 kHz and 900 kHz. Time-domain and frequency-domain features, including peak-to-peak amplitude, time-of-flight (ToF), spectral amplitude, and transmission coefficient, were extracted and analyzed as a function of relative water content (RWC). The normalized peak-to-peak (pk–pk) amplitude curve exhibited a clear correlation to the P–V curve, with ultrasonic turgor loss point (TLP) candidate (\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\mathrm {TLP_c}=0.973$$\end{document}) that closely matched the physiological turgor loss point (TLP) obtained from P–V analysis (\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\mathrm {RWC_{TLP}}=0.978$$\end{document}). ToF showed a characteristic biphasic response with a slight initial decrease at high RWC followed by a sharp decrease around the dehydration threshold (\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\mathrm {TLP_c} \approx 0.956$$\end{document}), reflecting the progressive loss of cell-wall tension and increasing mesophyll deformability that are expected to reduce acoustic velocity during dehydration. Spectral amplitude and transmission coefficient exhibited frequency-dependent sensitivity that peaked near 650 kHz. All ultrasonic parameters produced TLP candidates within 2.5% of the physiological reference, confirming that acoustic propagation is governed by turgor-driven structural transitions in the mesophyll. These results establish that non-resonant ultrasound technique can characterize water status in leaves that lack thickness resonances, extending the scope of ultrasonic hydration sensing beyond resonant techniques. The high physiological TLP observed for potato confirms that turgor is lost very early during dehydration, reflecting the species limited osmotic adjustment and drought sensitivity. The limitation of this study is that measurements were performed on detached leaves under controlled conditions; future in situ validation on intact plants under varying microclimates is required. Future work will also focus on deriving attenuation coefficients to separate intrinsic viscoelastic attenuation from absorption mechanisms. Overall in this study, pk–pk amplitude emerged as the most sensitive, computationally efficient, and practical parameter for real-time ultrasonic monitoring of leaf water status and early stress detection.

[发布日期] 2026-09-27