Unveiling a hidden link: does time hold the key to altered spectral signatures of grapevines under drought?

Remote sensing technology captures spectral data beyond the visible range, making it useful for monitoring plant stress. Vis-NIR (Visible-Near Infrared) spectroscopy (400-1000 nm) is commonly used to indirectly assess plant status during drought. One example is the widespread use of normalized difference vegetation index (NDVI) that is strongly linked to green biomass. However, a knowledge gap exists regarding the applicability of this method to all the drought conditions and if it is a direct correlation to the water status of the plant.

This study focused on the spectral behavior and physiological changes in leaves of two grapevine cultivars, Riesling and Pinot Noir, that were subjected to different dehydration conditions. Dehydration rates varied from quick to medium and slow, examining the effect of time on the spectral and physiological response. The goal was to determine the potential role of time influencing the consistency of responses across different water dehydration conditions, and if drought stress symptoms could be detected through Vis-NIR analysis. The experimental design included four dehydration treatments: leaf dehydration by (i) detaching the leaves, (ii) cutting the stem from the roots, (iii) removing the soil from the root zone, and (iv) natural dehydration by irrigation withholding. By monitoring the spectral and physiological changes, the study aimed to assess the impact of different dehydration timings and the detectability of associated symptoms. Our results suggest that the timing of dehydration strongly influences the spectral signature changes. In instances under comparable water potentials, plants subjected to fast dehydration (e.g., stem cutting or detached leaves) displayed spectral patterns not significantly different as compared to the ones from adequately hydrated control plants. In contrast, plants undergoing gradual dehydration over several days (e.g., via irrigation withholding) exhibited spectral modifications consistent with previously documented findings.

Acknowledgements: Supported by the Projects DigiPlant and ImStress funded by NÖ Forschungs- und Bildungsges.mbH (NFB), Neue Herrengasse 10, 3rd floor, 3100 St. Pölten, Austria. We sincerely thank Rudi Rizzoli and Soma Laszlo Tarnay for their valuable contributions to the plants management, which played a crucial role in the research project.