Dialing in remote measurements of grapevine water stress by incorporating whole plant physiological responses

Abstract

Context and purpose of the study. Current remote sensing strategies rely heavily on reflectance data and energy balance modelling using thermal imagery to estimate crop water use and stress. These approaches show great promise for driving precision management decisions but still require work to better understand how detected changes relate to meaningful physiological changes. Under water stress, grapevines exhibit a range of responses involving both biological and physical changes within leaves and canopies. This study aims to improve remote sensing indices to track grapevine stress by integrating both physical and biological effects from leaf to canopy and ultimately up to the vineyard level.

Material and methods. A two treatment drought experiment was conducted over the summer of 2024 within a field site in Davis, California spanning across two wine grape varieties (Cabernet Sauvignon and Chardonnay). Diurnal measurements taken at the site were intended to monitor drought stress within the canopy by looking at gas exchange and water movement within individual vines. Physiological measurements of upper and lower canopy levels were used to identify differences between leaves visible by drone and leaves that are not. LiDAR scans were also taken to monitor temporal changes of the canopy in response to water stress.

Results. This dataset can be used to answer questions about whole plant water stress, changes in leaf angle under water stress, where spectral signals are most useful in identifying plant stress, and if seasonal and diurnal changes impact spectral responses. Whole plant stress is integrated by looking at upper and lower canopy responses and compared to drone measurements as well as IRT wavelet calculations for each vine to determine best methods for spectral measurements of grapevine water stress.