Continuous Proximal Monitoring of the Diameter Variation from Root to Fruit

Proximal plant-based monitoring provides high-resolution data about trees, leading to more precise orchard management and in-depth knowledge about the tree physiology. The present work focuses on continuous real-time monitoring of olive cv. 'Ascolana Tenera' on an hourly time span during the third stage of fruit growth (mesocarp cell expansion) under mild water stress conditions (ψStem above -2 MPa). This is achieved by mounting dendrometers on the root, trunk, branch, and fruit to assess and model the behavior of each organ. The diameter variation of each organ at various time intervals (daily, two-weeks, and entire experiment), as well as their hysteretic patterns relative to each other and vapor pressure deficit, has been demonstrated. The results show different correlations between various organs, ranging from very weak to strongly positive. However, the trend of fruit versus root consistently shows a strong positive relationship throughout the entire experiment (R² = 0.83) and good across various two-week intervals (R² ranging from 0.54 to 0.93). Additionally, different time lags in dehydration and rehydration between organs were observed, suggesting that the branch is the most reactive organ, regulating dehydration and rehydration in the tree. Regarding the hysteretic pattern, different rotational patterns and characteristics (shape) were observed among the organs and in relation to vapor pressure deficit. This research provides valuable insight into the flow dynamics within a tree, models plant water relations and time lags in terms of water storage and transport and could be implemented for precise olive tree water status detection.