Canopy observations of a table grape vineyard: Radiation balance, energy partitioning and CO2 fluxes

The relationship between spectral light reflectance and leaf water content has been established for several species, giving a sound basis to the use of remote sensing technologies in water stress detection for natural vegetation and crops. Nevertheless, few data are available about fruit tree species. The leaf and canopy reflectance features as indicators of plant water status have been here investigated in apple trees cv Golden Delicious grown in pots under progressive water stress. While the reflectance in the visible wavelengths was stable, some increase in this optical signature was observed in the 900-1000 nm spectral band when relative water content (RWC) decreased from 90.4% to 85.4%. This last RWC corresponded to a noticeable plant stress evidenced by photosynthesis and water potential trends. The depletion in reflectance in the whole 900-1000 waveband dramatically increased when further decreases in RWC up to 40.6% were reached in detached leaves, highlighting the absorption rule of water in the near-infrared region. On the contrary, the information about a decreasing leaf water content and the occurring of stress status was not inferred by the whole-canopy spectral reflectance measurements.