Chl Fluorescence Parameters and Leaf Reflectance Indices Allow Monitoring Changes in the Physiological Status of Quercus ilex L. under Progressive Water Deficit

Extreme droughts and heat events, frequently produced in Mediterranean climates, induce anomalies in the ecosystem–atmosphere CO2 fluxes. In order to mitigate the consequences on forests and agriculture, managers must have a better knowledge of the ecosystem by monitoring plant status. Water status is commonly observed measuring water potential but when the extreme event is over, this parameter cannot show managers the recovery of other physiological processes such as photosynthesis. To address this problem, we have evaluated the Quercus ilex L. water status and photosynthetic capacity throughout an intense water scarcity event and a subsequent re-watering. Photosynthetic capacity was evaluated through chlorophyll fluorescence parameters and leaf reflectance indices. We found that all fluorescence parameters changed as water potential decreased and they did not completely recover after re-watering. Among the reflectance indices, the physiological reflectance index (PRI) varied similarly to fluorescence, obtaining a strong correlation with the non-photochemical quenching (NPQ). We proposed using PRI to detect the level of photosynthetic capacity in Q. ilex, as it is much easier-to-handle. We also concluded that intense droughts and heat stress not only might reduce photosynthetic capacity through changes in Chl fluorescence parameters during the stress period, but might also affect photosynthetic capacity once the plant water status is recovered