Chl fluorescence parameters and leaf reflectance indices allow monitoring changes in the physiological status of Quercus ilex L. under progressive water deficit

Abstract

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 forest 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 solve this problem, we have evaluated the Quercus ilex L. water and photosynthetic status throughout an intense water scarcity event and a subsequent re-watering. Photosynthetic status 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 to use PRI to detect the level of photosynthetic activity in Q, ilex, as it is much easier-to-handle. We also concluded that intense droughts and heat stress not only might reduce photosynthetic status through changes in Chl fluorescence parameters during the stress period, but also might affect photosynthetic status once the plant water status is recovered