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 CO 2 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.

Responses and Differences in Tolerance to Water Shortage under Climatic Dryness Conditions in Seedlings from Quercus spp. and Andalusian Q. ilex Populations

“…The F v /F m parameter reflects the amount of light energy required for photosynthesis that is used as a parameter of response to drought stress and tolerance as different studies have revealed [60,61]. As expected, irrigated seedlings showed optimal values for different plant species of around 0.83 [62].…”

Drone‐based physiological index reveals long‐term acclimation and drought stress responses in trees

“…Studies also seem to suggest that PRI measurements can determine post‐drought recovery not only in terms of water status but also in terms of photosynthetic capacity, better than other parameters commonly used to assess plant water relations, such as leaf or stem water potential. PRI has been shown to track CO 2 net assimilation rates recovering simultaneously with water status (Peguero‐Pina et al, 2008 ) but also the impairment of photosynthetic capacity that persisted despite the recovery of water status (Sancho‐Knapik, Mendoza‐Herrer, Gil‐Pelegrín, & Peguero‐Pina, 2018 ). However, most of this evidence comes from short‐term (e.g., 1 month or one growing season) drought experiments in seedlings or orchard ecosystems (Marino et al, 2014 ; Peguero‐Pina et al, 2008 ; Sancho‐Knapik et al, 2018 ; Zarco‐Tejada et al, 2012 ), where the drought response is exclusively driven by concurrent environmental conditions.…”

Phenotyping Plant Responses to Biotic Stress by Chlorophyll Fluorescence Imaging

“…The capacity for energy dissipation at the PSII could also be estimated by several VIs across plant species. NPQ and the de-epoxidation state of the xanthophyll cycle (which controls NPQ) correlate negatively with PRI at canopy (Gamon et al, 1992) and leaf scale (Gamon et al, 1997; Van Gaalen et al, 2007; Rahimzadeh-Bajgiran et al, 2012; Alonso et al, 2017; Sancho-Knapik et al, 2018). More recently, the indices ΔPRI (which accounts for pigment composition in PRI) and the normalized difference spectral index (NDSI) were reported to estimate NPQ more accurately than PRI (Maimaitiyiming et al, 2017; Kováč et al, 2018).…”