Photochemical Reflectance Index (PRI) for Detecting Responses of Diurnal and Seasonal Photosynthetic Activity to Experimental Drought and Warming in a Mediterranean Shrubland

Abstract

Climatic warming and drying are having profound impacts on terrestrial carbon cycling by altering plant physiological traits and photosynthetic processes, particularly for species in the semi-arid Mediterranean ecosystems. More effective methods of remote sensing are needed to accurately assess the physiological responses and seasonal photosynthetic activities of evergreen species to climate change. We evaluated the stand reflectance in parallel to the diurnal and seasonal changes in gas exchange, fluorescence and water contents of leaves and soil for a Mediterranean evergreen shrub, Erica multiflora, submitted to long-term experimental warming and drought. We also calculated a differential photochemical reflectance index (∆PRI, morning PRI subtracted from midday PRI) to assess the diurnal responses of photosynthesis (∆A) to warming and drought. The results indicated that the PRI, but not the normalized difference vegetation index (NDVI), was able to assess the seasonal changes of photosynthesis. Changes in water index (WI) were consistent with seasonal foliar water content (WC). In the warming treatment, ∆A value was higher than control in winter but ∆Yield was significantly lower in both summer and autumn, demonstrating the positive effect of the warming on the photosynthesis in winter and the negative effect in summer and autumn, i.e., increased photosynthetic midday depression in summer and autumn, when temperatures were much higher than in winter. Drought treatment increased the midday depression of photosynthesis in summer. Importantly, ∆PRI was significantly correlated with ∆A both under warming and drought, indicating the applicability of ∆PRI for tracking the midday depression of photosynthetic processes. Using PRI and ∆PRI to monitor the variability in photosynthesis could provide a simple method to remotely sense photosynthetic seasonality and midday depression in response to ongoing and future environmental stresses.

Characteristics of Water Physiological Integration and its Ecological Significance for Populus euphratica Young Ramets in an Extremely Drought Environment

“…The bimodal pattern of the water integration is identified as “midday depression” by previous researches and regarded as an important strategy of plants to cope with water deficit by decreasing the water consumption for transpiration (Gartner et al, ; Ma et al, ). A similar physiological phenomenon of midday depression was also found for the photosynthesis of P. euphratica and others species (Y. P. Chen et al, ; Jhou et al, ; Zhang et al, ).…”

Relation of Photochemical Reflectance Indices Based on Different Wavelengths to the Parameters of Light Reactions in Photosystems I and II in Pea Plants

“…There are numerous investigations that analyze the relations of the modifications of reflectance with the responses of physiological processes (including photosynthesis and its regulation [16][17][18][19][20], growth [21], water exchange [14,22,23], isoprene emission [20,24,25], electrical activity [26][27][28], etc. ), the changes in biochemical content (including concentrations of chlorophylls [29][30][31], carotenoids [32][33][34], nitrogen compositions [35,36], etc.…”

“…), the changes in biochemical content (including concentrations of chlorophylls [29][30][31], carotenoids [32][33][34], nitrogen compositions [35,36], etc. ), or the plant damage caused by abiotic [17,20] and biotic stressors [11,12,15]. The calculation of numerous reflectance indices, which are often based on measurements of changes in intensity of the reflected light at specific wavelengths in comparison with one at a reference wavelength, can strongly improve the analysis of plant reflectance [10,[13][14][15].…”

Potential of Photochemical Reflectance Index for Indicating Photochemistry and Light Use Efficiency in Leaves of European Beech and Norway Spruce Trees

“…The lower Chla+b/Carx+c in our study did not facilitate separating the effect of drought using PRI, but the higher carotenoid levels in HI-HT3 did increase the magnitude of ∆PRI in saplings stressed by high temperature and drought. Increased carotenoids levels provide higher capacity for dynamic NPQ, which generates larger amplitudes of ∆PRI under given conditions [79].…”