Affecting Factors and Recent Improvements of the Photochemical Reflectance Index (PRI) for Remotely Sensing Foliar, Canopy and Ecosystemic Radiation-Use Efficiencies

Abstract

Accurately assessing terrestrial gross primary productivity (GPP) is crucial for characterizing the climate-carbon cycle. Remotely sensing the photochemical reflectance index (PRI) across vegetation functional types and spatiotemporal scales has received increasing attention for monitoring photosynthetic performance and simulating GPP over the last two decades. The factors confounding PRI variation, especially on long timescales, however, require the improvement of PRI understanding to generalize its use for estimating carbon uptake. In this review, we summarize the most recent publications that have reported the factors affecting PRI variation across diurnal and seasonal scales at foliar, canopy and ecosystemic levels; synthesize the reported correlations between PRI and ecophysiological variables, particularly with radiation-use efficiency (RUE) and net carbon uptake; and analyze the improvements in PRI implementation. Long-term variation of PRI could be attributed to changes in the size of constitutive pigment pools instead of xanthophyll de-epoxidation, which controls the facultative short-term changes in PRI. Structural changes at canopy and ecosystemic levels can also affect PRI variation. Our review of the scientific literature on PRI suggests that PRI is a good proxy of photosynthetic efficiency at different spatial and temporal scales. Correcting PRI by decreasing the influence of physical or physiological factors on PRI greatly strengthens the relationships between PRI and RUE and GPP. Combining PRI with solar-induced fluorescence (SIF) and optical indices for green biomass offers additional prospects.

Connection of the Photochemical Reflectance Index (PRI) with the Photosystem II Quantum Yield and Nonphotochemical Quenching Can Be Dependent on Variations of Photosynthetic Parameters among Investigated Plants: A Meta-Analysis

“…Data that were registered by satellites were not used in the analysis. It should be noted that leaves and canopy levels are widely used scales of PRI measurements [15,61]. Measurements of PRI in leaves are often based on the application of spectrometers and specific systems of PRI measurement (e.g., PlantPen PRI 200) or systems of PRI imaging [15,61].…”

“…A meta-analysis of literature data seems to be an effective method for finding a solution to this problem. There are several works [15,61] that are devoted to the meta-analysis of results of PRI measurements. In particular, these works investigated the influence of different spatial scales (leaves, canopy, or ecosystem) and time scales (daily or seasonal) of PRI measurements on photosynthetic parameters.…”

“…Early monitoring of these damages plays an important role in precision agriculture and ecological monitoring. As a result, remote sensing of the photosynthetic process is an important practical problem [13][14][15]. There are many methods that can be used for the analysis of the photosynthesis process in plants; in particular, pulse-amplitude-modulation (PAM)-fluorometry [16,17], JIP-test [18][19][20], and analysis of CO 2 exchange [21][22][23][24][25].…”

“…In particular, these works investigated the influence of different spatial scales (leaves, canopy, or ecosystem) and time scales (daily or seasonal) of PRI measurements on photosynthetic parameters. A determination coefficient (R 2 ) was used in the works [15,61] as the quantitative criterion for the description of the relationship between physiological processes and the photochemical reflectance index. However, these studies, which were the basis of the meta-analysis, used different regression curves (e.g., linear, logarithmic, or exponential functions), making their comparison with using R 2 more difficult.…”

Plant ecophysiological responses to drought, nocturnal warming and variable climate in the Pannonian sand forest-steppe: results of a six-year climate manipulation experiment

“…Similar relationships with PRI also appeared for stomatal conductance and the actual photochemical efficiency of PSII (ΦPSII, qP and/or Fv'/Fm') for F. vaginata and P. alba. Such correlations might reflect coordinated regulation of the capacity for CO2 fixation with changes in environmental conditions, as found in other studies at different timescales and plant functional types (Peñuelas et al 1995, Stylinski et al 2002, Weng et al 2006, Zhang et al 2016. PRI negatively correlated with Fv/Fmdawn in C. dactylon and P. alba, and with E and gs in F. vaginata and P. alba, which might have also contributed to this regulation.…”