Combining Sun-Induced Chlorophyll Fluorescence and Photochemical Reflectance Index Improves Diurnal Modeling of Gross Primary Productivity

Abstract

Sun-induced chlorophyll fluorescence (F) is a novel remote sensing parameter providing an estimate of actual photosynthetic rates. A combination of this new observable and Monteith's light use efficiency (LUE) concept was suggested for an advanced modeling of gross primary productivity (GPP). In this demonstration study, we evaluate the potential of both F and the more commonly used photochemical reflectance index (PRI) to approximate the LUE term in Monteith's equation and eventually improve the forward modeling of GPP diurnals. Both F and the PRI were derived from ground and airborne based spectrometer measurements over two different crops. We demonstrate that approximating dynamic changes of LUE using F and PRI significantly improves the forward modeling of GPP diurnals. Especially in sugar beet, a changing photosynthetic efficiency during the day was traceable with F and incorporating F in the forward modeling significantly improved the estimation of GPP. Airborne data were projected to produce F and PRI maps for winter wheat and sugar beet fields over the course of one day. We detected a significant variability of both, F and the PRI within one field and particularly between fields. The variability of F and PRI was higher in sugar beet, which also showed a physiological down-regulation of leaf photosynthesis. Our results underline the potential of F to serve as a superior indicator for the actual efficiency of the photosynthetic machinery, which is linked to physiological responses of vegetation.

Surface Reflectance and Sun-Induced Fluorescence Spectroscopy Measurements Using a Small Hyperspectral UAS

“…These indicators, related to vegetation energy dissipation pathways, are characterized by strong diurnal and seasonal dynamics [48][49][50]. UASs, equipped with calibrated spectrometers, could provide accurate retrieval of PRI and SIF with the necessary temporal and spatial resolution towards vegetation stress detection and modeling of gross primary productivity [51][52][53][54].…”

The 2013 FLEX—US Airborne Campaign at the Parker Tract Loblolly Pine Plantation in North Carolina, USA

“…Together, the PRI and F685 were diagnostic for expression of physiologic down-regulation of photosynthesis in this forest ( Figure 14B). The PRI has been identified as a superior spectral index for discriminating and tracking plant stress [47][48][49][50][51][52]. The combined use of PRI and fluorescence has previously been proven to be advantageous for plant stress detection [32,[47][48][49][50][51][52].…”

“…The PRI has been identified as a superior spectral index for discriminating and tracking plant stress [47][48][49][50][51][52]. The combined use of PRI and fluorescence has previously been proven to be advantageous for plant stress detection [32,[47][48][49][50][51][52]. We also note the recently reported [53] success in relating PRI (MODIS PRI, computed from bands of the Moderate Resolution Imaging Spectrometer on the Terra and Aqua satellites) to forest LUE using morning and afternoon observations from MODIS Terra and Aqua satellites at four coniferous and mixed forest sites in Canada.…”

Do Daily and Seasonal Trends in Leaf Solar Induced Fluorescence Reflect Changes in Photosynthesis, Growth or Light Exposure?

“…For instance, the photochemical reflectance index (PRI), which responds to changes in violaxanthin pigment de-epoxidation status (DEPS) [15], has potential to approximate information about NPQ. When combined with information from greenness optical indices, such as the normalized difference vegetation index (NDVI) [16], photosynthesis and consequently gross primary production (GPP) can be modelled at global scales [10,14,[17][18][19]. However, how these spectral indices are related to photochemistry, NPQ and SIF cannot be examined at large spatial scales because direct measurements of photochemistry and NPQ are unfeasible.…”