Exploring the scattering and reabsorption of chlorophyll fluorescence: implications for remote sensing of photosynthesis

2020 ◽  
Author(s):  
Karolina Sakowska ◽  
Maria Pilar Cendrero-Mateo* ◽  
Christiaan van der Tol ◽  
Marco Celesti ◽  
Giorgio Alberti ◽  
...  
Keyword(s):  
Chlorophyll Fluorescence ◽  
Heat Dissipation ◽  
Structural Parameters ◽  
Vegetation Indices ◽  
Field Measurements ◽  
Photosynthetic Performance ◽  
Photochemical Quenching ◽  
Spectral Vegetation Indices ◽  
Leaf Level ◽  
Scope Model

<p>In recent years, technological progress in high-resolution field spectrometers have enabled the use of alternative tracer for constraining ecosystem-scale photosynthesis, i.e. sun-induced fluorescence (SIF). The principle underlying the use of SIF as a proxy of gross primary productivity (GPP) is based on the fact that the light energy absorbed by chlorophyll molecules can proceed into three different pathways: photochemistry, heat dissipation, and chlorophyll fluorescence. Since these processes directly compete for the same excitation energy, measurements of SIF and non-photochemical quenching (NPQ) are expected to provide information on photosynthetic performance.</p><p>However, SIF signal measured at the leaf level or beyond is affected by several processes, including wavelength dependent scattering and reabsorption, which may need to be considered when linking SIF data and photosynthetic CO<sub>2</sub> assimilation.</p><p>To address this question, we conducted a multi-scale and multi-technique study that considered measurements of photosynthetic (GPP), optical (SIF, reflectance - R and transmittance - T), physiological (NPQ) and biophysical (the amount of absorbed photosynthetically active radiation - APAR) parameters of two soybean varieties: the MinnGold mutant, characterized by significantly reduced chlorophyll content (Chl), and the wild type, non-Chl deficient Eiko. We further used the “Soil-Canopy Observation Photosynthesis and Energy fluxes” (SCOPE) model to investigate the reabsorption and scattering of SIF. The measured leaf R, T and SIF and top-of-the-canopy R were used to retrieve biochemical and structural parameters of both varieties by inversion of the SCOPE model, while its forward mode was used to determine and correct for the scattering and reabsorption of SIF at both leaf and canopy level.</p><p>Our study revealed that despite the large difference in Chl content (the ratio of Chl between MinnGold and Eiko was nearly 1:5), similar leaf and canopy photosynthesis rates were maintained in the Chl‐deficient mutant. This phenomenon was captured neither by traditional spectral vegetation indices related to canopy greenness, nor by SIF measured in-situ. However, the modelling simulations revealed that when correcting for leaf and canopy scattering and reabsorption processes both varieties presented similar SIF yield (SIF/APAR). Furthermore, field measurements showed that APAR and NPQ in MinnGold were lower than in Eiko. This together explains the similar measured GPP and simulated SIF yield between the two varieties, and indicates that interpretation and application of SIF as a GPP tracer requires understanding and quantification of all these processes.</p>

scholarly journals Nonlinear Relationship Between the Yield of Solar-Induced Chlorophyll Fluorescence and Photosynthetic Efficiency in Senescent Crops

2020 ◽  
Vol 12 (9) ◽  
pp. 1518
Author(s):  
Leizhen Liu ◽  
Wenhui Zhao ◽  
Qiu Shen ◽  
Jianjun Wu ◽  
Yanguo Teng ◽  
...  
Keyword(s):  
Chlorophyll Fluorescence ◽  
Imaging System ◽  
Field Measurements ◽  
Maximum Efficiency ◽  
Operating Efficiency ◽  
Nonlinear Relationship ◽  
Diurnal Changes ◽  
Psii Photochemistry ◽  
Leaf Level ◽  
The Relationship

It has been demonstrated that solar-induced chlorophyll fluorescence (SIF) is linearly related to the primary production of photosynthesis (GPP) in various ecosystems. However, it is unknown whether such linear relationships have been established in senescent crops. SIF and GPP can be expressed as the products of absorbed photosynthetically active radiation (APAR) with the SIF yield and photosystem II (PSII) operating efficiency, respectively. Thus, the relationship between SIF and GPP can be represented by the relationship between the SIF yield and PSII operating efficiency when the APAR has the same value. Therefore, we analyzed the relationship between the SIF yield and the PSII operating efficiency to address the abovementioned question. Here, diurnal measurements of the canopy SIF (760 nm, F760) of soybean and sweet potato were manually measured and used to calculate the SIF yield. The PSII operating efficiency was calculated from measurements of the chlorophyll fluorescence at the leaf level using the FluorImager chlorophyll fluorescence imaging system. Meanwhile, field measurements of the gas exchange and other physiological parameters were also performed using commercial-grade devices. The results showed that the SIF yield was not linearly related to the PSII operating efficiency at the diurnal scale, reflecting the nonlinear relationship between SIF and GPP. This nonlinear relationship mainly resulted from the heterogeneity and diurnal dynamics of the PSII operating efficiency and from the intrinsic diurnal changes in the maximum efficiency of the PSII photochemistry and the proportion of opened PSII centers. Intensifying respiration was another factor that complicated the response of photosynthesis to the variation in environmental conditions and negatively impacted the relationship between the SIF yield and the PSII operating efficiency. The nonlinear relationship between the SIF yield and PSII efficiency might yield errors in the estimation of GPP using the SIF measurements of senescent crops.

scholarly journals Remote sensing of LAI, chlorophyll and leaf nitrogen pools of crop- and grasslands in five European landscapes

2013 ◽  
Vol 10 (10) ◽  
pp. 6279-6307 ◽  
Author(s):  
E. Boegh ◽  
R. Houborg ◽  
J. Bienkowski ◽  
C. F. Braban ◽  
T. Dalgaard ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Field Data ◽  
Vegetation Index ◽  
Normalized Difference Vegetation Index ◽  
Vegetation Indices ◽  
Field Measurements ◽  
Leaf Nitrogen ◽  
Agricultural Landscapes ◽  
Nitrogen Pools ◽  
Spectral Vegetation Indices

Abstract. Leaf nitrogen and leaf surface area influence the exchange of gases between terrestrial ecosystems and the atmosphere, and play a significant role in the global cycles of carbon, nitrogen and water. The purpose of this study is to use field-based and satellite remote-sensing-based methods to assess leaf nitrogen pools in five diverse European agricultural landscapes located in Denmark, Scotland (United Kingdom), Poland, the Netherlands and Italy. REGFLEC (REGularized canopy reFLECtance) is an advanced image-based inverse canopy radiative transfer modelling system which has shown proficiency for regional mapping of leaf area index (LAI) and leaf chlorophyll (CHLl) using remote sensing data. In this study, high spatial resolution (10–20 m) remote sensing images acquired from the multispectral sensors aboard the SPOT (Satellite For Observation of Earth) satellites were used to assess the capability of REGFLEC for mapping spatial variations in LAI, CHLland the relation to leaf nitrogen (Nl) data in five diverse European agricultural landscapes. REGFLEC is based on physical laws and includes an automatic model parameterization scheme which makes the tool independent of field data for model calibration. In this study, REGFLEC performance was evaluated using LAI measurements and non-destructive measurements (using a SPAD meter) of leaf-scale CHLl and Nl concentrations in 93 fields representing crop- and grasslands of the five landscapes. Furthermore, empirical relationships between field measurements (LAI, CHLl and Nl and five spectral vegetation indices (the Normalized Difference Vegetation Index, the Simple Ratio, the Enhanced Vegetation Index-2, the Green Normalized Difference Vegetation Index, and the green chlorophyll index) were used to assess field data coherence and to serve as a comparison basis for assessing REGFLEC model performance. The field measurements showed strong vertical CHLl gradient profiles in 26% of fields which affected REGFLEC performance as well as the relationships between spectral vegetation indices (SVIs) and field measurements. When the range of surface types increased, the REGFLEC results were in better agreement with field data than the empirical SVI regression models. Selecting only homogeneous canopies with uniform CHLl distributions as reference data for evaluation, REGFLEC was able to explain 69% of LAI observations (rmse = 0.76), 46% of measured canopy chlorophyll contents (rmse = 719 mg m−2) and 51% of measured canopy nitrogen contents (rmse = 2.7 g m−2). Better results were obtained for individual landscapes, except for Italy, where REGFLEC performed poorly due to a lack of dense vegetation canopies at the time of satellite recording. Presence of vegetation is needed to parameterize the REGFLEC model. Combining REGFLEC- and SVI-based model results to minimize errors for a "snap-shot" assessment of total leaf nitrogen pools in the five landscapes, results varied from 0.6 to 4.0 t km−2. Differences in leaf nitrogen pools between landscapes are attributed to seasonal variations, extents of agricultural area, species variations, and spatial variations in nutrient availability. In order to facilitate a substantial assessment of variations in Nl pools and their relation to landscape based nitrogen and carbon cycling processes, time series of satellite data are needed. The upcoming Sentinel-2 satellite mission will provide new multiple narrowband data opportunities at high spatio-temporal resolution which are expected to further improve remote sensing capabilities for mapping LAI, CHLl and Nl.

scholarly journals Combined chlorophyll fluorescence techniques to study environmental impact on the mountain moss Polytrichum commune

2021 ◽  
Vol 11 (1) ◽  
pp. 161-173
Author(s):  
Gabriella Nora Maria Giudici
Keyword(s):  
Chlorophyll Fluorescence ◽  
Conformational Changes ◽  
Heat Dissipation ◽  
Fluorescence Induction ◽  
High Light ◽  
Chlorophyll Fluorescence Induction ◽  
Photochemical Quenching ◽  
Light Harvesting Complexes ◽  
Polytrichum Commune ◽  
Non Photochemical Quenching

Two chlorophyll fluorescence (ChlF) methods were used to study the effects of high light (photoinhibition) and dehydration, common stressors of the alpine environment, on primary photosynthetic processes in the moss Polytrichum commune from the Czech Republic, the Jeseníky Mountains. Photoinhibition (PI) was studied in fully hydrated thalli of P. commune and during the period of spontaneous desiccation. Time courses of Kautsky kinetics (KK) of ChlF and derived parameters: maximum quantum yield (FV/FM), effective quantum yeld (ΦPSII), and non-photochemical quenching parameters, were measured before and after the samples were treated with high light (1500 µmol m-2 s-1 PAR) for 60 min. Dehydration effects were tested in two sets of experiments with a Pulse-Amplitude-Modulation fluorometry (PAM) and Fast Chlorophyll Fluorescence induction curve (OJIP) techniques. In PAM tests, the desiccating samples were exposed to saturating light pulses every 10 min. in order to obtain ΦPSII and non-photochemical quenching (NPQ). In the second dehydration experiment, OJIP transients of ChlF were repeatedly recorded, OJIP-derived ChlF parameters were plotted against relative water content (RWC) monitored during desiccation. Combined ChF techniques provided insights into the mechanisms activated during P. commune desiccation, such as dissipation of excess absorbed energy through heat dissipation, and conformational changes or destructions of the light harvesting complexes. Combination of stressors resulted in amplified interference with the photosynthetic machinery, even when the added stressor (dehydration) was applied in low dose.

Relationships between chlorophyll fluorescence parameters and photochemical reflectance index of tree species adapted to different temperature regimes

2006 ◽  
Vol 33 (3) ◽  
pp. 241 ◽  
Author(s):  
Jen-Hsien Weng ◽  
Yaw-Nan Chen ◽  
Tien-Szu Liao
Keyword(s):  
Chlorophyll Fluorescence ◽  
Mangifera Indica ◽  
Photochemical Quenching ◽  
Weak Correlation ◽  
Tropical Fruit ◽  
Chlorophyll Fluorescence Parameters ◽  
Psii Efficiency ◽  
Photochemical Reflectance Index ◽  
Fluorescence Parameters ◽  
Leaf Level

Chlorophyll fluorescence parameters and spectral reflectance at leaf level were measured at both predawn and noon, under different temperatures and natural light conditions from autumn to winter. Predawn Fv / Fm of both mango (Mangifera indica L.), a tropical fruit tree, and Podocarpus nagi Zoll. et Moritz., a subtropical conifer, decreased with decreasing temperature, with the former to a greater extent than the latter. Yet, predawn Fv / Fm of Taiwan alder (Alnus formosana Makino), a broadleaf tree widely distributed from the lowlands to 3000 m above sea level in Taiwan, was less influenced by temperature. Nevertheless, taking all three species into consideration, predawn Fv / Fm showed a strong correlation with predawn photochemical reflectance index [(PRIp), PRI = (R531 − R570) / (R531 + R570), where R = reflectance]. For the data obtained at noon, ΔF / Fm′ showed a significant but weak correlation with PRI (PRIn). However, stronger correlation between ΔF / Fm′ and ΔPRI (PRIp − PRIn) was found. In addition, while a non-significant or weak correlation between non-photochemical quenching (NPQ) and PRIn was observed in species sensitive to low temperature, their NPQ was significantly correlated with ΔPRI. We conclude that PRIp can serve as an indicator of the seasonal variation of potential PSII efficiency; and ΔPRI reflects the actual photodissipation as well as actual PSII efficiency during illumination. For the three species in this study, the PRI provides a more consistent measure of the variation in predawn fluorescence values than for steady-state values measured under normal seasonally varying daylight illumination.

scholarly journals Unravelling the physical and physiological basis for the solar-induced chlorophyll fluorescence and photosynthesis relationship

2020 ◽  
Author(s):  
Peiqi Yang ◽  
Christiaan Van der Tol ◽  
Petya K. E. Campbell ◽  
Elizabeth M. Middleton
Keyword(s):  
Chlorophyll Fluorescence ◽  
Heat Dissipation ◽  
Gross Primary Production ◽  
Fluorescence Emission ◽  
Energy Partitioning ◽  
Thermal Dissipation ◽  
Functional Link ◽  
Physiological Basis ◽  
Fluorescence Measurements ◽  
Leaf Level

Abstract. Estimates of the gross terrestrial carbon uptake exhibit large uncertainties. Sun-induced chlorophyll fluorescence (SIF) has an apparent near-linear relationship with gross primary production (GPP). This relationship will potentially facilitate the monitoring of photosynthesis from space. However, the exact mechanistic connection between SIF and GPP is still not clear. To explore the physical and physiological basis for their relationship, we used a unique dataset comprising continuous field measurements of leaf and canopy fluorescence and photosynthesis of corn over a growing season. We found that, at canopy scale, the positive relationship between SIF and GPP was dominated by absorbed photosynthetically active radiation (APAR), which was equally affected by variations in incoming radiation and changes in canopy structure. After statistically controlling these underlying physical effects, the remaining correlation between far-red SIF and GPP due solely to the functional link between fluorescence and photosynthesis at the photochemical level was much weaker. Active leaf-level fluorescence measurements revealed a moderate correlation between the efficiencies of fluorescence emission and photochemistry for sunlit leaves but a weak correlation for shaded leaves. Differentiating sunlit and shaded leaves in the light use efficiency (LUE) models for SIF and GPP facilitates a better understanding of the SIF-GPP relationship at different environmental and canopy conditions. Leaf-level fluorescence measurements also demonstrated that the sustained thermal dissipation efficiency dominated the seasonal energy partitioning while the reversible heat dissipation dominated the diurnal leaf energy partitioning. These diurnal and seasonal variations in heat dissipation underlie, and are thus responsible for, the observed remote sensing-based link between far-red SIF and GPP.  

scholarly journals Remote sensing techniques to assess chlorophyll fluorescence in support of crop monitoring in Poland

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Radosław Gurdak ◽  
Maciej Bartold
Keyword(s):  
Chlorophyll Fluorescence ◽  
Crop Production ◽  
Pearson Correlation ◽  
Vegetation Indices ◽  
Climatic Conditions ◽  
Sugar Beets ◽  
Spectral Vegetation Indices ◽  
Meteorological Observations ◽  
The Impact ◽  
Sentinel 2

AbstractThe increase in demand for food and the need to predict the impact of a warming climate on vegetation makes it critical that the best tools for assessing crop production are found. Chlorophyll fluorescence (ChlF) has been proposed as a direct indicator of photosynthesis and plant condition. The aim of this paper is to study the feasibility of estimating ChlF from spectral vegetation indices derived from Sentinel-2, in order to monitor crop stress and investigate ChlF changes in response to surface temperatures and meteorological observations. The regressions between thirty three Sentinel-2-derived VIs, and ChlF measured on the ground were evaluated in order to estimate the best predictors of ChlF. The r-Pearson correlation and polynomial linear regression were used. For maize, the highest correlation between ChlF and VIs were found for NDII (r=0.65) and for SIPI (r=-0.68). The weakest relationship between VIs and ChlF were found for sugar beets. Despite this, it should be noted that the highest correlation for sugar beets appeared for EVI (r=0.45) and S2REP (r=0.43). The results of this study indicate the need for a synergy of low and high resolution satellite data that will enable a more detailed analysis for estimating fluorescence and its relation to climatic conditions, environmental aspects, and VIs derived from satellite images.

scholarly journals Unraveling the physical and physiological basis for the solar- induced chlorophyll fluorescence and photosynthesis relationship using continuous leaf and canopy measurements of a corn crop

2021 ◽  
Vol 18 (2) ◽  
pp. 441-465
Author(s):  
Peiqi Yang ◽  
Christiaan van der Tol ◽  
Petya K. E. Campbell ◽  
Elizabeth M. Middleton
Keyword(s):  
Chlorophyll Fluorescence ◽  
Heat Dissipation ◽  
Gross Primary Production ◽  
Energy Partitioning ◽  
Thermal Dissipation ◽  
Data Set ◽  
Functional Link ◽  
Physiological Basis ◽  
Fluorescence Measurements ◽  
Leaf Level

Abstract. Estimates of the gross terrestrial carbon uptake exhibit large uncertainties. Sun-induced chlorophyll fluorescence (SIF) has an apparent near-linear relationship with gross primary production (GPP). This relationship will potentially facilitate the monitoring of photosynthesis from space. However, the exact mechanistic connection between SIF and GPP is still not clear. To explore the physical and physiological basis for their relationship, we used a unique data set comprising continuous field measurements of leaf and canopy fluorescence and photosynthesis of corn over a growing season. We found that, at canopy scale, the positive relationship between SIF and GPP was dominated by absorbed photosynthetically active radiation (APAR), which was equally affected by variations in incoming radiation and changes in canopy structure. After statistically controlling these underlying physical effects, the remaining correlation between far-red SIF and GPP due solely to the functional link between fluorescence and photosynthesis at the photochemical level was much weaker (ρ=0.30). Active leaf level fluorescence measurements revealed a moderate positive correlation between the efficiencies of fluorescence emission and photochemistry for sunlit leaves in well-illuminated conditions but a weak negative correlation in the low-light condition, which was negligible for shaded leaves. Differentiating sunlit and shaded leaves in the light use efficiency (LUE) models for SIF and GPP facilitates a better understanding of the SIF–GPP relationship at different environmental and canopy conditions. Leaf level fluorescence measurements also demonstrated that the sustained thermal dissipation efficiency dominated the seasonal energy partitioning, while the reversible heat dissipation dominated the diurnal leaf energy partitioning. These diurnal and seasonal variations in heat dissipation underlie, and are thus responsible for, the observed remote-sensing-based link between far-red SIF and GPP.

scholarly journals Uniform Water Potential Induced by Salt, Alkali, and Drought Stresses Has Different Impacts on the Seedling of Hordeum jubatum: From Growth, Photosynthesis, and Chlorophyll Fluorescence

2021 ◽  
Vol 12 ◽  
Author(s):  
Congcong Shi ◽  
Fan Yang ◽  
Zihao Liu ◽  
Yueming Li ◽  
Xiaolin Di ◽  
...  
Keyword(s):  
Chlorophyll Fluorescence ◽  
Water Potential ◽  
Photochemical Efficiency ◽  
Photosynthetic Performance ◽  
Photochemical Quenching ◽  
Photosynthetic Parameters ◽  
Alkali Stress ◽  
Gas Exchange Parameters ◽  
Hordeum Jubatum ◽  
Damaging Effects

Hordeum jubatum is a halophyte ornamental plant wildly distributed in the Northeast of China, where the low water potential induced by various abiotic stresses is a major factor limiting plant growth and development. However, little is known about the comparative effects of salt, alkali, and drought stresses at uniform water potential on the plants. In the present study, the growth, gas exchange parameters, photosynthetic pigments, and chlorophyll fluorescence in the seedlings of H. jubatum under three low water potentials were measured. The results showed that the growth and photosynthetic parameters under these stresses were all decreased except for carotenoid (Car) with the increasing of stress concentration, and alkali stress caused the most damaging effects on the seedlings. The decreased net photosynthetic rate (Pn), stomatal conductance (Gs), and intercellular CO2 concentrations (Ci) values under salt stress were mainly attributed to stomatal factors, while non-stomatal factors were dominate under drought and alkali stresses. The reduced chlorophyll and slightly increased Car contents occurred under these stresses, and most significant changed under alkali stress. In addition, the maximum photochemical efficiency (Fv/Fm), actual photochemical efficiency (ΦPSII), and photochemical quenching coefficient (qP) under the stresses were all decreased, indicating that salt, alkali, and drought stresses all increased susceptibility of PSII to photoinhibition, reduced the photosynthetic activity by the declined absorption of light for photochemistry, and increased PSII active reaction centers. Moreover, the non-photochemical quenching coefficient (NPQ) of alkali stress was different from salt and drought stresses, showing that the high pH of alkali stress caused more damaging effects on the photoprotection mechanism depending on the xanthophyll cycle. The above results suggest that the H. jubatum has stronger tolerance of salt than drought and alkali stresses, and the negative effects of alkali stress on the growth and photosynthetic performance of this species was most serious.

Seasonal dynamics of spectral vegetation indices at leaf, ecosystem and satellite scales for a boreal evergreen coniferous forest

2020 ◽  
Author(s):  
Chao Zhang ◽  
Jon Atherton ◽  
Paulina Rajewicz ◽  
Anu Riikonen ◽  
Pasi Kolari ◽  
...  
Keyword(s):  
Norway Spruce ◽  
Scots Pine ◽  
Satellite Data ◽  
Seasonal Dynamics ◽  
Recovery Period ◽  
Vegetation Indices ◽  
Near Infrared Reflectance ◽  
Canopy Position ◽  
Spectral Vegetation Indices ◽  
Leaf Level

<div> <p>The spectral vegetation indices (VIs) are widely used in ecology and ecosystem modelling to study carbon uptake and plant responses to climate change. VIs can potentially be used the learn about ecosystem processes at the large scale and used to inform and constrain mechanistic understanding and models. Key VIs such as Normalized Difference Vegetation Index (NDVI) reflects the chlorophyll contents, biomass, and canopy structural changes. The Photochemical Reflectance Index (PRI) and the Chlorophyll Carotenoid Index (CCI) relate to photosynthetic light-use efficiency (LUE) and also capture longer-term pigment changes of the vegetation at leaf and canopy scales, particularly for evergreen species. The Near-Infrared Reflectance of the vegetation (NIRv) relates to the canopy structure. The Water Index (WI) provides leaf water content information. However, the factors that control the seasonal changes of these VIs at different spatial-temporal scales is unclear, hence the question of whether VIs can successfully be scaled from leaf to satellite level remains to be answered. The main objective of this study is to examine, how and why the key VIs (NDVI, PRI, CCI, NIRv and WI etc.) change at the seasonal scale across leaf, ecosystem and satellite data.  </p> </div><div> <p>We use leaf-level measurements, continuous ecosystem observations and satellite data (atmospheric corrected MODIS products-MAIAC) across the spring recovery period of Scots pine (two years data) and Norway spruce (one year data) in a boreal site in Finland to answer: (1) how do VIs change during the photosynthetic spring recovery of the vegetation at leaf, ecosystem and satellite scales? (2) How do environmental and bio-physiological factors affect the seasonal dynamics of VIs? (3) do the main affecting factors change between canopy position and species? (4) whether the main factors change between spatial scales?   </p> </div><div> <p>Our preliminary results show that at the leaf level of Scots pine, both PRI and CCI are more strongly correlated with LUE at top-canopy (r = 0.92 and 0.93, respectively) than at low-canopy (r = 0.63 and 0.72) positions. At the leaf level in Norway spruce, only top-canopy PRI and CCI are significantly correlated with LUE (r > 0.75). When focusing on the correlations with PRI and CCI with pigments, we found that in Scots pine needles and for both top and low canopy, more than 80% of variation in PRI and CCI are explained by Car/Chl ratio and de-epoxidation state of xanthophyll cycle pigments (DEPS), respectively. However, in spruce for both canopy positions, the strongest correlation with PRI and CCI is lutein/Chl ratio (r is between -0.97 and -0.85), respectively), followed by Car/Chl ratio (r is between -0.84 and -0.72). At the ecosystem level, the PRI is correlated with GPP (gross primary productivity) when winter data and low PAR (<350 μmol m<sup>−2</sup> s<sup>−1</sup>) is not considered (r = 0.63). The other VIs are under investigation and will also be presented. As a tentative conclusion, although optical properties covary with photosynthesis, mechanisms of variation appear species and light environment specific.  </p> </div>

scholarly journals Can Vegetation Indices Serve as Proxies for Potential Sun-Induced Fluorescence (SIF)? A Fuzzy Simulation Approach on Airborne Imaging Spectroscopy Data

2021 ◽  
Vol 13 (13) ◽  
pp. 2545
Author(s):  
Subhajit Bandopadhyay ◽  
Anshu Rastogi ◽  
Sergio Cogliati ◽  
Uwe Rascher ◽  
Maciej Gąbka ◽  
...  
Keyword(s):  
Fuzzy Logic ◽  
Plant Cover ◽  
Vegetation Indices ◽  
Imaging Spectroscopy ◽  
Controlling Factors ◽  
Photochemical Quenching ◽  
Spectral Vegetation Indices ◽  
Airborne Imaging ◽  
Non Photochemical Quenching ◽  
Modelling Approach

In this study, we are testing a proxy for red and far-red Sun-induced fluorescence (SIF) using an integrated fuzzy logic modelling approach, termed as SIFfuzzy and SIFfuzzy-APAR. The SIF emitted from the core of the photosynthesis and observed at the top-of-canopy is regulated by three major controlling factors: (1) light interception and absorption by canopy plant cover; (2) escape fraction of SIF photons (fesc); (3) light use efficiency and non-photochemical quenching (NPQ) processes. In our study, we proposed and validated a fuzzy logic modelling approach that uses different combinations of spectral vegetation indices (SVIs) reflecting such controlling factors to approximate the potential SIF signals at 760 nm and 687 nm. The HyPlant derived and field validated SVIs (i.e., SR, NDVI, EVI, NDVIre, PRI) have been processed through the membership transformation in the first stage, and in the next stage the membership transformed maps have been processed through the Fuzzy Gamma simulation to calculate the SIFfuzzy. To test whether the inclusion of absorbed photosynthetic active radiation (APAR) increases the accuracy of the model, the SIFfuzzy was multiplied by APAR (SIFfuzzy-APAR). The agreement between the modelled SIFfuzzy and actual SIF airborne retrievals expressed by R2 ranged from 0.38 to 0.69 for SIF760 and from 0.85 to 0.92 for SIF687. The inclusion of APAR improved the R2 value between SIFfuzzy-APAR and actual SIF. This study showed, for the first time, that a diverse set of SVIs considered as proxies of different vegetation traits, such as biochemical, structural, and functional, can be successfully combined to work as a first-order proxy of SIF. The previous studies mainly included the far-red SIF whereas, in this study, we have also focused on red SIF along with far-red SIF. The analysis carried out at 1 m spatial resolution permits to better infer SIF behaviour at an ecosystem-relevant scale.

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