•SIF760 tracks the diurnal variations in GPP over C3/C4 crop canopies well.•SIF760 is linearly correlated with GPP for C3 and C4 crops at the diurnal scale.•The slope of the GPP–SIF760 relationship ...is higher for C4 crops.•The large difference in εP between C3 and C4 crops determines the difference in the slope εPεF.•The photosynthetic type should be considered when discussing the GPP–SIF relationship.
Accurate estimation of gross primary production (GPP) is of great importance to global change research and also food and fuel security. Previous studies have demonstrated that values of sun-induced chlorophyll fluorescence (SIF) retrieved from hyperspectral data provide a direct measure of ecosystem GPP. However, global analysis of the relationship between satellite SIF and model-based GPP indicates that the relationship between the two parameters is highly dependent on the plant functional type (PFT). The overarching goal of this study is to examine the potential of far-red SIF retrieved at 760nm (SIF760) to track the diurnal variations in GPP for C3 and C4 crops, and to investigate whether the GPP–SIF relationship is dependent on the type of photosynthesis. GPP values are estimated from flux tower records and daily SIF760 data are derived from ground-based spectral measurements. The results show that GPP and SIF760 have similar diurnal patterns and are linearly correlated for C3 and C4 crops. However, the ratio of εP to εF (the slope of the linear SIF-based GPP model, GPP=εPεF×SIF) for C3 wheat is about 46% of that for C4 maize. The findings from the diurnal variation experiments imply that theεF is weakly sensitive to the photosynthetic pathway type (PsP type) and that the large difference in εP between C3 and C4 crops leads to the difference in the slopes. Our studies confirm the capability of the remotely sensed SIF signals to act as a direct proxy for GPP and suggest that the PsP type should be considered when trying to accurately quantify the ecosystem productivity using the straightforward empirical approach.
The Fraunhofer line discrimination (FLD) principle is the main approach used for the retrieval of solar-induced chlorophyll fluorescence (SIF). The basic assumption of the FLD principle is that the ...apparent reflectance spectra without SIF in-filling are smooth in the region of the absorption bands. However, in fact, this assumption is not valid due to the so-called 'direct radiation in-filling' effect caused by the nonlinear contribution of direct and diffuse radiation at the oxygen absorption bands, which are widely used for ground-based SIF retrieval. In this study, we first analysed the physical mechanism of the direct radiation in-filling effect on the oxygen absorption bands and found that the bias in the SIF retrieval caused by the direct radiation in-filling effect at the oxygen-A (O
2
-A) band was less than 20% based on the use of a simulated data set. Second, we established a simple correction model of the direct radiation in-filling effect. We found that the direct radiation in-filling effect at the O
2
-A band was directly proportional to the difference between the reflectance of the direct and diffuse radiation, and that the coefficient of proportionality was well correlated with the diffuse-to-global radiation ratio in the form of a quadratic function, with a coefficient of determination (R
2
) of 0.97. Finally, the model was validated using both simulated and field data sets. The validation results show that the bias in the SIF retrieval caused by the direct radiation in-filling effect can be efficiently corrected using the model proposed in this article. This study thus provides a possible approach to estimating and correcting for the direct radiation-infilling effect using prior knowledge of the bidirectional reflectance distribution function characteristics of direct and diffuse radiation for specific targets.
Numerous observations and modeling results have shown that there is noticeable directional variation in the solar-induced chlorophyll fluorescence (SIF), and this has not been well investigated. In ...this paper, 16 multiangular spectral observations were carried out on winter wheat to assess the bidirectional SIF emission. First, the bidirectional SIF emission was retrieved from the spectral measurements made by a high-performance QE Pro spectrometer and an automatic multiangle observation system using the 3FLD algorithm. The bidirectional shape of the SIF emission was found to be similar to that of the canopy reflectance in the solar principal plane, with a mean correlation coefficient of 0.94 and 0.97 at the O 2 -B and O 2 -A bands, respectively. The modified Rahman-Pinty-Verstraete (MRPV) model, a semiempirical bidirectional reflectance distribution function (BRDF) model, was then employed to describe the bidirectional variation in the SIF and reflectance with a mean root-mean-square-error value of 0.036 and 0.041 mW m -2 sr -1 nm -1 for the SIF at the O 2 -B and O 2 -A bands, respectively. Finally, both the bidirectional reflectance and SIF were BRDF corrected to nadir using the MRPV model. Most of the directional variation was successfully corrected by this method-the mean correction ratios were 87% and 81% for the reflectance at the O 2 -B and O 2 -A bands and 84% and 72% for the SIF at the O 2 -B and O 2 -A bands, respectively. Therefore, the SIF emission cannot be regarded as isotropic, and the high similarity between the bidirectional SIF and reflectance, together with the BRDF correction results, indicates that the bidirectional SIF emission can be adjusted using either the BRDF reflectance models or prior knowledge.
Solar-induced chlorophyll fluorescence (SIF), an electromagnetic signal that can potentially indicate vegetation photosynthetic activity, can be retrieved from ground-based, airborne and satellite ...measurements. However, due to the scattering and re-absorption effects inside the leaves and canopy, SIF measured at the canopy level is only a small part of the total SIF emission at the photosystem level. Therefore, a downscaling mechanism of SIF from the canopy level to the photosystem level is important for better understanding the relationship between SIF and the vegetation gross primary production (GPP). In this study, firstly, we analyzed the canopy scattering effects using a simple parameterization model based on the spectral invariant theory. The probability for SIF photons to escape from the canopy was found to be related to the anisotropic spectral reflectance, canopy interception of the upward solar radiation, and leaf absorption. An empirical approach based on a Random Forest (RF) regression algorithm was applied to downscale SIF constrained by the red, red-edge and far-red anisotropic reflectance. The RF was trained using simulations conducted with the Soil Canopy Observation, Photochemistry and Energy fluxes (SCOPE) model. The performance of the SIF downscaling method was evaluated with SCOPE and Discrete Anisotropic Radiative Transfer (DART) model simulations, ground measurements and airborne data. Results show that estimated SIF at the photosystem level matches well with simulated reference data, and the relationship between SIF and photosynthetically active radiation absorbed by chlorophyll is improved by SIF downscaling. This finding in combination with other evaluation criteria suggests the downscaling of canopy SIF as an efficient strategy to normalize species dependent effects of canopy structure and varying solar-view geometries. Based on our results for the SIF-APAR relationship, we expect that such normalization approaches can be helpful to improve estimates of photosynthesis using remote sensing measurements of SIF.
•A practical method for SIF downscaling from canopy level to photosystem level.•Random forest is efficient for the estimation of SIF escape probability.•Only reflectance at red, red-edge and far-red bands are needed for SIF downscaling.•The method is effective for ground-based and airborne SIF measurements.•The relationship between SIF and APAR can be improved by SIF downscaling.
Solar-induced chlorophyll fluorescence (SIF), which can be used as a novel proxy for estimating gross primary production (GPP), can be effectively retrieved using ground-based, airborne and satellite ...measurements. Absorbed photosynthetically active radiation (APAR) is the key bridge linking SIF and GPP. Remotely sensed SIF at the canopy level ( SIFcanopy ) is only a part of the total SIF emission at the photosystem level. An SIF-based model for GPP estimation would be strongly influenced by the fraction of SIF photons escaping from the canopy ( fesc ). Understanding the response of SIFcanopy to the absorbed photosynthetically active radiation absorbed by chlorophyll ( APARchl ) is a key step in estimating GPP but, as yet, this has not been well explored. In this study, we aim to investigate the relationship between remotely sensed SIFcanopy and APARchl based on simulations made by the Soil Canopy Observation Photosynthesis Energy fluxes (SCOPE) model and field measurements. First, the ratio of the fraction of the absorbed photosynthetically active radiation absorbed by chlorophyll ( fPARchl ) to the fraction of absorbed photosynthetically active radiation absorbed by green leaves ( fPARgreen ) is investigated using a dataset simulated by the SCOPE model. The results give a mean value of 0.722 for Cab at 5 μg cm−2, 0.761 for Cab at 10 μg cm−2 and 0.795 for other Cab content (ranging from 0.71 to 0.81). The response of SIFcanopy to APARchl is then explored using simulations corresponding to different biochemical and biophysical conditions and it is found that SIFcanopy is well correlated with APARchl . At the O2-A band, for a given plant type, the relationship between SIFcanopy and APARchl can be approximately expressed by a linear statistical model even for different values of the leaf area index (LAI) and chlorophyll content, whereas the relationship varies with the LAI and chlorophyll content at the O2-B band. Finally, the response of SIFcanopy to APARchl for different leaf angle distribution (LAD) functions is investigated using field observations and simulations; the results show that fesc is larger for a planophile canopy structure. The values of the ratio of SIFcanopy to APARchl are 0.0092 ± 0.0020 , 0.0076 ± 0.0036 and 0.0052 ± 0.0004 μm−1 sr−1 for planophile vegetables/crops, planophile grass and spherical winter wheat, respectively, at the O2-A band. At the O2-B band, the ratios are 0.0063 ± 0.0014 , 0.0049 ± 0.0030 and 0.0033 ± 0.0004 μm−1 sr−1, respectively. The values of this ratio derived from observations agree with simulations, giving values of 0.0055 ± 0.0002 and 0.0068 ± 0.0001 μm−1 sr−1 at the O2-A band and 0.0032 ± 0.0002 and 0.0047 ± 0.0001 μm−1 sr−1 at the O2-B band for spherical and planophile canopies, respectively. Therefore, both the simulations and observations confirm that the relationship between SIFcanopy and APARchl is species-specific and affected by biochemical components and canopy structure, especially at the O2-B band. It is also very important to correct for reabsorption and scattering of the SIF radiative transfer from the photosystem to the canopy level before the remotely sensed SIFcanopy is linked to the GPP.
Objective
This study aimed to summarize the clinical phenotype and genotype of children with epilepsy caused by GABRA1 gene variants.
Methods
Eight epilepsy patients, who were admitted to Qilu ...Hospital of Shandong University from 2015 to 2021, were enrolled in the study. GABRA1 gene variants were detected by whole-exome sequencing. Epilepsy clinical manifestations, electroencephalography, neuroimaging characteristics and treatment methods were retrospectively analyzed.
Results
Among the eight patients, four were males and four were females. Epilepsy onset age was between 3 and 8 months of age. Two patients had a family history of epilepsy. Six cases were
de
novo variants, and two were hereditary variants. Two children carried the same pathogenic variants, and five carried novel pathogenic variants that had not been reported internationally. The types of seizures were diverse, including focal seizures in five cases, generalized tonic-clonic seizures in five cases, and spasms in two cases. Electroencephalography of seven cases showed abnormal background rhythms, and six cases showed abnormal discharge during the interictal period. No obvious abnormalities were found on magnetic resonance imaging in five cases. All eight children had different degrees of developmental retardation.
Conclusion
De novo
pathogenic variants in GABRA1 are more common than inherited pathogenic variants, and most epilepsy symptoms begin in the first year of life, manifesting with a variety of seizure types and developmental delays. Conventional treatment usually involves one or more drugs; although drug treatment can control seizures in some cases, cognitive and developmental deficits often exist. The five newly discovered pathogenic variants enrich the GABRA1 gene pathogenic variant spectrum.
Solar-induced chlorophyll fluorescence (SIF) is regarded as a proxy for photosynthesis in terrestrial vegetation. Tower-based long-term observations of SIF are very important for gaining further ...insight into the ecosystem-specific seasonal dynamics of photosynthetic activity, including gross primary production (GPP). Here, we present the design and operation of the tower-based automated SIF measurement (SIFSpec) system. This system was developed with the aim of obtaining synchronous SIF observations and flux measurements across different terrestrial ecosystems, as well as to validate the increasing number of satellite SIF products using in situ measurements. Details of the system components, instrument installation, calibration, data collection, and processing are introduced. Atmospheric correction is also included in the data processing chain, which is important, but usually ignored for tower-based SIF measurements. Continuous measurements made across two growing cycles over maize at a Daman (DM) flux site (in Gansu province, China) demonstrate the reliable performance of SIF as an indicator for tracking the diurnal variations in photosynthetically active radiation (PAR) and seasonal variations in GPP. For the O
-A band in particular, a high correlation coefficient value of 0.81 is found between the SIF and seasonal variations of GPP. It is thus concluded that, in coordination with continuous eddy covariance (EC) flux measurements, automated and continuous SIF observations can provide a reliable approach for understanding the photosynthetic activity of the terrestrial ecosystem, and are also able to bridge the link between ground-based optical measurements and airborne or satellite remote sensing data.
The accurate estimation of anthropogenic carbon emissions is of great significance for understanding the global carbon cycle and guides the setting and implementation of global climate policy and CO2 ...emission-reduction goals. This study built a data-driven stacked random forest regression model for estimating gridded global fossil fuel CO2 emissions. The driving variables include the annual features of column-averaged CO2 dry-air mole fraction (XCO2) anomalies based on their ecofloristic zone, night-time light data from the Visible Infrared Imaging Radiometer Suite (VIIRS), terrestrial carbon fluxes, and vegetation parameters. A two-layer stacked random forest regression model was built to fit 1° gridded inventory of open-source data inventory for anthropogenic CO2 (ODIAC). Then, the model was trained using the 2014–2018 dataset to estimate emissions in 2019, which provided a higher accuracy compared with a single-layer model with an R2 of 0.766 and an RMSE of 0.359. The predicted gridded emissions are consistent with Global Carbon Grid at 1° scale with an R2 of 0.665, and the national total emissions provided a higher R2 at 0.977 with the Global Carbon Project (GCP) data, as compared to the ODIAC (R2 = 0.956) data, in European countries. This study demonstrates that data-driven random forest regression models are capable of estimating anthropogenic CO2 emissions at a grid scale.
Recent studies have demonstrated that solar-induced chlorophyll fluorescence (SIF) can offer a new way for directly estimating the terrestrial gross primary production (GPP). The main objective of ...this study is to investigate whether the red or far-red SIF is a better indicator of GPP using both simulations by the SCOPE model (Soil Canopy Observation, Photochemistry and Energy fluxes) and the observations of winter wheat at the canopy level. The results showed that: (1) both far-red SIF and GPP increased with leaf area index (LAI), whereas the red SIF quickly reached its saturation with an LAI value of 2 due to the strong reabsorption effect; (2) the diurnal GPP could be robustly estimated from the SIF spectra for winter wheat at each growth stage, whereas the correlation weakened greatly at the red band if all the observations made at different growth stages or all the simulations with different LAI values were pooled together - a situation that did not occur at the far-red band; (3) the SIF-based GPP models derived from the 2016 observations were well validated using the data set from 2015, with a root mean square error (RMSE) value of 0.128 and 0.133 (mg m
−2
s
−1
) at the oxygen-A (O
2
-A) band and oxygen-B (O
2
-B) band, respectively. Therefore, the far-red SIF may be more reliable for mapping GPP for remote-sensing applications with heterogeneous and diverse vegetation growth conditions.
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