•Continuous timeseries of spectral irradiance are needed to study plant photobiology.•Atmospheric water-vapour & ozone column thickness affect daily spectral irradiance.•Photon ratios affecting plant ...photobiology varied on a daily and seasonal basis.•Proxy model development for photon ratios would facilitate result interpretation.
Plants rely on spectral cues present in their surroundings, generated by the constantly changing light environment, to guide their growth and reproduction. Photoreceptors mediate the capture of information by plants from the light environment over a wide range of wavelengths, but despite extensive evidence that plants respond to various light cues, only fragmentary data have been published showing patterns of diurnal, seasonal and geographical variation in the spectral composition of daylight. To illustrate patterns in spectral photon ratios, we measured time series of irradiance spectra at two distinct geographical and climatological locations, Helsinki, Finland and Gual Pahari, India. We investigated the drivers behind variation of the spectral photon ratios measured at these two locations, based on the analysis of over 400 000 recorded spectra. Differences in spectral irradiance were explained by different atmospheric factors identified through multiple regression model analysis and comparison to spectral irradiance at ground level simulated with a radiative transfer model. Local seasonal and diurnal changes in spectral photon ratios were related to solar elevation angle, atmospheric water-vapour content and total ozone column thickness and deviated from their long-term averages to an extent likely to affect plant photobiology. We suggest that future studies should investigate possible effects of varying photon ratios on terrestrial plants. Solar elevation angle especially affects the patterns of B:G and B:R ratios. Water vapour has a large effect on the R:FR photon ratio and modelled climate scenarios predict that increasing global temperatures will result in increased atmospheric water vapour. The development of proxy models, utilising available data from weather and climate models, for relevant photon ratios as a function of solar elevation angle and atmospheric factors would facilitate the interpretation of results from past, present and future field studies of plants and vegetation.
This work presents a validation of three satellite-based radiation products over an extensive network of 313 pyranometers across Europe, from 2005 to 2015. The products used have been developed by ...the Satellite Application Facility on Climate Monitoring (CM SAF) and are one geostationary climate dataset (SARAH-JRC), one polar-orbiting climate dataset (CLARA-A2) and one geostationary operational product. Further, the ERA-Interim reanalysis is also included in the comparison. The main objective is to determine the quality level of the daily means of CM SAF datasets, identifying their limitations, as well as analyzing the different factors that can interfere in the adequate validation of the products.
The quality of the pyranometer was the most critical source of uncertainty identified. In this respect, the use of records from Second Class pyranometers and silicon-based photodiodes increased the absolute error and the bias, as well as the dispersion of both metrics, preventing an adequate validation of the daily means. The best spatial estimates for the three datasets were obtained in Central Europe with a Mean Absolute Deviation (MAD) within 8–13W/m2, whereas the MAD always increased at high-latitudes, snow-covered surfaces, high mountain ranges and coastal areas. Overall, the SARAH-JRC's accuracy was demonstrated over a dense network of stations making it the most consistent dataset for climate monitoring applications. The operational dataset was comparable to SARAH-JRC in Central Europe, but lacked of the temporal stability of climate datasets, while CLARA-A2 did not achieve the same level of accuracy despite predictions obtained showed high uniformity with a small negative bias. The ERA-Interim reanalysis shows the by-far largest deviations from the surface reference measurements.
•Validation of daily means of CM-SAF satellite products over 313 ground stations•SARAH provides the best estimations of solar radiation over Europe.•Low quality pyranometers are a significant uncertainty source in the validation.
Cryptochromes (CRYs) and UV RESISTANCE LOCUS 8 (UVR8) photoreceptors perceive UV-A/blue (315-500 nm) and UV-B (280-315 nm) radiation in plants, respectively. While the roles of CRYs and UVR8 have ...been studied in separate controlled-environment experiments, little is known about the interaction between these photoreceptors. Here, Arabidopsis wild-type Ler, CRYs and UVR8 photoreceptor mutants (uvr8-2, cry1cry2 and cry1cry2uvr8-2), and a flavonoid biosynthesis-defective mutant (tt4) were grown in a sun simulator. Plants were exposed to filtered radiation for 17 d or for 6 h, to study the effects of blue, UV-A, and UV-B radiation. Both CRYs and UVR8 independently enabled growth and survival of plants under solar levels of UV, while their joint absence was lethal under UV-B. CRYs mediated gene expression under blue light. UVR8 mediated gene expression under UV-B radiation, and in the absence of CRYs, also under UV-A. This negative regulation of UVR8-mediated gene expression by CRYs was also observed for UV-B. The accumulation of flavonoids was also consistent with this interaction between CRYs and UVR8. In conclusion, we provide evidence for an antagonistic interaction between CRYs and UVR8 and a role of UVR8 in UV-A perception.
Ground level UV-B (290–315 nm) and UV-A (315–400 nm) radiation regulates multiple aspects of plant growth and development. In a natural environment, UV radiation interacts in a complex manner with ...other environmental factors (e.g., drought) to regulate plants’ morphology, physiology, and growth. To assess the interactive effects of UV radiation and soil drying on plants’ secondary metabolites and transcript abundance, we performed a field experiment using two different accessions of
Medicago truncatula
(F83005-5 French origin and Jemalong A17 Australian origin). Plants were grown for 37 days under long-pass filters to assess the effects of UV short wavelength (290–350 nm, UV
sw
) and UV-A long wavelength (350–400 nm, UV-A
lw
). Soil–water deficit was induced by not watering half of the plants during the last seven days of the experiment. The two accessions differed in the concentration of flavonoids in the leaf epidermis and in the whole leaf: F83005-5 had higher concentration than Jemalong A17. They also differed in the composition of the flavonoids: a greater number of apigenin derivatives than tricin derivatives in Jemalong A17 and the opposite in F83005-5. Furthermore, UV
sw
and soil drying interacted positively to regulate the biosynthesis of flavonoids in Jemalong A17 through an increase in transcript abundance of
CHALCONE SYNTHASE (CHS).
However, in F83005-5, this enhanced
CHS
transcript abundance was not detected. Taken together the observed metabolite and gene transcript responses suggest differences in mechanisms for acclimation and stress tolerance between the accessions.
Graphical abstract
Photomorphogenic responses triggered by low fluence rates of ultraviolet B radiation (UV-B; 280-315 nm) are mediated by the UV-B photoreceptor UV RESISTANCE LOCUS8 (UVR8). Beyond our understanding of ...the molecular mechanisms of UV-B perception by UVR8, there is still limited information on how the UVR8 pathway functions under natural sunlight. Here, wildtype Arabidopsis (Arabidopsis thaliana) and the uvr8-2 mutant were used in an experiment outdoors where UV-A (315-400 and UV-B irradiances were attenuated using plastic films. Gene expression, PYRIDOXINE BIOSYNTHESIS1 (PDX1) accumulation, and leaf metabolite signatures were analyzed. The results show that UVR8 is required for transcript accumulation of genes involved in UV protection, oxidative stress, hormone signal transduction, and defense against herbivores under solar UV. Under natural UV-A irradiance, UVR8 is likely to interact with UV-A/blue light signaling pathways to moderate UV-B-driven transcript and PDX1 accumulation. UVR8 both positively and negatively affects UV-Aregulated gene expression and metabolite accumulation but is required for the UV-B induction of phenolics. Moreover, UVR8-dependent UV-B acclimation during the early stages of plant development may enhance normal growth under long-term exposure to solar UV.
•Global changes in cloudiness and pollution affects the sunlight received by plants.•The effect of diffuse solar radiation on canopy photosynthesis is multilayered.•We discuss these processes at the ...atmospheric, canopy and leaf level.•Canopy structural traits impact how diffuse fraction affect microclimatic changes.•Photobiology is affected by changes in the spectral composition of radiation.
The sunlight received by plants is affected by cloudiness and pollution. Future changes in cloud cover will differ among regions, while aerosol concentrations are expected to continue increasing globally as a result of wildfires, fossil fuel combustion, and industrial pollution. Clouds and aerosols increase the diffuse fraction and modify the spectral composition of incident solar radiation, and both will affect photosynthesis and terrestrial ecosystem productivity. Thus, an assessment of how canopy and leaf-level processes respond to these changes is needed as part of accurately forecasting future global carbon assimilation. To review these processes and their implications: first, we discuss the physical basis of the effect of clouds and aerosols on solar radiation as it penetrates the atmosphere; second, we consider how direct and diffuse radiation are absorbed and transmitted by plant canopies and their leaves; and finally, we assess the consequences for photosynthesis at the canopy and ecosystem levels. Photobiology will be affected at the atmospheric level by a shift in spectral composition toward shorter or longer wavelengths under clouds or aerosols, respectively, due to different scattering. Changes in the microclimate and spectral composition of radiation due to an enhanced diffuse fraction also depend on the acclimation of canopy architectural and physiological traits, such as leaf area index, orientation, and clumping. Together with an enhancement of light-use efficiency, this makes the effect of diffuse solar radiation on canopy photosynthesis a multilayered phenomenon, requiring experimental testing to capture those complex interactions that will determine whether it produces the persistent enhancement in carbon assimilation that land-surface models currently predict.
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Plants synthesize phenolic compounds in response to certain environmental signals or stresses. One large group of phenolics, flavonoids, is considered particularly responsive to ultraviolet (UV) ...radiation. However, here we demonstrate that solar blue light stimulates flavonoid biosynthesis in the absence of UV‐A and UV‐B radiation. We grew pea plants (Pisum sativum cv. Meteor) outdoors, in Finland during the summer, under five types of filters differing in their spectral transmittance. These filters were used to (1) attenuate UV‐B; (2) attenuate UV‐B and UV‐A < 370 nm; (3) attenuate UV‐B and UV‐A; (4) attenuate UV‐B, UV‐A and blue light; and (5) as a control not attenuating these wavebands. Attenuation of blue light significantly reduced the flavonoid content in leaf adaxial epidermis and reduced the whole‐leaf concentrations of quercetin derivatives relative to kaempferol derivatives. In contrast, UV‐B responses were not significant. These results show that pea plants regulate epidermal UV‐A absorbance and accumulation of individual flavonoids by perceiving complex radiation signals that extend into the visible region of the solar spectrum. Furthermore, solar blue light instead of solar UV‐B radiation can be the main regulator of phenolic compound accumulation in plants that germinate and develop outdoors.
This paper presents validation results of the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System MACC (Monitoring Atmospheric Composition and Climate) ...re-analysis aerosol optical depth (AOD) for the period 2003-2006. We evaluate the MACC AOD at a UV wavelength (340 nm) and at mid-visible (500 and 550 nm) by comparing against ground-based AERONET measurements at 12 sites. The AERONET sites cover various parts of the globe and are categorized in three groups: urban/anthropogenic, biomass burning and dust, depending on the typically dominating aerosol type. This is the first time a global model such as the ECMWF has been evaluated for the performance of AOD at a UV wavelength. The results show that the MACC system generally provides a good representation of the AOD on a monthly basis, showing a realistic seasonal cycle. The model is mostly able to capture major dust load events and also the peak months of biomass burning correctly. For Kanpur and Solar Village, however, the model overestimates the AOD during the monsoon period when the aerosol load is generally low. When comparing hourly AOD values, the model-measurement agreement is better for biomass burning and dust sites than for urban sites, with an average correlation coefficient around 0.90 for biomass burning sites, around 0.77 for dust sites, and below 0.70 for urban sites. The AOD at 500 nm averaged over all sites shows only a small systematic difference between modeled and measured values, with a relative mean bias of 0.02. However, for the AOD at 340 nm the relative mean bias is -0.2. All sites included in the study show a relative mean bias at 340 nm smaller (or more negative) than that at 500 nm, indicating a strong wavelength dependence in the performance of the AOD in the MACC system. A comparison against fine and coarse mode AOD of the AERONET indicates that this has to do with the size distribution of the model: generally, the ECMWF model overestimates the contribution by coarse mode particles.
The TROPOMI surface UV algorithm Lindfors, Anders V; Kujanpää, Jukka; Kalakoski, Niilo ...
Atmospheric measurement techniques,
02/2018, Letnik:
11, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The TROPOspheric Monitoring Instrument (TROPOMI) is the only payload of the
Sentinel-5 Precursor (S5P), which is a polar-orbiting satellite mission of
the European Space Agency (ESA). TROPOMI is ...a nadir-viewing spectrometer
measuring in the ultraviolet, visible, near-infrared, and the shortwave
infrared that provides near-global daily coverage. Among other things,
TROPOMI measurements will be used for calculating the UV radiation reaching
the Earth's surface. Thus, the TROPOMI surface UV product will contribute to
the monitoring of UV radiation by providing daily information on the
prevailing UV conditions over the globe. The TROPOMI UV algorithm builds on
the heritage of the Ozone Monitoring Instrument (OMI) and the Satellite
Application Facility for Atmospheric Composition and UV Radiation (AC SAF)
algorithms. This paper provides a description of the algorithm that will be
used for estimating surface UV radiation from TROPOMI observations. The
TROPOMI surface UV product includes the following UV quantities: the UV
irradiance at 305, 310, 324, and 380 nm; the erythemally weighted UV;
and the vitamin-D weighted UV. Each of these are available as (i) daily dose or
daily accumulated irradiance, (ii) overpass dose rate or irradiance, and
(iii) local noon dose rate or irradiance. In addition, all quantities are
available corresponding to actual cloud conditions and as clear-sky values,
which otherwise correspond to the same conditions but assume a cloud-free
atmosphere. This yields 36 UV parameters altogether. The TROPOMI UV algorithm
has been tested using input based on OMI and the Global Ozone Monitoring
Experiment-2 (GOME-2) satellite measurements. These preliminary results
indicate that the algorithm is functioning according to expectations.
The climatological surface solar radiation (SSR; also called global radiation), which is largely dependent on cloud conditions, is an important indicator of the solar energy production potential. In ...the Baltic area, previous studies have indicated lower cloud amounts over seas than over land, in particular during the summer. However, the existing literature on the SSR climate or how it translates into solar energy potential has not paid much attention to how the SSR behaves quantitatively in relation to the coastline. In this paper, we have studied the climatological land–sea contrast of the SSR over the Baltic area. For this, we used two satellite climate data records, CLARA-A2 and SARAH-2, together with a coastline data base and ground-based pyranometer measurements of the SSR. We analyzed the behaviour of the climatological mean SSR over the period 2003–2013 as a function of the distance to the coastline. The results show that off-shore locations on average receive higher SSR than inland areas and that the land–sea contrast in the SSR is strongest during the summer. Furthermore, the land–sea contrast in the summer time SSR exhibits similar behavior in various parts of the Baltic. For CLARA-A2, which shows better agreement with the ground-based measurements than SARAH-2, the annual SSR is 8% higher 20 km off the coastline than 20 km inland. For summer, i.e., June–August, this difference is 10%. The observed land–sea contrast in the SSR is further shown to correspond closely to the behavior of clouds. Here, convective clouds play an important role as they tend to form over inland areas rather than over the seas during the summer part of the year.
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