Plant canopy interception of photosynthetically active radiation (PAR) drives carbon dioxide (CO2), water and energy cycling in the soil-plant-atmosphere system. Quantifying intercepted PAR requires accurate measurements of total incident PAR above canopies and direct beam and diffuse PAR components. While some regional data sets include these data, e.g. from Atmospheric Radiation Measurement (...

The efficiency with which incoming photosynthetically active radiation (PAR) is intercepted by a canopy depends on the proportions of diffuse and direct radiation in the incoming PAR. In the present work, we developed a comparison between two spectral cloudless sky parameterization schemes in terms of their capability to provide accurate estimates of global, diffuse and direct incoming PAR. Bot...

Light-emitting diodes (LED), which are designed as quasi-monochromatic light sources, can also function as spectrally selective photodiodes. This provides a new kind of photosynthetically active radiation (PAR) sensor that is inexpensive and has much better stability over time than interference filters used in some PAR sensors. The action spectrum of photosynthesis in green plants has principle...

Accurate light measurements are important in the analysis of photosynthetic systems. Many commercial instruments are available to determine light; however, the comparison of light estimates between studies is difficult due to the differences in sensor types and their calibrations. The measurement of underwater irradiance is also complicated by the scattering and attenuation of light due to inte...

Plants are continuously subjected to UV-B radiation (UV-B; 280-320 nm) as a component of sunlight causing damage to the genome. For elimination of DNA damage, a set of repair mechanisms, mainly photoreactivation, excision, and recombination repair, has evolved. Whereas photoreactivation and excision repair have been intensely studied during the last few years, recombination repair, its regulati...

Photosynthetic photon flux density (PPFD) regimes within vegetation canopies are intrinsically heterogeneous in time and space. Photosynthesis responds to changes in the intensity and temporal variability of PPFD in a non-linear way. Therefore, it is important to quantify PPFD heterogeneity at short time scales in order to better understand and assess plant–atmosphere carbon exchange from the s...

Relationship between fraction of radiation absorbed by photosynthesizing maize and soybean canopies and NDVI from remotely sensed data taken at close range and from MODIS 250 m resolution data" a b s t r a c t a r t i c l e i n f o The fraction of incident photosynthetically active radiation absorbed by the photosynthesizing tissue in a canopy (fAPAR) is a key variable in the assessment of vege...

[1] Dimethylsulphide (DMS) is a climatically important component of global biogeochemical cycles, through its role in the sulphur cycle. Changes in ultraviolet radiation (UV) exhibit both positive and negative forcings on the dynamics of production and turnover of DMS and its precursor dimethylsulphoniopropionate (DMSP). In this study we investigate the net forcing of UV on atmospheric DMS. The...

UVB alters photosynthetic rate, fatty acid profiles and morphological characteristics of phytoplankton. Copepods, important grazers of primary production, select algal cells based upon their size, morphological traits, nutritional status, and motility. We investigated the grazing rates of the copepod Calanus finmarchicus on the diatom Thalassiosira weissflogii cultured under 3 levels of ultravi...