Quantifying UV radiation

In this handbook we discuss methods relevant to research on the responses of plants to ultraviolet (UV) radiation. We also summarize the knowledge needed to make informed decisions about manipulation and quantification of UV radiation, and the design of UV experiments. We give guidelines and practical recommendations for obtaining reliable and relevant data and interpretations. We cover research both on terrestrial and aquatic plants (seaweeds, marine angiosperms and freshwater higher plants are included, but microalgae are excluded from the scope of this work). We consider experimentation on ecological, eco-physiological and physiological questions. The handbook will be most useful to early stage researchers (ESRs). However, more experienced researchers will also find information of interest. The guidelines themselves, we hope, will ensure a high and uniform standard of quality for UV research within our COST action, and the whole UV research community. We have written this text so that it is useful both for reading from cover to cover and for reference. It will also be useful as a textbook for training workshops aimed at ESRs. Physiological and eco-physiological experiments can attempt to respond to different objective questions: (1) will a future increase in UV radiation affect growth and morphology of plants? (2) what is the effect of current UV radiation levels on plant growth and morphology? (3) what are the mechanisms by which plants respond to UV radiation? Ecological experiments can have other objectives, e.g. (1) does UV radiation in sunlight affect plant fitness? (2) does a differential effect of UV radiation between plant species affect the outcome of competition? (3) does the exposure to UV radiation alter plant-pathogen and plant-herbivore interactions? Finally applied research related to agricultural and horticultural production and produce is based on questions like: (1) can manipulations of UV radiation be used to manage produce quality? (2) can manipulation of UV radiation replace the use of pesticides and growth regulators? The approach suitable for a given experiment will depend on its objectives. When doing experiments with terrestrial plants, the medium surrounding the stems and leaves is air. At short path lengths air has little influence on UV irradiance and only when considering the whole depth of the atmosphere, its UV transmittance needs to be taken into account. In contrast, water and impurities like dissolved organic matter (DOM) absorb UV radiation over relatively short path lengths, which means that in water bodies UV irradiance decreases with depth. Basic concepts of photobiology, radiation physics and UV in the natural environment of plants are discussed in chapter 1. Varied approaches are used in the study of the effects of UV radition on plants. The main dichotomy is whether (1) UV radiation is added by means of special lamps to either sunlight or to visible light from other lamps, or (2) UV radiation in sunlight is excluded or attenuated by means of filters. Both approaches are extensively discussed in chapter 2. For any experimental approach used in UV research we need to quantify UV radiation and express it as meaningful physical quantities that allow comparison among experiments and to natural conditions. When comparing UV irradiance from sources differing in spectral composition, the comparison requires the calculation of biologically effective doses. Quantification of UV radiation is discussed in chapter 3. The appendices present in detail the calculations needed when measuring action spectra, and for calculating biologically effective UV doses both with Excel and R. An R package which facilitates such calculations accompanies this handbook, and will be made available through CRAN (the Comp