Introduction

There are four main ways in which radiation is important for plant life:

1. Thermal effects. Radiation is the major mode of energy exchange between plants and the aerial environment: solar radiation provides the main energy input to plants, with much of this energy being converted to heat and driving other radiation exchanges and processes such as transpiration, as well as being involved in determining tissue temperatures with consequences for rates of metabolic processes and the balance between them (see particularly Chapters 5 and 9).

2. Photosynthesis. Some of the solar radiation absorbed by plants is used to generate ‘energy-rich’ compounds that can drive energy-requiring (endergonic) biochemical reactions. These energy-rich compounds include those derived by dehydration (e.g. in the reaction of inorganic phosphate and ADP to form ATP) or reduction (e.g. of NADP+ to NADPH). This harnessing of the energy in solar radiation in photosynthesis is characteristic of plants and provides the main input of free energy into the biosphere (see Chapter 7).

3. Photomorphogenesis. The amount, direction, timing and spectral distribution of shortwave radiation also plays an important role in the regulation of growth and development (see Chapter 8).

4. Mutagenesis. Very shortwave, highly energetic radiation, including the ultraviolet, as well as X- and γ-radiation, can have damaging effects on living cells, particularly affecting the structure of the genetic material and causing mutations.