*SOLAR UV AND THE ROLE OF ACTION SPECTRA IN ASSESSING THE 

 BIOLOGICAL CONSEQUENCES OF SOLAR UV-B RADIATION 



MARTYN M. CALDWELL 



Department of Range Science 



Utah State University 



Logan, UT 84322-5230 



♦Abstract taken from Caldwell, M.M., L.B. Camp, C.W. Warner, and S.D. Flint, 

 1986. Action spectra and their key role in assessing biological consequences of 

 solar UV-B radiation change. In, NATO ASI Series, Vol. G8: Stratospheric Ozone 

 Reduction, Solar Ultraviolet Radiation and Plant Life (R.C. Worrest and M.M. 

 Caldwell, eds.). Springer-Verlag, Berlin, pp. 87-111. 



ABSTRACT: Action spectra of UV damage to plants must be used as weighing 

 functions to (1) evaluate the relative increase of solar UV radiation that would 

 result from a decreased atmospheric ozone layer, the radiation amplification 

 factor--RAF, (2) evaluate the existing natural gradients of solar UV irradiance 

 on the earth, and (3) compare UV radiation from lamp systems in experiments with 

 solar UV radiation in nature. Only if the relevant biological action spectra 

 have certain characteristics is there a potential biological problem that would 

 result from ozone reduction. Similarly the existence of a natural latitudinal 

 solar UV gradient is dependent on action spectrum characteristics. 



Several UV action spectra associated with different basic modes of damage to 

 plant tissues all have the common characteristic of decreasing effect with 

 increasing wavelength; however, the rate of decline varies considerably. 

 Extrapolation from action spectra that have been measured on isolated organelles 

 and microorganisms using monochromatic radiation to effects of polychromatic 

 radiation on intact higher plants is precarious. Development of action spectra 

 using polychromatic radiation and intact higher plant organs can yield spectra 

 that are of more ecological relevance for weighing factors in assessment of the 

 ozone reduction problem. An example of an action spectrum for photosynthetic 

 inhibition developed with polychromatic radiation is provided in this chapter. 

 This action spectrum has different characteristics, and results in a greater RAF 

 than do action spectra for inhibition of a partial photosynthetic reaction, the 

 hill reaction, developed with isolated chloroplast and photosynthetic bacteria. 

 Circumstantial evidence from experiments with plants originating from different 

 latitude also supports the notion that action spectra with characteristics 

 similar to that of the provisional spectrum, developed with polychromatic 

 radiation, are appropriate. Further work with polychromatic radiation is 

 encouraged. 



There are two basic types of error that are associated with the use of action 

 spectra in biological assessments of the ozone reduction problem, the RAF errors 

 and the enhancement errors. The former are those associated with calculation of 

 the RAF, and the latter are those derived from calculation of the UV radiation 

 enhancement used in experiments with lamp systems. While the RAF errors are 

 recognized, the enhancement errors have not been generally appreciated. An error 

 analysis is presented showing that the enhancement errors will typically be 

 larger and in the opposite direction than the RAF errors. The enhancement error 



