Uses of biological spectral weighting functions and the need of scaling for the ozone reduction problem

Abstract

In several phases of assessing implications of stratospheric ozone reduction for plants, biological spectral weighting functions (BSWF) play a key role: calculating the increase of biologically effective solar ultraviolet-B radiation (UV-B_BE) due to ozone reduction, assessing current latitudinal gradients of UV-B_BE, and comparing solar UV-B_BE with that from lamps and filters in plant experiments. Plant UV action spectra (usually determined with monochromatic radiation in the laboratory with exposure periods on the order of hours) are used as BSWF. Yet, many complicating factors cloud the realism of such spectra for plants growing day after day in polychromatic solar radiation in the field. The uses and sensitivity of BSWF in the stratospheric ozone reduction problem are described. The need for scaling BSWF from action spectra determined with monochromatic radiation in laboratory conditions over periods of hours to polychromatic solar radiation in the field is developed. Bottom-up mechanistic and top-down polychromatic action spectrum development are considered as not satisfactory to resolve realistic BSWF. A compromise intermediate approach is described in which laboratory results are tested under polychromatic radiation in growth chambers and, especially, under field conditions. The challenge of the scaling exercise is to resolve disagreements between expected spectral responses at different scales of time and radiation conditions. Iterative experiments with feedback among the different experimental venues is designed to reduce uncertainties about realistic BSWF in the field. Sensitivity analyses are employed to emphasize characteristics of BSWF that are particularly important in assessing the ozone problem. Implications for use of realistic BSWF both for improved research design and for retrospective analysis of past research is described.