A STUDY OF THE TOTAL ULTRAVIOLET EXPOSURE TO ALL THE LEAVES FOR SMALL-PLANT GROWTH

A dosimetric spectrum evaluator has been employed to evaluate the tota l biologically effective UV (UVBEplant) incident on the surface of all the leaves of small plants. It is applied to evaluate the UVBEplant t o soybean leaves (Glycine mar [L.] Merr.), cultivar Essex. The plants receive three levels of UVBEplant averaged over all the leaves (0, 8.1 and 15.8 J cm(-2)) from emergence to the V7 growth stage. As canopy c losure occurs with plant growth, the ratio of the average of the UVBEp lant to all leaves compared to that on the uppermost set of leaves cha nges from 0.85 to 0.50 to 0.29 for the V2, V4 and V7 stages, respectiv ely. Measurement of the UVBEplant at the top of the canopy will introd uce errors of 18, 100 and 245% at the V2, V4 and V7 stages, respective ly, compared to the actual exposure to the plant leaves. The evaluatio n of leaf UVBEplant allows formulation of models defining plant respon se, such as suppression of plant height and leaf area in terms of the UV exposure to all the leaves along with the effects on the fresh and dry weights of the leaves, stems and roots. (C) 1998 Elsevier Science S.A. All rights reserved.