Solar ultraviolet radiation exclusion increases soybean internode lengths and plant height

Soybean [Glycine max (L.) Merr.] cultivars Williams-82 and Maverick were grown in a polycarbonate greenhouse (P-GH), a glass greenhouse (G-GH), and outdoors during daytime (control) to investigate the effect of (i) exclusion of both ultraviolet B (UV-B, 280-320 nm) and ultraviolet A (UV-A, 320-400 nm), (ii) exclusion of UV-B only, and (iii) exposure to daytime solar UV radiation (09:00-17:00 h local time daily). Both the P-GH and the G-GH were maintained at day/night air temperatures of 30/22 °C. The purpose was to quantify the growth differences due to partial and total UV exclusion compared with the control. Exclusion of both UV-B and UV-A radiation caused elongated internodes on the plants, which resulted in greater plant height. Mean mainstem length of Williams-82 was 50.2 cm for the control, but they were 45% and 237% greater for excluded UV-B radiation only and both excluded UV-B and UV-A radiation, respectively. Similarly, mean mainstem length of Maverick was 55.2 cm for the control, but they were 52% and 198% greater for excluded UV-B only and both excluded UV-B and UV-A, respectively. There also was a slight increase in the number of nodes with increasing extent of UV radiation exclusion. The mean final V-stage of Williams-82 was 14.2 for the control, but they were 11% and 18% greater for excluded UV-B only and both excluded UV-B and UV-A, respectively. Likewise, the mean final V-stage of Maverick was 14.5 for the control, but they were 12% and 22% greater for excluded UV-B only and both excluded UV-B and UV-A, respectively. With exclusion of both UV-B and UV-A, pod yield for the Maverick cultivar was greater but this effect was not as clear for the Williams-82 cultivar. In summary, most of the total UV-exclusion effects were due to the exclusion of the UV-A radiation component. Finally, UV spectral transmission of greenhouse or controlled environment covering material should be considered before conducting research on plants, or producing plants commercially, that are sensitive to UV exclusion, such as certain grain legumes or horticultural crops.