Effects of enhanced UV-B radiation on pea (Pisum sativum L.) grown under field conditions in the UK

A new modulated lamp system is described. This system has successfully provided an ultraviolet-B (UV-B) supplement in proportion to ambient UV-B. The modulated system was used to simulate the UV-B environment resulting from an annual mean reduction of 15% in the stratospheric ozone under UK field conditions, but taking account of seasonal variation in depletion. The effects of this enhanced level of UV-B on the growth, physiology and yield of four cultivars of pea were assessed. Enhanced UV-B resulted in small reductions in the number of stems and total stem length per plant (respectively 4.7 and 8.7%). There were also significant decreases in the dry weight of peas (10.1%), pods (10.3%) and stems (7.8%) per plant. UV-B treatment had no effect on the number of peas per pod or average pea weight, but did significantly reduce (12.1%) the number of pods per plant. This decrease in pod number was partly due to enhanced abscission of pods during the final month of plant growth. UV-B treatment had no significant effect on chlorophyll fluorescence characteristics or CO₂assimilation rate per unit leaf area. These results are consistent with previous controlled environment experiments, and suggest that reduction in yield may be due to direct effects of UV-B on plant growth rather than a decrease in photosynthetic capacity per unit leaf area.