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 r esulting from an annual mean reduction of 15% in the stratospheric ozo ne under UK field conditions, but taking account of seasonal variation in depletion. The effects of this enhanced level of UV-B on the growt h, physiology and yield of four cultivars of pea were assessed. Enhanc ed 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 sig nificant 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 part ly due to enhanced abscission of pods during the final month of plant growth. UV-B treatment had no significant effect on chlorophyll fluore scence characteristics or CO2 assimilation rate per unit leaf area. Th ese results are consistent with previous controlled environment experi ments, and suggest that reduction in yield may be due to direct effect s of UV-B on plant growth rather than a decrease in photosynthetic cap acity per unit leaf area.