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UV-B dose responses of two lines of pea were quantified at 2.3, 4.6, 6.9 and 9.2 kJ m(-2) day(-1) W-B (weighted according to Caldwell's generalised plant action spectrum) in controlled environments providing near-field doses of photosynthetic radiation. Increasing UV-B significantly increased UV-B absorbing compounds in both lines. In the UV-B sensitive line, JI1389, increasing UV-B significantly inhibited most aspects of plant morphology and biomass. In the more UV-B-tolerant line, Scout, increasing UV-B significantly reduced foliage area but had no effect on above-ground biomass. although root biomass was significantly increased. Reduced plant height in JI1389 was caused by shorter internodes, in turn due to reduced cell number but not cell length. UV-B had no significant effects on photosynthesis in either line. Significant dose responses were linear for the growth of the main stem in JI1389 but remaining significant dose responses were better fitted by quadratics with maximum UV-B effects occurring in the range 5-7 kJ m(-2) day(-1) PAS300, due to stimulation of branch growth at the highest dose. However, growth stimulation by W-B was confined to PAS300 doses which at temperate latitudes would result only from rather extreme ozone depletions. We conclude that investigations using relatively low UV-B doses, rather than those well above the current maximum, may be the best approach to both understanding of the fundamental mechanisms of plant responses to UV-B and quantifying the magnitude of responses to stratospheric ozone depletion. |
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