NUTRITION DETERMINES THE STRATEGY OF BETULA-PENDULA FOR COPING WITH OZONE STRESS

Cuttings of Betula pendula were exposed to O-3-free air (control) or 9 0/40 nl O-3 1(-1) (day/night) and to high and low supply of macro/micr o-nutrients throughout the growing season. O-3 uptake was similar in b oth nutrient regimes, but in the high-fertilized (HF) plants both form ation rate and O-3-induced shedding of leaves was increased relative t o the low fertilized (LF) plants under O-3 exposure. O-3-exposed leave s in LF plants approached life spans similar to the LF control. Only l eaves of O-3-exposed LF plants displayed distinct increases in the con centrations of sugars and reduced ascorbate, in PEP carboxylase activi ty and delta(13)C, but the water-use efficiency (WUE) declined and was accompanied by elevated dark respiration, similar to HF plants under O-3 stress. O-3-exposed HF plants based their carbon gain on the new i ntact leaves, while the foliage area stayed reduced (loss of ageing O- 3-injured leaves, suppressed branch formation) as compared with the HF control. In contrast, the O-3-exposed LF plants maintained their foli age area similar to the LF control, although the carbon gain was gover ned by the O-3-injured leaves. Whole-plant production was overall dete rmined by nutrition, however, both 'strategies' in leaf turn-over were similarly efficient in limiting the proportional O-3-caused reduction in biomass production relative to the corresponding LF and HF control s. However, the O-3-exposed LF plants distinctly altered carbon alloca tion towards a low root/shoot biomass ratio (RIS), whereas the LF cont rol displayed rather high RIS. The carbon balance of O-3-exposed plant s displayed high respiratory costs at low nutrient supply and low WUE (biomass increment/whole-plant transpiration) regardless of nutrition.