Elevated CO2 does not ameliorate effects of ozone on carbon allocation in Pinus halepensis and Betula pendula in symbiosis with Paxillus involutus

The effect of 700 mu mol CO2 mol(-1), 200 mmol ozone mol(-1) and a combinat ion of the two on carbon allocation was examined in Pinus halepensis co-cul tured with Betula pendula in symbiosis with the ectomycorrhizal fungus Paxi llus involutus, The results show that under low nutrient and ozone levels, elevated CO2 has no effect on the growth of B. pendula or P. halepensis see dlings nor on net carbon partitioning between plant parts. Elevated CO2 did not enhance the growth of the fungus in symbiosis with the birch, On the o ther hand, ozone had a strong negative effect on the growth of the birch, w hich corresponded with the significantly reduced growth rates of the fungus . Exposure to elevated CO2 did not ameliorate the negative effects of ozone on birch; in contrast, it acted as an additional stress factor. Neither oz one nor CO2 had significant effects on biomass accumulation in the pine see dlings, Ozone stimulated the spread of mycorrhizal infection from the birch seedlings to neighbouring pines and had no statistically significant effec ts on phosphoenolpyruvate carboxylase (PEPC) or ribulose-1,5-bisphosphate c arboxylase/oxygenase (Rubisco) activity in the pine needles or on PEPC acti vity in pine roots.