Fungal species-specific responses of ectomycorrhizal Scots pine (Pinus sylvestris) to elevated [CO2]

Ectomycorrhizal seedlings of Scots pine (Pinus sylvestris) inoculated with the nitrotolerant Laccaria bicolor and the nitrophobic Suillus bovinus were exposed to ambient (350 mu l 1(-1)) and elevated (700 mu l 1(-1)) [CO2]. After 79 d the seedlings were labelled for 28 d with (CO2)-C-14, after which they were harvested. C-14 was determined in shoots, roots plus mycorrhizas, soil, and below-ground respiration; nitrogen was determined in shoots and roots. Total net C-14 uptake increased under elevated [CO2]. The extra carbon did not increase the shoot mass but was translocated to the roots and resulted in a decreased shoot-to-root ratio in the Suillus-inoculated seedlings. Laccaria-inoculated seedlings did not incorporate the additional carbon in root or fungal tissue but only increased below-ground respiration. S. bovinus acquired or transferred nitrogen better than L. bicolor and enabled the seedlings to perform better with regard to net carbon uptake under elevated [CO2]. This resulted in nitrogen concentrations in shoots of Suillus-inoculated seedlings that were twice as high as in Laccaria-inoculated seedlings, irrespective of [CO2]. The higher nitrogen concentration in the shoots resulted in a doubling of the C-14 uptake per unit shoot mass. Our results suggest that the ability of ectomycorrhizal Scots pine seedlings to respond positively to elevated atmospheric [CO2] is strongly fungal-species specific.