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]. A fter 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 car bon did not increase the shoot mass but was translocated to the roots and r esulted in a decreased shoot-to-root ratio in the Suillus-inoculated seedli ngs. Laccaria-inoculated seedlings did not incorporate the additional carbo n 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 ele vated [CO2]. This resulted in nitrogen concentrations in shoots of Suillus- inoculated seedlings that were twice as high as in Laccaria-inoculated seed lings, irrespective of [CO2]. The higher nitrogen concentration in the shoo ts resulted in a doubling of the C-14 uptake per unit shoot mass. Our resul ts suggest that the ability of ectomycorrhizal Scots pine seedlings to resp ond positively to elevated atmospheric [CO2] is strongly fungal-species spe cific.