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

Abstract

Ectomycorrhizal seedlings of Scots pine (Pinus sylvestris) inoculated with the nitrotolerant Laccaria bicolor and the nitrophobic Suillus bovinus were exposed to ambient (350 l l1) and elevated (700 l l1) [CO2]. After 79 d the seedlings were labelled for 28 d with 14CO2, after which they were harvested. 14C was determined in shoots, roots plus mycorrhizas, soil, and below-ground respiration; nitrogen was determined in shoots and roots. Total net 14C 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 14C 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.