The effect of elevated [CO2] on uptake and allocation of 13C and 15N in beech (Fagus sylvatica L.) during leafing

A continuous dual (CO2)-C-13 and (NH4NO3)-N-15-N-15 labelling experiment was undertaken to determine the effects of ambient (350 mu mol mol(-1)) or elevated (700 mu mol mol(-1)) atmospheric CO2 concentrations on C and N uptake and allocation within 3-year-old beech (Fagus sylvatica L.) during leafing, After six weeks of growth, total carbon uptake was increased by 63 % (calculated on total C content) under elevated CO2 but the carbon partitioning was not altered. 56 % of the new carbon was found in the leaves. On a dry weight basis was the content of structural biomass in leaves 10 % lower and the lignin content remained unaffected under elevated as compared to ambient [CO2], Under ambient [CO2] 37 %, and under elevated [CO2] 51 %, of the lignin C of the leaves derived from new assimilates. For both treatments, internal N pools provided more than 90 % of the nitrogen used for leaf-growth and the partitioning of nitrogen was not altered under elevated [CO2]. The C/N ratio was unaffected by elevated [CO2] at the whole plant level, but the C/N ratio of the new C and N uptake was increased by 32% under elevated [CO2].