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

A continuous dual (CO2)-C-13 and (NH4NO3)-N-15-N-15 labelling experiment wa s undertaken to determine the effects of ambient (350 mu mol mol(-1)) or el evated (700 mu mol mol(-1)) atmospheric CO2 concentrations on C and N uptak e and allocation within 3-year-old beech (Fagus sylvatica L.) during leafin g, After six weeks of growth, total carbon uptake was increased by 63 % (ca lculated 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 ambie nt [CO2], Under ambient [CO2] 37 %, and under elevated [CO2] 51 %, of the l ignin C of the leaves derived from new assimilates. For both treatments, in ternal 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 t he C/N ratio of the new C and N uptake was increased by 32% under elevated [CO2].