The effects of nitrogen fertilisation and elevated CO2 on the lipid biosynthesis and carbon isotopic discrimination in birch seedlings (Betula pendula)

The effects of nitrogen (N) fertilisation and elevated [CO2] on lipid biosy nthesis and carbon isotope discrimination in birch (Betula pendula Roth.) t ransplants were evaluated using seedlings grown with and without N fertilis er, and under two concentrations of atmospheric CO2 (ambient and ambient+25 0 mu mol mol(-1)) in solar dome systems. N fertilisation decreased n-fatty acid chain length (18:0/16:0) and the ratios of alpha-linolenate (18:2)/lin oleate (18:1), whereas elevated [CO2] showed little effect on n-fatty acid chain length, but decreased the unsaturation (18:2+18:1)/18:0. Both N ferti lisation and elevated [CO2] increased the quantity of leaf wax n-alkanes, w hilst reducing that of n-alkanols by 20-50%, but had no simple response in fatty acid concentrations. C-13 enrichment by 1-2.5% under N fertilisation was observed, and can be attributed to both reduced leaf conductance and in creased photosynthetic consumption of CO2. Individual n-alkyl lipids of dif ferent chain length show consistent pattern of delta(13)C values within eac h homologue, but are in general 5-8% more depleted in C-13 than the bulk ti ssues. Niether nitrogen fertilisation and elevated CO2 influenced the relat ionship between carbon isotope discrimination of the bulk tissue and the in dividual lipids.