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Characterisation of carbon partitioning in response to climate change

To quantify carbon allocation between short- and long-term pools in wood in response to elevated CO2 and N-fertilization, in P. nigra, carbon concentrations and stocks were quantified. Although elevated CO2, N-fertilization and season had significant tissue-specific effects on carbon partitioning to the fractions of structural carbon, soluble sugars and starch as well as to residual soluble carbon, the overall magnitude of these shifts was small. The major effect of elevated CO2 and N-fertilization was on biomass production, resulting in about 30% increases in above ground stocks of cell wall mass. Relative C-partitioning between mobile and immobile C-pools was not significantly affected by elevated CO2 or N-fertilization. These data demonstrate high metabolic flexibility of P. nigra to maintain C-homeostasis under changing environmental conditions.

To characterise secondary metabolites and internal N-pools responding to elevated CO2 and N-fertilization, carbon-based secondary compounds, concentrations of total N and Klason lignin-bound N were measured in P. nigra. Elevated CO2 had no influence on lignin, cell wall-bound phenolics and soluble condensed tannins. Higher N-supply slightly but markedly stimulated formation of carbon-based secondary compounds. Elevated CO2 decreased internal N-pools in wood, but external N-supply increased the internal N-pools. In wood, 17-26% of N was bound to Klason lignin probably forming a recalcitrant N-fraction. Neither elevated CO2 nor higher N-supply altered N-partitioning between lignin-bound N and other N-containing compounds. Positive correlations existed between the biosynthesis of proteins and secondary compounds in P. nigra. These data imply that the growth and defence of forest trees are well orchestrated.

Based on the above results, it is concluded that in future climate scenario negative effects on wood quality may be anticipated. However, non-structural carbon compounds can be utilized more rapidly for structural growth under elevated atmospheric CO2 in fertilized agro-forestry systems. The growth and defence of forest trees were homeostatically balanced even if increases in atmospheric [CO2] were accompanied by increased N availability.

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