title: Do elevation of CO(2) concentration and nitrogen fertilization alter storage and remobilization of carbon and nitrogen in pedunculate oak saplings?
abstract: Soil nitrogen can alter storage and remobilization of carbon and nitrogen in forest trees and affect growth responses to elevated carbon dioxide concentration ([CO(2)]). We investigated these effects in oak saplings (Quercus robur L.) exposed for two years to ambient or twice ambient [CO(2)] in combination with low- (LN, 0.6 mmol N l(-1)) or high-nitrogen (HN, 6.1 mmol N l(-1)) fertilization. Autumn N retranslocation efficiency from senescing leaves was less in HN saplings than in LN saplings, but about 15% of sapling N was lost to the litter. During the dormant season, nonstructural carbohydrates made up 20 to 30% of the dry mass of perennial organs. Starch was stored mainly in large roots where it represented 35-46% of dry mass. Accumulation of starch increased in large roots in response to LN but was unaffected by elevated [CO(2)]. The HN treatment resulted in high concentrations of N-soluble compounds, and this effect was reduced by elevated [CO(2)], which decreased soluble protein N (-17%) and amino acid N (-37%) concentrations in the HN saplings. Carbon and N reserves were labeled with (13)C and (15)N, respectively, at the end of the first year. In the second year, about 20% of labeled C and 50% of labeled N was remobilized for spring growth in all treatments. At the end of leaf expansion, 50-60% of C in HN saplings originated from assimilation versus only 10-20% in LN saplings. In HN saplings only, N uptake occurred, and some newly assimilated N was allocated to new shoots. Through effects on the C and N content of perennial organs, elevated [CO(2)] and HN increased remobilization capacity, thereby supporting multiple shoot flushes, which increased leaf area and subsequent C acquisition in a positive feedback loop.
authors.affiliation: Génomique Ecophysiologie et Ecologie fonctionnelles, 54506 Vandoeuvre, France.
authors.forename: Seraphine
authors.initials: S
authors.lastname: Vizoso
authors.forename: Dominique
authors.initials: D
authors.lastname: Gerant
authors.forename: Jean Marc
authors.initials: JM
authors.lastname: Guehl
authors.forename: Richard
authors.initials: R
authors.lastname: Joffre
authors.forename: Michel
authors.initials: M
authors.lastname: Chalot
authors.forename: Patrick
authors.initials: P
authors.lastname: Gross
authors.forename: Pascale
authors.initials: P
authors.lastname: Maillard