Changes of carbon and nitrogen metabolites in white spruce (Picea glauca [Moench] Voss) of contrasted growth phenotypes

The present study documents the changes occurring at the biochemical level in white spruce trees (Picea glauca Moench] Voss) with contrasted growth phenotypes during the summer period. Full-siblings of tall versus small spruces were grown under controlled conditions at constant day/night temperatures (24/15°C) and exposed to a decreasing photoperiod (15.7–12.2 h) simulating natural photoperiod reduction during the summer in eastern Canada. Growth parameters (stem height and tree biomass) were determined and non structural carbohydrates, soluble proteins and amino acids were quantified in current-year needles and stem, oldest stem and roots from mid-July until the end of September 2006. Sucrose was the main soluble sugar found in all organs, but its concentrations did not significantly change during the summer. In contrast, starch concentrations rapidly declined by the end of the experiment, especially in needles and stems. Both sucrose and starch did not generally differ between growth phenotypes. Total soluble protein significantly accumulated by mid-August (14.4 h of photoperiod) in small trees. Arginine and glutamine were the most abundant amino acids found in spruce organs, and their concentrations strongly increased at 14.4 h of photoperiod, especially in small trees. Our results highlight marked differences in nitrogen metabolism in late summer between contrasted growth phenotypes, especially for arginine, an amino acid typically associated with growth arrest and nitrogen reserve in perennial species. They also reveal that old stems and roots are important storage organs of organic reserves.