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Updated: Aug 26, 2026

Microplot Design and Plant and Soil Sample Preparation for 15Nitrogen Analysis
Published on: May 10, 2020
Nitrate content, amino acid composition and growth of yellow birch seedlings in response to light and nitrogen source
1Départment des Sciences Forestières, Faculté de Foresterie et de Géodésie, Université Laval, Sainte-Foy, Québec, Canada G1K 7P4.
Abstract:
Yellow birch (Betula alleghaniensis Britt.) seedlings were grown for three months in a greenhouse at two radiant flux densities-full light (FL) and 50% shade (LL)-and with three nitrogen sources- ammonium only (NH(4) (+)), nitrate only (NO(3) (-)) and a 1:1 mixture of ammonium and nitrate (NH(4) (+)/NO(3) (-))-in a completely randomized factorial design. The total biomass of seedlings grown under low light (LL) did not vary significantly with nitrogen source; although NO(3) (-)-treated seedlings were smaller and had a significantly lower (P = 0.05) net assimilation rate (NAR) than NH(4) (+)-, and NH(4) (+)/NO(3) (-)-N-treated seedlings. Under full light (FL), NW-treated seedlings had a lower leaf area ratio (LAR) and a significantly lower total biomass and relative growth rate (RGR) than seedlings grown with either NO(3) (-) or NH(4) (+)/NO(3) (-). Under LL, nitrate concentrations in xylem sap and leaves of plants grown with NO(3) (-) or NH(4) (+)/NO(3) (-) were many times greater than under FL. Amino acid profiles were affected by nitrogen source but were not affected by radiant flux density. When NH(4) (+)-N was absent from the nutrient solution, the percentage of NH(2)-N carried in the xylem sap decreased for aspartic acid but increased for alanine and glycine. The results indicate that it is the initial reduction of NO(3) (-) in roots, rather than the later stages of amino acid synthesis, that is limited by light in yellow birch seedlings.
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