© 1988 Heron Publishing—Victoria, Canada
Nitrate content, amino acid composition and growth of yellow birch seedlings in response to light and nitrogen source
H. A. Margolis (1) and L.-P. Vézina (2)
1. Départment des Sciences Forestières, Faculté de Foresterie et de Géodésie, Université Laval, Sainte-Foy, Québec, Canada G1K
7P4 / 2. Agriculture Canada Research Station, 2560 Hochelaga, Sainte-Foy, Québec, Canada G1V 2J3 / Received December 23, 1987
Summary
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 (NH4+), nitrate only (NO3–) and a 1:1 mixture of ammonium and nitrate (NH4+/NO3–)—in a completely randomized factorial design. The total biomass of seedlings grown under low light (LL) did not vary significantly
with nitrogen source; although NO3–-treated seedlings were smaller and had a significantly lower (P ≤ 0.05) net assimilation rate (NAR) than NH4+-, and NH4+/NO3–-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 NO3– or NH4+/NO3–. Under LL, nitrate concentrations in xylem sap and leaves of plants grown with NO3– or NH4+/NO3– were many times greater than under FL. Amino acid profiles were affected by nitrogen source but were not affected by radiant
flux density. When NH4+-N was absent from the nutrient solution, the percentage of NH2-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 NO3– in roots, rather than the later stages of amino acid synthesis, that is limited by light in yellow birch seedlings.
