Carbon and nitrogen allocation patterns of Douglas-fir seedlings fertilized with nitrogen in autumn. I. Overwinter metabolism

Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) seedlings at a western Oregon nursery were fertilized in October 1983 with ammonium nitrate and harvested for biochemical analyses on four dates over autumn and winter 1983–1984. Free amino acid and total nitrogen concentrations in the needles of fertilized seedlings showed a pronounced increase 1 month after fertilization. Free amino acid concentrations of fertilized seedlings decreased in needles during winter but remained stable in stems and fine roots. Just before budbreak in mid-March, free amino acid concentrations increased significantly in stems and fine roots. Total nitrogen concentrations increased 1 month after fertilization, remained stable throughout winter, and tended to decrease or remain stable just before budbreak. Starch and total nonstructural carbohydrate concentrations of needles and stems of fertilized seedlings were lower just before budbreak and sugar concentrations of fine roots of fertilized seedlings were lower when data from all harvests were combined. The reduction in carbohydrate reserves following fertilization probably reflects increased respiration associated with the synthesis and maintenance of higher levels of enzymes.