© 1997 Heron Publishing—Victoria, Canada
Histology of magnesium-deficient Norway spruce needles influenced by nitrogen source
Laurence Puech and Beate Mehne-Jakobs
Institute of Forest Botany and Tree Physiology, Albert-Ludwigs-University, Bertoldstrasse 17, D-79085 Freiburg, Germany / Received July 6, 1995
Summary
Effects of magnesium deficiency and variation in nitrate to ammonium ratio on needle histology and chlorophyll concentration
were investigated in current-year and one-year-old needles of clonal Norway spruce trees (Picea abies (L.) Karst.). Six-year-old trees were grown for one year in sand culture with circulating nutrient solutions containing a
sufficient (0.2 mM) or a limiting (0.04 mM) concentration of Mg. The nitrogen concentration was not varied (5 mM), but the
NO3–/NH4+-ratio was adjusted to 0.76 in Mg-sufficient and to 1.86, 0.76 or 0.035 in Mg-limited plants. Visible symptoms of Mg deficiency
occurred only in current-year needles, indicating adequate Mg nutrition before the experiment. Under conditions of Mg limitation,
chlorophyll and Mg concentrations were lowest in needles of trees supplied with NH4+ as the major nitrogen source and highest in needles of trees supplied with NO3– as the major nitrogen source. In current-year and one-year-old needles, starch accumulation induced by Mg deficiency was
increased when NH4+ was the major nitrogen source. The accumulation of tannin spherules in current-year needles, which occurred in response to
Mg deficiency, also increased with decreasing NO3–/NH4+-ratios. Deficient Mg supply caused premature aging in tissues of the vascular bundle, as indicated by modifications of the
cambium and increased amounts of collapsed sieve cells. The number of collapsed sieve cells was slightly lower in needles
grown in a NH4+-dominated nutrient regime than in needles grown in a NO3–-dominated nutrient regime. We conclude that was not directly toxic to Norway spruce trees at the applied concentrations.
However, effects of Mg deficiency were considerably greater in an NH4+-dominated nutrient regime than in a NO3–-dominated nutrient regime.
Keywords:
chlorophyll, magnesium deficiency, needle histology, Picea abies, starch accumulation.
