ABSTRACT
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 NO(3) (-)/NH(4) (+)-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 NH(4) (+) as the major nitrogen source and highest in needles of trees supplied with NO(3) (-) as the major nitrogen source. In current-year and one-year-old needles, starch accumulation induced by Mg deficiency was increased when NH(4) (+) 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 NO(3) (-)/NH(4) (+)-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 NH(4) (+)-dominated nutrient regime than in needles grown in a NO(3) (-)-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 NH(4) (+)-dominated nutrient regime than in a NO(3) (-)-dominated nutrient regime.
ABSTRACT
Both short- and long-term effects of Mg deficiency on carbohydrate metabolism were investigated in 6-year-old clonal Norway spruce (Picea abies (L.) Karst.) trees cultivated in sand culture with an optimal supply of nutrients, except for Mg which was supplied at 0.203, 0.041 and 0.005 mM to provide optimal, moderately deficient and severely deficient Mg supply, respectively. Annual changes in carbohydrate concentrations (starch, sucrose, glucose and fructose) were analyzed and diurnal changes were investigated on a single day during the summer. Older needles of trees in the moderate Mg-deficiency treatment developed tip-yellowing symptoms, whereas current-year needles remained green. The severe Mg-deficiency treatment led to pronounced yellowing symptoms in needles of all ages. Increased carbohydrate concentrations were observed before needle yellowing occurred. Diurnal and annual changes in carbohydrates were similar in all treatments; however, carbohydrate concentrations were influenced by Mg supply. In both Mg-deficiency treatments, starch concentrations increased in needles, especially during summer and autumn. Starch accumulation was more pronounced at the beginning of the Mg-deficiency treatments than at the end of the treatments. Sucrose, and to a minor extent, glucose and fructose concentrations tended to increase in response to Mg deficiency. The consequences of Mg deficiency on carbohydrate metabolism are discussed with respect to reduced plant growth and decreased transport rates of carbohydrates to sink organs.
