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PubMed1995

Response of magnesium-deficient saplings in a young, open stand of Picea abies (L.) Karst. to elevated soil magnesium, nitrogen and carbon.

A decline in a Picea abies L. (Karst.) stand in the Fichtelgebirge, NE-Bavaria, FRG has been attributed to a nutritional disharmony-a seasonal imbalance between a high supply of nitrogen, caused by high nitrogen deposition, and a low supply of soil magnesium, caused by soil acidification (Oren et al., 1988a). The nutritional disharmony hypothesis was tested on ten-year-old P. abies saplings in an adjacent stand growing on identical soil. The supply rate of magnesium relative to nitrogen was continuously increased or decreased during three successive growing seasons. Increasing the nitrogen or carbon supply resulted in a small increase in foliar nitrogen concentrations. Magnesium or carbon addition slightly raised the concentration of magnesium in the foliage. Reduction in crown leaf-area did not result in any appreciable changes in nutrient concentrations. Increased N supply decreased foliar Mg concentrations. In spite of the changes in the nutritional status of the needles, gas-exchange rates, pigment concentrations, needle characteristics and growth of twigs and stems did not differ among treatments. It appears that the growth of saplings was unimpaired at the foliar magnesium concentration at which the growth of adjacent mature trees was reduced. Moreover, it was not possible to promote nutritional disharmony in the saplings, including those receiving three times the annual nitrogen input. The study demonstrates that in young, relatively open stands of P. abies, much of the deposited nitrogen is not absorbed by the roots of saplings. Thus, the conceptual model of nutritional disharmony cannot explain forest decline if nitrogen uptake does not increase with deposition. Identifying the processes which control the uptake relative to the supply of all nutrients, and quantifying the rates of nutrient uptake are essential steps in using the conceptual model to explain specific decline symptoms.

Journal Article↗
PubMed1975

Changes in cellular composition during magnesium deficiency.

Mg deficiency increased the water content of the liver, kidney, heart and thigh muscle in the rat and decreased the proportion of nitrogen in the dry matter of the same tissues. Changes in the concentration of metals also occurred. 2. Cellular fractional indicated that the Mg and K depleted in liver occurred primarily in the heavy-mitochondrial and microsomal fractions respectively. The calcification of liver and kidney was due to preferential deposition of Ca in the heavy-mitochondrial fraction. 3. The proportion of cellular nitrogen present in the heavy-mitochondrial and microsomal fractions was markedly decreased in the liver and kidney of the Mg-deficient rats, and the proportion in the supernatant fraction increased. 4. Electron microscopy revealed that the cross-sectional areas of liver cells and all their mitochondria were decreased in Mg deficiency. The number of mitochondrial per cell was decreased even more severely and the average area of a mitochondrion was greater in deficient rats than in control animals. 5. The significance of these observations is discussed in relation to the location of the primary metabolic disturbance during Mg deficiency.

Animals↗
PubMed1992

Growth, thyroid function, and serum macromineral levels in magnesium-deficient chicks.

Growth and thyroid function were studied in Mg-deficient chicks. Dietary levels of 80 to 315 ppm Mg were compared with control levels of 578 to 787 ppm Mg. Signs of Mg deficiency appeared rapidly and acutely within 2 to 5 days at dietary levels of 250 to 260 ppm or lower. Growth and feed intake decreased progressively as the deficiency became more severe. Control chicks pair-fed with the deficient chicks gained significantly more weight. Serum Mg decreased at all levels of Mg below control, but at 260 and 315 ppm it returned to control values after 21 days on treatment. Serum Ca diminished only when dietary Mg was 250 ppm or less. Serum K increased in severely deficient chicks but decreased over time in milder deficiencies. Thyroid gland weights were unchanged. However, very young chicks fed a Mg-deficient diet had lower serum 3,5,3'-triiodothyronine (T3) whereas serum thyroxine (T4) was generally unaffected. Beyond 1 wk of age chicks that had prior access to a Mg-sufficient diet had low serum T4 levels whereas serum T3 was unchanged. Therefore, peripheral thyroid hormone metabolism is altered in a Mg deficiency, but this effect is dependent on the age at which the deficiency occurs.

Animals↗