Environmental Causes of Deficiency Symptoms

Content

⇒	Historical Information
	⇒	Determination of Essentiality
⇒	Function in Plants
	⇒	Metabolic Processes
	⇒	Growth
	⇒	Fruit Yield and Quality
⇒	Diagnosis of Magnesium Status in Plants
	⇒	Symptoms of Deficiency and Excess
		-	Symptoms of Deficiency
		-	Symptoms of Excess
	⇒	Environmental Causes of Deficiency Symptoms
	⇒	Nutrient Imbalances and Symptoms of Deficiency
		-	Potassium and Magnesium
		-	Calcium and Magnesium
		-	Nitrogen and Magnesium
		-	Sodium and Magnesium
		-	Iron and Magnesium
		-	Manganese and Magnesium
		-	Zinc and Magnesium
		-	Phosphorus and Magnesium
		-	Copper and Magnesium
		-	Chloride and Magnesium
		-	Aluminum and Magnesium
	⇒	Phenotypic Differences in Accumulation
	⇒	Genotypic Differences in Accumulation
⇒	Concentrations of Magnesium in Plants
	⇒	Magnesium Constituents
		-	Distribution in Plants
		-	Seasonal Variations
		-	Physiological Aspects of Magnesium Allocation
	⇒	Critical Concentrations
		-	Tissue Magnesium Concentration Associations with Crop Yields
		-	Tabulated Data of Concentrations by Crops
⇒	Assessment of Magnesium in Soils
	⇒	Forms of Magnesium in Soils
	⇒	Sodium Absorption Ratio
	⇒	Soil Tests
	⇒	Tabulated Data on Magnesium Contents in Soils
		-	Soil Types
⇒	Fertilizers for Magnesium
	⇒	Kinds of Fertilizers
	⇒	Effects of Fertilizers on Plant Growth
	⇒	Application of Fertilizers
⇒	References

Conditions of the soil and rhizosphere such as drought or irregular water availability (63,64), poor drainage or excessive leaching (11), low soil pH (65-67), or cold temperatures (68,69) will exaggerate magnesium deficiency symptoms, as magnesium is not physically available under these environmental conditions or physiologically, the plant roots are not capable of absorbing adequate magnesium to sustain normal plant growth.

Conditions of the soil and rhizosphere such as drought or irregular water availability will impact magnesium uptake. In sugar maple (Acer saccharum Marsh.), foliar analysis indicated that magnesium deficiency occurred during drought (64). Likewise, Huang (63) reported that drought-stressed tall fescue (Festuca arundinacea Schreb.) had lower leaf magnesium concentrations than wellwatered fescue.

Low soil pH is also associated with a low supply or depletion of magnesium, possibly due to leaching; however, research suggests that impairment of root growth in acid soils (pH 4.3 to 4.7) also may hinder magnesium absorption (67). In one study (65), low soil pH (3.0) resulted in increased accumulation of magnesium in the shoots, but decreased accumulation in the roots. Contradicting Marler (65) and Tan et al. (67), Johnson et al. (70) found no clear correlation between low soil pH and magnesium accumulation.

Relatively high and low root-zone temperatures affect magnesium uptake, but the degree of impact may be influenced by plant type and stage of plant development. Huang et al. (71) and Huang and Grunes (68) reported that increasing root-zone temperature (10, 15, 20°C) linearly increased magnesium accumulation by wheat seedlings that were less than 30 days old but suppressed accumulation by seedlings that were more than 30 days old. Similarly, magnesium uptake decreased when temperatures in the rhizosphere decreased from 20 to 10°C (69).

Although any environmental condition such as unfavorable soil temperature or pH may reduce root growth and thus reduce magnesium uptake, other characteristics such as mycorrhizal colonization can increase magnesium uptake. Likewise, it has been shown that plants that have colonization of roots by mycorrhiza show higher amounts of magnesium accumulation relative to nonmycorrhizal plants (72–75).

Shoots exposed to environmental parameters such as high humidity (76), high light intensity (77,78), or high or low air temperatures (79) will decrease the ability of plants to absorb and translocate magnesium, since transpiration is reduced and the translocation of magnesium is driven by transpiration rates (63,76,80–84).

Light intensity can affect the expression of symptoms of magnesium deficiency. Partial shading of magnesium-deficient leaves has been shown to prevent or delay the development of chlorosis (77). Others (49,56) have also determined that magnesium deficiency symptoms may begin to appear only on the portions of a leaf or plant that are exposed to the sun, with the shaded portions of leaves remaining green. Zhao and Oosterhuis (78) also reported that shading (53% light reduction) increased leaf-blade concentrations of magnesium in cotton plants by 16% relative to unshaded plants.