Manganese deficiency in plants
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Manganese Deficiency in Plants: Impacts and Management
Importance of Manganese in Plant Physiology
Manganese (Mn) is a crucial micronutrient for plants, playing a vital role in various physiological processes. It is an essential cofactor in the oxygen-evolving complex (OEC) of photosystem II (PSII), which is critical for the water-splitting reaction during photosynthesis . Mn also supports metabolic functions such as glycosylation, reactive oxygen species (ROS) scavenging, and overall photosynthetic efficiency.
Symptoms and Effects of Manganese Deficiency
Photosynthetic Impairment
Manganese deficiency significantly impacts photosynthetic processes. It destabilizes PSII, leading to reduced photosynthetic efficiency and photoinhibition . In Scots pine seedlings, Mn deficiency suppressed growth and decreased the content of photosynthetic pigments, although it increased the expression of photosynthetic genes.
Growth and Reproductive Issues
Mn deficiency can lead to visible symptoms such as chlorosis and poor growth. In maize, Mn deficiency resulted in poor tasseling, delayed anther development, and reduced pollen viability, which in turn affected seed setting and development. Similarly, in bush beans, Mn deficiency enhanced sensitivity to ozone toxicity, further stressing the plants.
Root Adaptations
Mn deficiency also affects root physiology. In barley, the intensity of Mn deficiency altered the suberization of endodermal cells, impacting ion homeostasis and transport. Mild deficiency increased the length of the unsuberized zone near the root tip, while severe deficiency increased suberization closer to the root tip.
Soil and Environmental Factors
Soil pH and Composition
Mn deficiency is prevalent in dry, well-aerated, and calcareous soils, as well as soils with high organic matter content, where Mn bioavailability is low . Soils with a pH of 6.7 or higher, especially heavily limed sandy podsols, are particularly prone to Mn deficiency. Weather conditions and cultural practices, such as liming, can exacerbate Mn deficiency by making the soil more alkaline.
Geographic Distribution
The occurrence of Mn deficiency is influenced by various edaphic, climatic, plant, and managerial factors. It is a widespread issue in many parts of the world, affecting crop productivity significantly.
Management and Correction
Soil Testing and Amendments
To prevent and correct Mn deficiency, it is essential to test soil Mn levels before applying lime, especially in sandy soils. The "manganese value" formula, which measures exchangeable Mn, can help determine the allowable increase in soil pH without risking Mn deficiency. Adding Mn sulfate to the soil or as a foliar spray can effectively prevent and treat Mn deficiency, as demonstrated in crops like oats and sugar cane.
Plant Breeding and Genetic Approaches
Some plant genotypes exhibit differential tolerance to Mn deficiency, enabling them to grow on marginal lands with poor Mn availability. Understanding and utilizing these genotypes can help develop Mn-efficient crops.
Conclusion
Manganese is an essential micronutrient for plant growth and development, with significant roles in photosynthesis and metabolic processes. Mn deficiency can severely impact plant health, leading to reduced growth, impaired photosynthesis, and reproductive issues. Soil composition, pH, and environmental conditions play crucial roles in Mn availability. Effective management strategies, including soil testing, amendments, and breeding Mn-efficient crops, are vital for mitigating Mn deficiency and ensuring optimal plant productivity.
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