Zinc (Zn) is one mineral or micronutrient that plants need in very minute amounts. This metal is naturally found in soil and water and is found throughout plant tissues, including leaves or fruits that humans and other animals consume. Problems arise when plants are both deprived of or are overexposed to zinc molecules, and the increased industrial mining or refuse of man-made products can disrupt natural amounts of zinc in soil and water.
The Role of Zinc in Plant Health
Zinc plays a central role in healthy plant metabolism and growth processes. Zinc is not needed in as large amounts as nitrogen, potassium or phosphorus. Molecules are absorbed by the roots and are transported in the vascular tissues in plants, which are called phloem and xylem, especially in conjunction with movement of nitrogen molecules. Zinc is needed for the creation of the plant growth hormone auxin and for creation of the green chlorophyll and cytochrome pigments. It also has a role in formation of enzymes and carbohydrates, regulation of starches and proper root development. Zinc also helps plants assimilate to cold temperatures across the growing season.
When soils are devoid of zinc molecules, physical changes manifest themselves on the plant. Soils that are arid, calcareous or highly weathered but acidic often have deficient zinc contents for healthy plant growth, as suggested by SprayGro. Michigan State University mentions that zinc deficiencies also are more common in soils that are neutral or alkaline in pH or are naturally rich in phosphorus. According to the University of Florida authors in "Your Florida Landscape," there are many visual cues on plants lacking adequate zinc. Young leaves may be yellowed or reduced in normal size (called "little leaf"), narrower than normal leaves with wavy edges or abnormally expanding and puckered. Another cue is what is called "rosetting"--space between new leaves is very small, and tiny leaves and shoots bunch up into a clustered tuft.
Overabundance of Zinc
According to the Dutch firm Lenntech, only a limited number of plants have a chance of survival in soils that are overly rich in zinc, such as those near mines or disposal sites with materials containing zinc. Abnormally high zinc levels in soils create a situation called heavy metal toxicity. The University of Michigan comments that higher zinc occurs in soils that are extremely acidic (pH below 5.0) or are fertilized with sewerage sludges. Plants stunt their growth, yellow and usually die when zinc is overly abundant. High zinc levels can interrupt the metabolic activity in soils, as zinc negatively harms microorganisms and earthworms, slowing down breakdown of organic matter that provides basic nutrition to plant roots. Some plants are naturally more tolerant of high zinc levels in soils, such as grasses, while broad-leaf weeds may be more sensitive. Vegetable crops tend to be much more sensitive to zinc levels, according to the University of Michigan.