Zinc [Zn, 30]
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weather, and also to bacterial and fungal diseases, due to its positive impact on levels
of proteins, chlorophyll, and abscisic acid. (Zengin vide Kabata-Pendias 2011).
The bioavailability of Zn is a function of several plants and soils properties. The
most important soil factors limiting its uptake are (1) low soil Zn content, (2) calcareous soils and pH > 7, (3) low OM level, (4) microbial inactivation of Zn, and
(5) antagonistic effects of other chemical elements. Phytotoxic threshold levels of
Zn in soils extracted with 1 M HCl was established in the experiment with spring
wheat at 65 mg/kg for acidic media (pH < 4.6) and at 144 mg/kg for alkaline media
(pH > 6.6) (Stanisławska-Głupiak and Korzeniowska 2014).
There are several observed and reported interactions of Zn and other elements, of
which the most common and important are as follows:
r Zn–P interaction is relatively common, especially after phosphate and lime
applications. Addition of P decreases Zn concentration in soil solution, and
thus its availability to plants, and may induce its deficiency. Sometimes,
there is also an observed impact of Zn on P uptake by plants. The balanced
P and Zn amounts in plants nutrition seem to be essential for the proper
activity of Rhizobium and N fixation.
r Zn–N interaction is mainly a secondary effect, resulting from increased
biomass under heavy N treatment. The elevated content of proteins and
amino acids in roots may disturb Zn transport to plant tops.
r Zn–Ca and Zn–Mg interactions vary for a given plant and media and
depend on several other factors. Therefore, there are both observed antagonistic and synergistic effects. In general, the elevated amounts of Ca and
Mg decrease Zn phytoavailability.
r Zn–Fe antagonism is widely observed. There are two possible mechanisms
of this interaction: (1) the competition between Zn 2+ and Fe 2+ in uptake
processes and (2) the interference in chelation processes. Iron decreases Zn
absorption and toxicity.
r Zn–Cd interaction may be both antagonistic and synergistic in uptake and
transport processes. However, most often there are observed synergistic
effects in field conditions, especially at low pH values. Some plants with
high Zn content reveal a tolerance to increased Cd levels.
r Zn–As interaction is observed in plants with high content of As, whose
toxic effects decrease at elevated Zn amounts.
Zinc contents of plants vary considerably, reflecting impact on both ecosystems and plant
genotypes. Nevertheless, its concentrations in some plants, mainly cereal grains and pasture herbage, do not differ widely. The mean Zn contents (rounded) of cereal grains from
various EU countries are (in mg/kg) as follows: wheat, 25; barley, 26; and oats, 33. The
background Zn contents in fodder plants, throughout the world, are also relatively similar
and vary in grasses from 12 to 47 mg/kg and in clovers from 24 to 45 mg/kg.
Pollution of both air and soils greatly influences the Zn content of plants. Plants
cultivated in nonferric metal-mining region contain this metal up to 530 and 710 mg/kg,
in lettuce leaves and onion bulbs, respectively. Zinc concentration in plants from areas
of various metal industries was the highest in lettuce leaves, 393  mg/kg, and carrot