B f sr I Cs v GO

from \ salt water \ to fresh water systems

- essential for plants and animals

- essential for plants only

# * essential for animals only

0 - no essential function known at present

# - blanks for unpositioned elements

# - essential for certain plants or animals

- essential for plants and animals

- essential for plants only

# * essential for animals only

0 - no essential function known at present

# - blanks for unpositioned elements

# - essential for certain plants or animals

from lower to higher aggregation of moiecules (mac romolecu les)

The biological system of the elements (BSE) compiled from data on correlation analysis, the physiological functions of the individual elements in living organisms, evolutionary development from the inorganic environment, and the forms of the elements taken up by plants as neutral molecules or charged ions. The elements H and Na perform various functions in biological systems, so they are not conclusively fixed in the BSE. The ringed elements can only be summarized as groups of elements with similar physiological function at present, since there is a lack of correlation data on them or these data are currently too imprecise. [From Markert B (1994) The biological system of the elements (BSE) for terrestrial plants (glycophytes). Sci Total Environ 155:221-228].

Quantitatively, the uptake of substances is adequately characterized by the intensity and scale of the uptake up to a particular point in time. For a defined nutrient, the uptake by the plant is dependent on the amount of the nutrient in the medium taken up and its availability. As a rule, the plant has no positive influence on the supply, but it does have an effect on the material and spatial availability of the nutrients. For example, from a material aspect, the nutrient availability can be changed by modifying the pH of the soil solution (elimination of H3O+ or HCO3-ions by the root), by the liberation of organic acids with chelating-like activity from the root, or via the participation of microorganisms (mycorrhiza), as well as by the effect of the release of H3O+ and O2 at the root surface on the redox potential in the soil. The most readily available elements are present in the soil solution as ions or as soluble soil complexes. The least readily available are tightly bound to the soil structure, for example as a secondary component of the crystal structure of primary minerals. The most important sources of elements between these two extremes are small particles that are loaded with metals and have large surface areas, such as clay, sludge, and organic material. Taken together, all of this can be termed an

"exchange complex". Ion exchange, such as that between calcium and magnesium, potassium, or hydrogen, can occur at the surface.

Thus, the intensity and the range of the uptake both influence the actual amount of a specific element in the plant. Depending on the type of plant being studied, the element species, and the specific location, one can differentiate between roughly three kinds of uptake. In the ideal situation, there is a direct proportionality between the amount of nutrients available and the amount taken up by the plant. In this case, the specific elemental content of the plant reflects the concentration ratios in the nutrient substrate. Thus, the chemical composition of the plant has an indicative character. This association, which has been observed in a series of plants and for a wide variety of elements, both in experiments and in the field, is being taken into account more and more in practical applications, such as when prospecting for ore, or when (usually low-level) plants are used for biomonitoring. Because of unfavourable locations, many plants have developed the ability to enrich themselves with high concentrations of individual elements, often regardless whether these elements are physiologically useful or not. These plants are called accumulators. For example, most Ericaceae have high concentrations of manganese, and beeches have high levels of zinc. This accumulative behaviour, which may have genetically predetermined origins rather than ones determined by location, makes it possible to chemically fingerprint a very wide variety of plant types. The rejection or a reduced uptake of individual elements occurs less frequently than the accumulation of elements, but rejection behaviour has also been demonstrated for numerous plant species. The reduction in concentration of an element in an organism can be the result of complete or partial exclusion.

To advance the abovementioned scientific fields, a more integrative approach to student education appears to be necessary. International exchanges and dialogue about complex problems related to the toxicological effects of heavy metals from the atmosphere and soils on organisms are of tremendous importance. The financial resources needed to achieve these goals must be contributed by various national and international governments.

International Graduate School Prof. Dr. Bernd Markert

Zittau, Germany April 2009

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