10
Phytotechnology with Biomass Production
(Baker, 1981; Mamirova et al., 2020). Malayeri et al. (2008) and Zgorelec (2009)
grouped plant species according to their ECs uptake capacities related to
trace elements and sensitivity to trace element contamination as follows:
high-accumulator plants EC 1–10
medium-accumulator plants EC 0.1–1
low-accumulator plants EC 0.01–0.1
nonaccumulator plants EC < 0.01
The sensitivity or tolerance of plants to excess trace elements depends on plant
species and their genotypes. Even among crops, sensitivity varies widely
(Adriano, 2001). Excluders are tolerant to high-trace elements concentrations and
their tolerance is achieved by preventing the absorption and translocation of
toxic elements to aboveground biomass. However, the observed concentrations
in the root are lower than those in the soil. These species have low potential for
metal extraction, and EC value is less than one (Lasat, 1999). They are insensitive to trace elements over a wide range of concentrations, and a common
example is various grass species. Indicators are plant species sensitive to trace
elements and consequently certain symptoms can be manifested. Such plants
are not tolerant to high concentrations of trace elements, and examples are grain
and cereal crops (Adriano, 2001). Accumulators are plants which accumulate
trace elements in various concentrations, however, in concentrations which are
still lower than in case of hyperaccumulators. Hyperaccumulation is a specific
characteristic inherent in certain species. The majority of hyperaccumulators
are endemic plants which grow in soils rich in trace elements and behave like
strict metallophytes (Baker & Brooks, 1989), where certain facultative metallophytes can survive in soils poor in the trace elements (Rascio & Navari-Izzo,
2011). These plants have developed special mechanisms for element uptake
and tolerance to high concentrations. The mechanisms are genetically conditioned because the plant tissues do not manifest toxicity symptoms typical in
plants due to high element concentrations. For successful hyperaccumulation
the concentrations of the trace elements in the above-ground biomass have to
be extremely higher compared to their content in the soil (Pulford & Watson,
2003). The negative aspect of hyperaccumulators is low biomass yield.
2.3 Phytostabilization of Arable Land
Contaminated with Trace Elements
Phytostabilization uses plants to reduce contaminated soil material movement
via water or wind. The approach is commonly used in combination with soil
amendments to reduce contaminant bioavailability and to assist plant growth.