Page 230 - Plant-Based Remediation Processes

222 M. Griga and M. Bjelkova ´

(probably inflorescence) > roots > stems > leaves > seeds. Surprisingly high HMs
content in flowers cannot be compared to other data as this is the only report on
HMs content in hemp flowers (inflorescence) in literature. Citterio et al. (2005)
studied HMs (Cd, Ni, Cr(VI)) accumulation changes caused by artificial
mycorrhization (fungus Glomus mosseae) of hemp plants. Plants with artificially
increased Cd, Ni and Cr concentrations accumulated most metal in the roots.
However, in such soil, mycorrhization significantly enhanced the translocation of
all three metal elements from root to shoot.
Similarly as in flax, it is difficult to make a generalisation for organ distribution
of HMs within hemp plant, namely due to difficult comparability of particular
reports (various methodology, namely hydroponics x pot experiment x field trial;
various starting concentrations of HMs in soil/solution; various genetic materials
used in experiments; various treatments to affect bioavailability of HMs, etc.). As
related to hemp, it is also problematic to make conclusions from greenhouse pot
experiments if the mature hemp plant normally reaches 2–4 m height in the field
conditions. In such case, the field experiment represents the most objective
approach. Despite of some contradicting data (Table 11.4) we may conclude the
hemp plant tolerates and accumulates a spectrum of toxic metals without dramatic
changes of growth and development when grown on medium concentrations of
particular HMs. However, substantially increased contamination (e.g. 72 mg Cd
kg 1 soil; Linger et al. 2005) results in irreversible damage of meristems, inhibition
of photosynthesis and thus in growth retardation or plant death. In such comparison,
the flax/linseed seems to be more tolerant (Bjelkova ´ et al. 2011a, b).

11.5.3 Agrotechnological Treatments to Improve Heavy Metal
Phytoextraction

The series of studies have been carried out during last 25 years in Germany, Poland,
USA, Canada and Australia, which evaluated an effect of soil and climatic factors
on accumulation of heavy metals (mainly Cd) by flax plants. Some of the studies
concentrated on simple collection of data from various locations and various soil
types of certain country (sample analysis from farms; Germany, Australia) without
active treatments of agrotechnology (Klein and Weigert 1987; Marquard et al.
1990; Li et al. 1997; Hocking and McLaughlin 2000), others evaluated an effect
of P, N, Zn fertilisation, pH changes or artificial increase of total Cd or Zn in the soil
on the uptake and accumulation of Cd or Zn in the seed and other plant parts.
Experiments were realised both in the field conditions and in the greenhouse or
growth chamber with collected defined soil samples. Extensive investigation (490
seed samples) of seed contamination of linseed by heavy metals in the whole region
of Germany (Klein and Weigert 1987) brought first information on the seed content
of essential as well as toxic metal elements (Table 11.5). Only several further
studies followed accumulation of broader spectrum of metal elements in flax