Physiological and growth responses to cadmium exposure in hydroponic culture of Salicaceae to select clones with phytoremediation ability
Author(s)
Fabrizio, Pietrini
Date Issued
April 23, 2008
Type
Doctoral Thesis
Abstract
The presence of contaminated sites in ever increasing numbers brings several management problems and
often leads to a waste of important resources, such as soils and water which cannot be utilised. Remediation
with conventional technologies is sometimes unfeasible due to economic reasons or for the opposition of the
public opinion, but it is often the only available alternative. Since many years, biological techniques for
remediation, bioremediation and phytoremediation, have been studied; they can give acceptable results with
a lower environmental impact, even if with longer time periods. In particular, the use of higher plants in
decontamination has been limited by legislation constraints, and also for lack of plant species which can be
really effective towards specific contaminants. The main objective of this thesis was to enhance the
potentials to remediate the environmental contamination through biological systems. It is considered that
poplars and willows can contribute to this objective for some reasons:
1) poplars and willows have a fast rate of growth, high biomass productivity, high transpiration rate and
grow easily from cuttings; 2) there are experimental evidences of a wide genetic variability between and
within species concerning the ability to absorb and immobilize metals inside the plants and their allocation to
the various plant organs; 3) exists a wide germplasm availability of both genera that include interspecific
hybrids, partially of exotic provenance, and species of the national flora. In this context, the specific
objective was to evaluate phytoremediation capability of some poplar and willow clones for cadmium
tolerance, accumulation and translocation by a hydroponic screening. Rooted cuttings were exposed for three
weeks to 50 μM cadmium sulphate in a growth chamber and physiological parameters and cadmium content
distribution among plant parts were evaluated. The results allowed to select some clones that were better able
to survive, grow and accumulate cadmium than others. In fact these clones adapted to cadmium presence, by
means of growth and eco-physiological changes, such as maintenance of photosynthesis and transpiration,
cadmium allocation in roots or original cuttings, developing of protective mechanisms and changing the
allocation pattern of biomass. Poplar clones, with similar characteristics of accumulation, distribution and
tolerance to cadmium, were classified by means of hierarchical cluster analysis. Moreover, tolerance index
(Ti), bio-concentration factor (BCF) and translocation factor (Tf) were analysed to compare the behaviour of
poplar and willow clones with regard to cadmium tolerance, accumulation and translocation to aerial parts.
On average, poplar clones showed a two times higher capability to remove metal from the solution respect to
willow, expressed as total BCF. On the other hand willow clones exhibited a more than double ability to
accumulate metal in the aerial parts respect poplar, expressed as Tf. Comparison between the two species for
that regards cadmium tolerance was highlighted by the analysis of Ti. On the basis of the dry biomass of
total plant, on average of all clones analysed, Ti revealed that willows tolerate cadmium much more than
poplars. Finally, the effects of cadmium on poplar and willow clones with different translocation capacity to
leaves were examined by imaging chlorophyll fluorescence analysis to characterise the damage produced by
metal at leaf level. This technique has been shown to be capable of revealing spatial and temporal changes
during plants stress development as well as environmental effects on several aspects of whole plant
physiology. For this study poplar and willow clones with an increasing content of cadmium in leaves were
used. The results indicated that willow clone was more tolerant at leaf level than other poplar clones, as
maintained a high photosynthetic activity. Nevertheless, while poplar clones showed a low cadmium content
willow clone exhibited the highest one. Such a discrepancy could be ascribed to a different mobility of heavy
metals inside and between cells in the tested clones. Probably, willow bound cadmium in the veins and in
necrotic areas on leaf surface without to damage the rest of the leaf blade, while poplars showed a wide
diffusion of the damage.
Additional information
Dottorato di ricerca in Ecologia forestale
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