Wastewater reclamation and reuse represent a feasible solution to meet the growing demand for safe water. An environmentally sustainable technology such as phytoremediation is targeted for the reclamation of polluted waters. To this end, the capability of different plant species to tolerate and accumulate pollutants has to be investigated. In this work, eucalypt plants were studied by analysing biometric, physiological, and biochemical parameters related to cadmium (Cd) tolerance and accumulation in two clones (“Velino ex 7” and “Viglio ex 358”) of
Anthropogenic activities have led to the global degradation of the quality of surface and groundwater, thus representing a severe threat to the environment and human health. In this regard, cadmium (Cd) pollution is of special concern due to the high toxicity of this metal to biota, even at low concentrations, and its high solubility in water. Cadmium has no biological function in plant growth but it is readily taken up and accumulated in the edible parts of crops through the metabolic pathways of essential nutrient elements, especially Zn and Fe, thus entering the human food chain, causing a wide variety of acute and chronic toxic effects (
Due to the world population increase, the demand for safe water represents a global challenge. Thus, appropriate management of the water resources is required. In this regard, wastewater reclamation and reuse has become an attractive solution to the problem of the water shortage related to crop irrigation. In many countries irrigation with raw wastewater is a commonly utilised agricultural practice, possibly causing the accumulation of metals in the soil and their transfer into food plants (
Most studies on heavy metal tolerance and accumulation by forest plants have been focused on poplars and willows due to their deep and extensive root systems, fast growth, high evapo-transpiration rates, easy management, and low impact on trophic chains (
The
The aim of this study was to investigate the metal tolerance, accumulation, and organ distribution in two hybrid clones of
One-year-old rooted cuttings of two eucalypt hybrid clones
Biomass data were utilised for the calculation of different biometric parameters. The tolerance index (T
The calculation of the organ mass ratio was performed as the ratio of the leaf (LMR), stem (SMR) and root (RMR) biomass to the total plant biomass.
Two cm2 of the last fully expanded leaf, sampled at the end of the experiment, were extracted in 80% chilled acetone in the dark. After centrifugation at 10.000×
At the end of the treatment, the chlorophyll a fluorescence transient (OJIP transients) was measured on the last fully expanded leaves of both eucalypt clones, using a Plant Efficiency Analyser (PEA, Hansatech Instruments Ltd., King’s Lynn, UK). The measurements were performed on leaves that were previously adapted to the dark for 60 minutes for the complete oxidation of the photosynthetic electron transport system, and the fluorescence intensity was measured for 1 s after the application of a saturating light pulse of 3000 μmol m-2 s-1. The JIP-test was employed to analyse OJIP transient and bioenergetics parameters: size and number of active reaction centre of photosynthetic apparatus (Fv/F0), efficiency of water splitting complex (F0/Fv), quantum yield of primary photochemistry (Fv/Fm or ΦP0), performance index of PS II (PIABS) were determined as described by
Cadmium concentration was measured using an atomic absorption spectrophotometer (Perkin Elmer, Norwalk, CT, USA) on digested samples. Dried material was milled to a fine powder (Tecator Cemotec 1090 Sample Mill - Tecator, Hoganas, Sweden), weighed and mineralised as reported elsewhere (
The metal uptake ratio describes the capability of the plant to extract and accumulate Cd and it was calculated as the ratio of the Cd content in the whole plant to the Cd content of the corresponding growth solution (
The metal translocation index describes the ability of the plant to translocate the metal and it was measured as the ratio of the Cd content of the aerial parts (leaves and stem) to the Cd content of the corresponding roots (
The metal content in plant parts was calculated by multiplying the dry weight by the metal concentration.
The metal phytoextraction efficiency (mg g-1) was calculated according to
The data reported refer to a single typical experiment with five replicates. Normally distributed data were processed with a one or two-way analysis of variance (ANOVA), depending on the number of the factors of variability, using the software SPSS® (Chicago, IL, USA). Statistical significance of the differences between means was assessed by Duncan’s test (P ≤ 0.05), unless otherwise stated.
Metal tolerance is a basic factor affecting the efficiency of the phytoremediation processes, and its evaluation represents a step of the utmost importance in plant screening for phytoremediation purposes (
The variation of the biomass allocation among organs is considered a suitable parameter which contributes to the efficient selection of plants to be used in phytoremediation applications. In this work, control plants showed a similar trend in biomass partitioning (
When Cd is taken up by the roots, it may be translocated to the aerial parts of the plant
Eucalypt clones showed similar values for chlorophyll
Metal content is an important parameter to investigate in candidate plants for phytoremediation, as the ability to absorb and accumulate metals in plant tissue is a basic trait for phytoextraction purposes. This trait is also considered a good indicator of the efficient detoxification and tolerance mechanisms (
To better highlight the ability of the two clones to extract Cd from the solution and accumulate it in plant tissues, the metal uptake ratio and the phytoextraction efficiency were evaluated (
Among the physiological processes associated with heavy metal tolerance in plants, the restriction of metal transport to the aerial parts has been highlighted in non hyperaccumulating plants (
In this work, an investigation into the biometric, physiological, and biochemical traits associated with the ability of eucalypt plants for the phytoremediation of Cd-polluted waters was performed. The results obtained highlighted the notable ability of this plant species to tolerate and phytoextract the metal from the nutrient solution. Consistent with the little evidence present in the literature, eucalypt plants showed prevalent Cd accumulation in the root system with a low translocation to aerial organs. This finding has remarkable implications for phytoremediation, as the limitation of metal transport to leaves allows plants to better cope with metal exposure and to avoid a recycling of the metal from the rhizosphere to the soil top layers by leaf shedding. For the reclamation of metal polluted waters, the uppermost Cd accumulation in the roots is not to be considered a drawback, as in the water decontamination bio-systems the below-ground plant biomass can be harvested at the end of the decontamination cycle, removing the metal accumulated by the roots. Given the notable tolerance of eucalypt plants to submersion and their adaptability to extremely wide pedoclimatic conditions, the results obtained in this work suggest that this plant species could be proposed for the reclamation of Cd-polluted waters.
Authors wish to thank Mr. Ermenegildo Magnani for his valuable technical assistance in metal content analysis.
Tolerance index (T
Clone | Roots | Stem | Leaves | Total plant |
---|---|---|---|---|
Velino | 0.68 ± 0.08 a | 0.72 ± 0.11 | 0.89 ± 0.14 | 0.70 ± 0.11 a |
Viglio | 0.44 ± 0.14 b | 0.59 ± 0.11 | 0.72 ± 0.16 | 0.47 ± 0.10 b |
Organ mass ratio (g g-1 DW) in plants of two eucalypt hybrid clones treated with 0 (C) and 50 µM CdSO4 (Cd) in hydroponics for three weeks. Data are mean values ± standard error (n=5). Different letters in the same column indicates significantly different values after Duncan test. (***):
Clone | Treatment | Root:mass | Stem:mass | Leaf:mass |
---|---|---|---|---|
Velino | C | 0.42 ± 0.01 | 0.27 ± 0.01 | 0.31 ± 0.01 |
Cd | 0.29 ± 0.02 | 0.31 ± 0.01 | 0.38 ± 0.03 | |
Viglio | C | 0.41 ± 0.02 | 0.26 ± 0.004 | 0.32 ± 0.01 |
Cd | 0.27 ± 0.21 | 0.34 ± 0.01 | 0.38 ± 0.41 | |
Clone | ns | ns | ns | |
Treatment | *** | *** | *** | |
Clone × Treatment | ns | ns | ns |
Leaf biometric parameters in plants of two eucalypt hybrid clones treated with 0 (C) and 50 µM CdSO4 (Cd) in hydroponics for three weeks. Data are mean values ± standard error (n=5). Different letters in the same column indicates significantly different values after Duncan test. (*):
Clone | Treatment | Leaf Area(cm2) | Specific Leaf Weight (SLW, g cm-2) | Specific Leaf Area(SLA, cm2 g-1) |
---|---|---|---|---|
Velino | C | 148.6 ± 17.8 | 0.0284 ± 0.0026 | 37.4 ± 1.6 ab |
Cd | 131.5 ± 9.4 | 0.0269 ± 0.0031 | 35.3 ± 1.1 b | |
Viglio | C | 175.2 ± 17.1 | 0.0285 ± 0.0042 | 35.4 ± 1.7 b |
Cd | 161.4 ± 16.6 | 0.0235 ± 0.0052 | 43.6 ± 3.5 a | |
Clone | * | ns | ns | |
Treatment | *** | * | ns | |
Clone × Treatment | ns | ns | * |
Chlorophyll content and chlorophyll ratio evaluated in plants of two eucalypt hybrid clones treated with 0 (C) and 50 µM CdSO4 (Cd) in hydroponics for three weeks. Data are mean values ± standard error (n=5). Different letters in columns indicate significantly different values after Duncan’s test. (**):
Clone | Treatment | Chl |
Chl |
Tot Chl(µg cm-2) | Chl |
---|---|---|---|---|---|
Velino | C | 21.08 ± 0.53 a | 6.57 ± 0.16 a | 27.65 ± 0.60 a | 3.2070 ± 0.0005 a |
Cd | 14.54 ± 0.60 b | 4.55 ± 0.18 b | 19.09 ± 0.79 b | 3.1890 ± 0.0053 b | |
Viglio | C | 22.79 ± 0.89 a | 7.11 ± 0.28 a | 29.91 ± 1.17 a | 3.2034 ± 0.0016 ab |
Cd | 11.99 ± 0.71 c | 3.79 ± 0.21 c | 15.79 ± 0.92 c | 3.1533 ± 0.0102 c | |
Clone | ns | ns | ns | *** | |
Treatment | *** | *** | *** | *** | |
Clone × Treatment | *** | *** | *** | ** |
Leaf chlorophyll fluorescence parameters, size and number of active reaction centre of photosynthetic apparatus (Fv/F0), efficiency of water splitting complex (F0/Fv), quantum yield of primary photochemistry (Fv/Fm, ΦP0), performance index of PS II (PIABS) evaluated in control (C) and in 50 µM CdSO4 (Cd) treated cuttings of two eucalypt hybrid clones in hydroponics for three weeks. Data are mean values ± standard error (n=5). Different letters in columns indicate significantly different values after Duncan’s test. (*):
Clone | Treatment | Fv/F0 | F0/Fv | Fv/Fm (ΦP0) | PIABS |
---|---|---|---|---|---|
Velino | C | 3.86 ± 0.08 | 0.259 ± 0.005 | 0.793 ± 0.003 | 13.98 ± 0.72 a |
Cd | 2.61 ± 0.09 | 0.392 ± 0.015 | 0.719 ± 0.007 | 4.97 ± 0.39 b | |
Viglio | C | 3.63 ± 0.08 | 0.277 ± 0.006 | 0.783 ± 0.003 | 13.16 ± 0.62 a |
Cd | 2.35 ± 0.10 | 0.430 ± 0.020 | 0.701 ± 0.010 | 2.22 ± 0.21 c | |
Clone | * | ns | * | ** | |
Treatment | *** | *** | *** | *** | |
Clone x Treatment | ns | ns | ns | * |
Root, stem, leaf and total cadmium content (mg plant-1), uptake ratio (mg mg-1), metal translocation index and phytoextraction efficiency (mg g-1) in plants of eucalypt hybrid clones treated in hydroponics for three weeks with 50 µM CdSO4. Data are mean values ± standard error (n=5). Different letters in the same column indicate significantly different values after
Clone | Cadmium content | Uptakeratio | Metal Translocation Index | Phytoextractionefficiency | |||
---|---|---|---|---|---|---|---|
Root | Stem | Leaves | Total plant | ||||
Velino | 36.7 ± 3.3 a | 0.21 ± 0.01 a | 0.011 ± 0.002 | 38.5 ± 3.43 a | 0.21 ± 0.01 a | 0.049 ± 0.005 | 0.63 ± 0.03 a |
Viglio | 21.9 ± 2.3 b | 0.12 ± 0.01 b | 0.006 ± 0.001 | 23.3 ± 2.51 b | 0.12 ± 0.01 b | 0.064 ± 0.021 | 0.36 ± 0.06 b |