Transcript PHOTOSYNTHETIC AND GROWTH RESPONSES OF Populus …

PHOTOSYNTHETIC AND GROWTH RESPONSES OF Populus CLONES I-214 AND ERIDANO TO ELEVATED Zn CONCENTRATIONS
JORDI FERNÀNDEZ1, MASSIMO ZACCHINI2 and ISABEL FLECK1
1Departament de Biologia Vegetal. Unitat Fisiologia Vegetal. Facultat Biologia. Universitat de Barcelona. Diagonal,645; 08028 Barcelona. E-mail: [email protected]
2Istituto di Biologia Agroambientale e Forestale-CNR. 00015 Monterotondo Scalo (Roma), Italy.
INTRODUCTION
The capability of plants to absorb and concentrate metals in their organs is a basic characteristic to be utilized for the
remediation of metal polluted substrates. Poplars are plant candidates for phytoremediation purposes because of its variability
and adaptability towards environmental constraints, extended root system and a low impact on trophic chains. Poplar clones, I214 (Populus x canadiensis euramericana Mönch.) and Eridano (P. deltoides x maximowiczii) were exposed to two different toxic
levels of Zn in hydroponics to evaluate their capability to tolerate and concentrate the metal in plant parts, the effect on its
development and photosynthetic activity and their efficiency for phytoremediation purposes.
MATERIAL AND METHODS
Rooted cuttings of poplar clones Eridano (Photos1-3) and I-214 (Photos 4-6) were treated for three weeks in hydroponic culture
(Moore nutritional solution) with 0 (control), 1mM and 5mM ZnCl2. Thereafter, leaf gas-exchange on attached leaves was
determined with a Li-Cor 6400 system. Plants were then separated into young leaves, old leaves (already present at the beginning
of Zn addition), stem, woody cuttings and roots for biomass and morphological characteristics determination. Zn concentration after
digestion in concentrated HNO3-HClO4 (2:1) was determined by inductively coupled plasma mass spectrometry (ICP-MS
PerkinElmer, model Elan-6000).
Photo1
Photo 2
Table1. Biomass characteristics in clones Eridano and
I-214 submitted to 0, 1 or 5mM ZnCl2. Significant
differences (P < 0.05) are indicated by different letters:
clones (a,b) and Zn treatments (A,B).
Photo 4
Photo 3
Photos 1-3. Clone Eridano leaves in Control (1), 1mM ZnCl2 (2) and 5mM
ZnCl2 (3) treatments.
•Zinc concentration in organs (Fig.2)
In both clones, an increase of [Zn] in the growth
medium resulted in a higher [Zn] in plant parts. No
differences between clones were observed at 1mM ;at
5mM Eridano showed higher [Zn] in shoot, root and
cuttings. At this concentration, a notable higher Zn
levels in young leaves of both clones in comparison to
old leaves occurred.
•Gas-exchange parameters (Table 2)
Net photosynthesis (A), stomatal conductance (gs)
and transpiration rate (E) decreased at high levels of
Zn (5mM) in old and young leaves of both clones
whereas 1mM gas-exchange was only affected in I214.
Photo 5
Photo 6
Photos 4-6. Clone I-214 leaves in Control (4), 1mM ZnCl2 (5) and 5mM ZnCl2 (6) treatment
(a)
(b) (b)
RESULTS AND DISCUSSION
•Plant’s biomass characteristics (Table1)
The effect of increasing
[Zn] was especially
remarkable at 5mM [Zn] on clone I-214 total biomass
with a decline in old and young leaves, cuttings, stem
and root biomass. The number of young leaves, stem
length and stem diameter was also lower.
•Leaf Morphological Parameters (Fig.1a and 1b)
Leaf area (LA) was highest in Eridano old and young
leaves in all treatments. In I-214 no effect of Zn
treatment was observed in old leaves, whereas young
leaves with 1 and 5 mM Zn treatment showed a similar
decline. Leaf mass per area, LMA, (Md/LA), and its
components [(Md/Mf)·100], and (Mf/LA) as indicators
of leaf density (D) and leaf thickness (T) were similar
in old leaves of both clones in control and 1mM
treatment whereas 5mM affected I-214 that showed
diminished LMA and T and increased D with respect to
Eridano. Young leaves showed differences between
clones at 5mM with lower values of LMA and T and
higher values of D in I-214 indicative of a lower
photosynthetic capacity and water availability.
Table 2. Net photosynthesis (A), stomatal conductance (gs)
and transpiration rate (E) in old and young leaves of
Eridano and I-214 clones submitted to 0, 1 and 5mM ZnCl2.
Significant differences (P < 0.05) are indicated by different
letters: clones (a,b in the center); old or young leaves
between Zn treatments (A,B), old and young leaves in each
treatment (a,b at the sides).
CONCLUSIONS
• Eridano showed a
greater capability to
accumulate this element especially in roots
and lower alterations in the development of
plants biomass and structural parameters,
photosynthetic activity and water relations.
Figure 2. Zinc concentrations in organs of clones Eridano
and I-214 submitted to 0, 1 or 5mM ZnCl2. Significant
differences (P < 0.05) are indicated by different letters:
clones (a,b) and Zn treatment (A,B).
Figure 1. Leaf area (LA), Leaf Mass per Area (LMA), Leaf densitity (D) and Leaf thickness (T) in
old leaves (Fig.1a) and young leaves (Fig.1b) of Eridano and I-214 clones submitted to 0, 1 and
5mM ZnCl2. Significant differences (P < 0.05) are indicated by different letters: clones (a,b) and
Zn treatments (A,B).
• The effect of increasing [Zn] was observed
in the physiological responses of I-214 and
Eridano clones; [Zn] 1mM was tolerated by
Eridano whereas [Zn] 5mM originated serious
problems in both clones.