PHOTOSYNTHETIC AND GROWTH RESPONSES OF Populus CLONES I-214 AND ERIDANO TO ELEVATED Zn CONCENTRATIONS JORDI FERNÀNDEZ 1, MASSIMO ZACCHINI 2 and ISABEL FLECK 1 1Departament de Biologia Vegetal. Unitat Fisiologia Vegetal. Facultat Biologia. Universitat de Barcelona. Diagonal,645; Barcelona. 2Istituto di Biologia Agroambientale e Forestale-CNR 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, I- 214 (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. 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 I 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 HNO 3 -HClO 4 (2:1) was determined by inductively coupled plasma mass spectrometry (ICP-MS PerkinElmer, model Elan-6000). 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. 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. Photos 1-3. Clone Eridano leaves in Control (1), 1mM ZnCl 2 (2) and 5mM ZnCl 2 (3) treatments. Table1. Biomass characteristics in clones Eridano and I-214 submitted to 0, 1 or 5mM ZnCl 2. Significant differences (P < 0.05) are indicated by different letters: clones (a,b) and Zn treatments (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 ZnCl 2. Significant differences (P < 0.05) are indicated by different letters: clones (a,b) and Zn treatments (A,B). Figure 2. Zinc concentrations in organs of clones Eridano and I-214 submitted to 0, 1 or 5mM ZnCl 2. Significant differences (P < 0.05) are indicated by different letters: clones (a,b) and Zn treatment (A,B). 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 ZnCl 2. 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). 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. (b) Photo1Photo 2Photo 3 Photo 4 Photo 5Photo 6 Photos 4-6. Clone I-214 leaves in Control (4), 1mM ZnCl 2 (5) and 5mM ZnCl 2 (6) treatment (a) (b)