alba L.

Source: www.actaplantarum.com Source: www.arbolesyarbustos.com photo: S. Radivo Origin and diffusion

Origin: northern Africa, southern , west and central Distribution: northern Africa, southern Europe, west and central Asia and North America Invasive potential: medium

Source:www.actaplantarum.com Source: www.actaplantarum.com photo: F. Cerrai photo: S. Radivo

Introduction

P. alba is a fast-growing , with a straight and thin trunk, it varies in form from tall and straight to broad-crowned, crooked and multi-stemmed. The crown is spindle-shaped and elongate; the vibrate in the slightest breeze and produce a typical sparkling effect, that is accompanied with a slight rustling. The appearance of this tree varies considerably according to the season, changing the surrounding landscape: in autumn the crown takes on a golden-yellow color, in winter the thin silhouette of the trunk and of the bare brunches stands out on the sky, while in summer, after the appearance of new leaves, the poplar releases abundant cottony-tufted seeds which fly into the air, creating a veritable “snowstorm” of cotton and whitening the nearby soil. The bark is metallic grey to chalky-white on young , later developing numerous lenticels which enlarge and develop into shallow dark splits and ridges. White poplar is distinguished from other poplars by its three-lobed leaves that are bright silver-white on their undersides.

It is a pioneer species, well adapted to moist environments, such as flood plains and riparian areas; however, it grows rapidly in a variety of challenging conditions, tolerating a wide range of soils or disturbed habitats. Fast-growing poplars, having high productivity, high genetic diversity and being easily clonable, have a good potential as a short-rotation coppice crop (SRC) grown for biomass energy. Because of its distinctive columnar form, the well-known ‘Bolleana’ has been a popular tree for ornamental and line plantings through the word

Common names: Withe poplar (English); Pioppo bianco (Italian)

Fam.

Description Life-form and periodicity: perennial tree, deciduous Height: 5-40 m Crown: oval open crown, with irregular outline Roots habit: extensive root system, homogenously exploring large soil volumes. Average root spread largely exceeds crown radius. Extreme ability to root.

Probable rooting depth range for mature trees:

. in soils with wet lower horizons: < 3,5 m;

. in other types of soil: < 2 m.

root/shoot ratio: 1.1

Culm/Stem/Trunk: generally it has a single straight trunk, but can also grow as a multi-trunked tree. The bark is metallic grey to chalky-white on young trees, later developing numerous lenticels which enlarge and develop into shallow dark splits and ridges. : shape varies from the ovoid to deltoid, coarsely toothed preformed leaves to tree- to five- lobed, maple-like neoformed leaves. Dark green above, with covering thick white felt below.

Rate of transpiration: very high

Reproductive structure: dioecious, with tiny reddish male and greenish female flowers appearing in separate catkins on separate male and female trees before the foliage emerges. Flowering catkins are not showy. Propagative structure: Flowers in female catkins give way to small dehiscent capsules that typically ripen and split open, distributing abundant cottony-tufted seeds.

Development Sexual propagation: it produces abundant seed, dispersed by the wind. Asexual propagation: it suckers vigorously from shallow roots, forming large colonies. Hardwood cuttings can be used for propagation.

Growth rate: fast

Habitat characteristics Light and water requirement: full sun, it grows better in wet soil. Soil requirements: it tolerates almost any soil Tolerance/sensitivity: tolerant of drought, wind, salinity and high temperatures, it suffer from winter dieback and frost injury.

Phytotechnologies applications Because of its rapid growth, its abundant transpiration activity and its extensive and dense root system, poplar is considered as an interesting candidate for phytoremediation activities. Poplar plantations have been used to remediate different types of contamination in soil, in water and in atmosphere; the removal efficiency and the contaminant tolerance greatly depend from the poplar genotype and vary significantly among the different hybrids. The ease with which it is possible to create new hybrids and to propagate them by cuttings allows the selection of the more suitable clone for each different case of pollution (Di Lonardo et al., 2011). The rhizosphere of poplar hosts many mycorrhizal fungi that will improve the phytoremediation efficiency. Poplars are used to extract heavy metals from soil or water (in hydroponics or through irrigation of the ground); in this case the mechanism involved in phytoremediation is the hyperaccumulation of the contaminants into the tissues. An important issue to be addressed in this context is the fate of the contaminated biomass resulting from the phytoremediation process (Dos Utmazian Santos et al., 2007; Unterbrunner et al., 2007; Zacchini et al., 2009, Marmiroli et al., 2011). Concerning particularly stable organic contaminants, in addition to the process of absorption and/or degradation within the plant tissues, the rhizosphere of poplar helps to create an ideal environment for the proliferation of microorganisms capable of degrading substances such as tri- and tetra-cloroesano (Newman et al., 1997), pharmaceutical compounds (Iori et al., 2012), lindane and polychlorinated biphenyls (Bianconi et al., 2011; Bell et al., 2002, Passatore et al., 2014). This species plays an essential role in riparian ecosystems, thanks to its proven ability to absorb and remove the excess macronutrients (nitrate and phosphorous), intercepting the runoff from agricultural areas before it reaches the water course. The Poplars can also be used as "water pumps" to minimize or prevent groundwater and plume migration from contaminated areas (phytostabilization) (De paolis et al., 2011).

Phytotechnologies applications Experimental studies

Di Lonardo, S., Capuana, M., Arnetoli, M., Gabbrielli, R., & Gonnelli, C. (2011). Exploring the Reference metal phytoremediation potential of three L. clones using an in vitro screening. Environmental Science and Pollution Research, 18(1), 82-90.

one commercial and two autochthonous P. alba Species and varieties clones: Villafranca (Vil), Fiorentini (Frt) and Querce (Qrc), respectively. Contaminants of concern arsenic, cadmium, copper, and zinc Mechanism involved in phytoremediation: Phytostabilisation/rhizodegradation/phyt Phytoaccumulation oaccumulation/phytodegradation/phytov olatilization/ hydraulic control/ tolerant

Types of microorganisms Not reported in the publication associated with the plant Requirements for phytoremediation Not reported in the publication (specific nutrients, addition of oxygen)

Laboratory/field experiment in vitro screening

Length of experiment 5 weeks

Well-developed shoots were cut at uniform size from pre-cultivated (two internodes; 1.5-cm Age of plant at 1st exposure tall) and transferred to phytohormones-free WPM (seed, post-germination, mature) medium containing the contaminants at different concentrations. phytohormone-free WPM medium containing a Substrate characteristics series of different concentration of contaminants.

Na2HAsO4 (0, 5, 50 and 250 μM) Initial contaminant concentration CuSO4 (0, 5, 50 and 250 μM), of the substrate CdSO4 (0, 5, 50 and 250 μM)

ZnSO4 (0, 250, 1,000 and 2,000 μM)

Phytotechnologies applications

Post-experiment contaminant No reported concentration of the substrate In all clones, a significant negative effect of metal treatment on root dry biomass was shown only at the highest concentration for arsenic and zinc treatments. The reduction in dry biomass due to the presence of cadmium in the culture medium was always significant in the Vil clone, whereas no effect was detected in the other two clones. The clones displayed a very strong root growth inhibition at the highest copper concentrations, showing roots so reduced to be excluded from the Post-experiment plant condition analysis, while the lower concentrations had no significant effect. The highest values of root dry biomass were always significantly shown by the Vil clone, except in the case

of cadmium treatment. In all clones, roots were significantly more affected by metal toxicity than shoots. In fact, even if a decrease in the weight of shoot dry biomass was shown for some metal treatments, it was never significant in this plant organ. Although in all plants, the metal concentration in the Contaminant storage sites in the tissues increased with the external metal plant and contaminant concentration, and metal concentrations were concentrations in tissues generally higher in roots than in shoots, the three (root, shoot, leaves, no storage) clones differed significantly in root and shoot metal accumulation and content.