Arundo donax

Arundo donax, giant cane, is a tall perennial cane. It is one of several so-called reed species. It has several names including carrizo, arundo, Spanish cane, Colorado river reed, wild cane, and giant reed. Arundo donax grows in damp soils, either fresh or moderately saline, and is native to the Mediterranean Basin and Middle East, and probably also parts of Africa and the southern Arabian Peninsula. It has been widely planted and naturalised in the mild temperate, subtropical and tropical regions of both hemispheres (Herrera & Dudley 2003), especially in the Mediterranean, California, the western Pacific and the Caribbean. It forms dense stands on disturbed sites, sand dunes, in wetlands and riparian habitats. Arundo donax generally grows to 6 metres (20 ft) in height, or in ideal conditions can exceed 10 metres (33 ft). The hollow stems are 2 to 3 centimetres (0.79 to 1.18 in) in diameter. The grey-green swordlike leaves are alternate, 30 to 60 centimetres (12 to 24 in) long and 2 to 6 centimetres (0.79 to 2.36 in) wide with a tapered tip, and have a hairy tuft at the base. Overall, the plant resembles an outsize common reed (Phragmites australis) or a bamboo (subfamily Bambusoideae). Arundo donax flowers in late summer, bearing upright, feathery plumes 40 to 60 centimetres (16 to 24 in) long, that are usually seedless or with seeds that are rarely fertile. Instead, it mostly reproduces vegetatively by tough, fibrous underground rhizomes that form knotty, spreading mats which penetrate deep into the soil, up to 1 metre (3.3 ft) deep (Alden et al., 1998; Mackenzie, 2004). Stem and rhizome pieces less than 5 centimetres (2.0 in) long and containing a single node could sprout readily under a variety of conditions (Boose and Holt, 1999). This vegetative propagation appears well adapted to floods, which may break up individual A. donax clumps, spreading the pieces, which may sprout and colonise downstream (Mackenzie 2004). Arundo donax is a tall, perennial C3 grass in the subfamily Arundinoideae. Stems produced during the first growing season are unbranched and photosynthetic. In the Mediterranean, where a temperate climate is characterized by warm and dry summer and mild winter, new shoots of giant reed emerge around March, growing rapidly in June and July and producing stems and leaves. From late July the lower leaves start to dry, depending on seasonal temperature patterns. Drying accelerates during autumn when anthesis occurs from the beginning of October to the end of November. In this phenological stage moisture content falls significantly. In the low temperatures of winter giant reed stops its growth; regrowth occurs in springtime. Giant reed behaves as an annual in Central Europe where soil temperatures are low, due to poor freeze tolerance of the rhizomes. The base growth temperature reported for giant reed is 7 °C, with a maximum temperature of 30 °C. It has a high photosynthetic capacity, associated with absence of light saturation. Carbon dioxide exchange rates are high compared to other C3 and C4 species; maximum CO2 uptake ranged from 19.8 to 36.7 µmol m−2 s−1 under natural conditions, depending on irradiance and leaf age. Carbon dioxide exchange is regulated by leaf conductance. In most areas where giant reed grows (Mediterranean area and US), viable seeds are not produced. It is reported that sterility of giant reed results from failure of the megaspore mother cell to divide. This sterility, which drastically limits genetic variability, is an obstacle for breeding programs which aim to increase the productivity and biomass quality for energy conversion.A total of 185 clones of A. donax were collected from California to South Carolina and genetically fingerprinted with the SRAP and TE-based markers. Giant reed exhibited no molecular genetic variation despite the wide genomic coverage of the markers used in this study. The molecular data strongly point to a single genetic clone of A. donax in the United States, although multiple introductions of this plant into the United States have been documented. Another study conducted in the Mediterranean area sampled giant reed from 80 different sites, and demonstrated low gene diversity in this region as well. Results indicate the occurrence of post-meiotic alterations in the ovule and pollen developmental pathway. AFLP data support a monophyletic origin of giant reed and suggest that it originated in Asia, spreading from there into the Mediterranean Basin. Giant reed is adapted to a wide variety of ecological conditions, but is generally associated with riparian and wetland systems. It is distributed across the southern United States from Maryland to California. Plants can grow in a variety of soils, from heavy clays to loose sands and gravelly soils, but prefer wet drained soils, where they produce dense monotypic stands. Giant reed was found to grow rapidly in soil contaminated with arsenic, cadmium and lead; limited metal translocation from roots to shoots accounted for its strong tolerance to heavy metals. The same study determined that accumulations of As, Cd and Pb were high in roots but low in shoots, where SEM images showed thick and homogeneous stem tissue characteristics. In Pakistan, where the presence of arsenic has made risky the use of ground waters as a source of drinking water, a research study highlighted the phytoremediation potential of A. donax when grown in hydroponics cultures containing arsenic concentrations up to 1000 µg l−1. Giant reed was able to translocate the metals absorbed into the shoot and to accumulate metals in the stalk and leaves above the root concentration, showing no toxic effects at As concentrations up to 600 µg l−1. Furthermore, the plant is not consumed by herbivores, a positive trait in phytoremediation plants.