Giant Reed

Appearance

"Arundo donax" generally grows to 6 metres in height, or in ideal conditions can exceed 10 metres. The hollow stems are 2 to 3 centimetres in diameter. The grey-green swordlike leaves are alternate, 30 to 60 centimetres long and 2 to 6 centimetres wide with a tapered tip, and have a hairy tuft at the base. Overall, the plant resembles an outsize common reed or a bamboo .

"Arundo donax" flowers in late summer, bearing upright, feathery plumes 40 to 60 centimetres 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 deep . Stem and rhizome pieces less than 5 centimetres long and containing a single node could sprout readily under a variety of conditions . 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 .

Behavior

"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.Rossa B, TuAers AV, Naidoo G, von Willert DJ. 1998. "Arundo donax" L. —a C3 species with unusually high photosynthetic capacity. Botanica Acta. 111:216–21.

Habitat

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.

Uses

When young, "A. donax" is readily browsed by ruminants, but it becomes unpalatable when maturing. "A. donax" has also been used in constructed wetlands for wastewater treatment.