Root Porosity Changes in <Emphasis Type="Italic">Salix nigra</Emphasis> Cuttings in Response to Copper and Ultraviolet-B Radiation Exposure

Cuttings of black willow (Salix nigra), a naturally occurring wetland species, are used for restoration and streambank stabilization. As an adaptation to their wetland habitat, this species develops aerenchyma tissue to avoid root anoxia. To determine the effects of combined copper and ultraviolet-B radiation exposure on aerenchyma tissue (measured as root porosity), black willow cuttings were grown hydroponically and exposed to three ultraviolet-B (UV-B) intensities and three Cu concentrations in a completely randomized 3?×?3 factorial design. While both UV-B (F _2,42?=?11.45; p?=?0.0001) and Cu (F _2,42?=?6.14; p?=?0.0046) exposure increased root porosity, total biomass decreased in response to both UV-B (F _2,43?=?3.36; p?=?0.0441) and to Cu (F _2,43?=?4.03; p?=?0.0249). Root biomass decreased only in response to Cu (F _2,41?=?3.41; p?=?0.0427) resulting in a decrease in the root/shoot ratio (F _2,42?=?3.5; p?=?0.0393). Copper exposure also resulted in a decrease in the number of leaves/shoot (F _2,42?=?7.03; P?=?0.0023). No UV-B and Cu interaction was found. While the present research indicates the negative effects of Cu contamination and elevated UV-B intensities on S. nigra, it also points out potential mechanisms that S. nigra uses to alleviate these stresses.