Water-Use Dynamics of an Invasive Reed, Arundo donax, from Leaf to Stand

We investigated water use of an invasive riparian reed species, Arundo donax (L.), along moisture gradients to determine how extensively this plant might affect water resources. On an approximately 250 m stretch of the Lower Rio Grande in South Texas, we measured the gas exchange of water vapor at the leaf scale and structural characteristics, such as leaf area and shoot density, at the stand scale. To assess the effect of water availability, we used transects perpendicular to the edge of the river along a potential moisture gradient. Stands of A. donax used approximately 8.8+/-0.9 mm of water per day during the peak of the 2008 growing season; this rate of water use is at the high end of the spectrum for plants. Transpiration and leaf area index varied with water availability, which suggests this plant is sensitive to drought and declining water tables. This provides a baseline for future studies comparing water use between A. donax and other plant species, especially native species considered in riparian restoration efforts.