Ecohydrology and ecophysiology of Arundo donax (giant reed) in response to herbivory and drought

Background/Question/Methods

Arundo donax is a non-native species that can form dense monocultural stands along waterways throughout the southern half of the United States, including much of the Rio Grande watershed. Although it is often assumed to be a large consumer of water, data quantifying transpiration at any scale in this species are lacking. Furthermore, information on Arundo’s responses to stressors such as herbivory, drought, and nutrient limitation is needed. A main objective of this research is to estimate large scale water use and productivity of Arundo donax from leaf-scale measurements of transpiration (E_l) and photosynthesis (A_l) in combination with allometric data on leaf area and biomass. The reliability of this estimate is enhanced by incorporating spatial (lateral and vertical) as well as temporal variation within established stands. Additional greenhouse work has evaluated the efficacy of two potential biological control agents (a gall wasp, Tetramesa romana, and an armored scale, Rhizaspidiotus donacis) by measuring how each insect affected E_l and A_l.

Results/Conclusions

Peak rates of E_l and A_l occurred in late July and were 9.29 mmol H₂O m^-2 s^-1 and 28.3 μmol CO₂ m^-2 s^-1, respectively. Stand-scale estimates were highly dependent on leaf area index (LAI), which also peaked mid-season at 8.8 m² m^-2. Initial measurements showed that E_l was reduced by 15% and 25% and A_l may be reduced by 13% and 20% by T. romana and R. donacis, respectively. This research presents an important step towards predicting Arundo water use under the wide range of growing conditions in the Rio Grande basin as well as towards finding an effective biological control agent.