Submitted to: Biological Invasions
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/13/2010
Publication Date: 6/11/2010
Citation: Snyder, K.A., Uselman, S.M., Jones, T.J., Duke, S. 2010. Ecophysiological responses of salt cedar (Tamarix spp. L.) to the northern tamarisk beetle (Diorhabda carinulata Desbrochers) in a controlled environment. Biological Invasions. 12:3795-3808. Interpretive Summary: The leaf beetle, Diorhabda elongata, was released in several western states as a biocontrol agent to suppress Tamarix spp. L., commonly known as saltcedar, which has invaded many riparian ecosystems. Saltcedar has reduced native plant diversity, altered the hydrology of many river systems, changed fire behavior and in some case increased soil salinity in surface soils. Therefore, suppression of saltcedar is an issue of widespread importance. Since the initial releases, the leaf beetle successfully increased and spread to many miles of riparian habitat. However, the mechanism that produces the premature browning of leaves and early leaf drop was unknown. We conducted a greenhouse experiment to understand how saltcedar responds to herbivory by leaf beetle adults and larvae and to determine the proximate cause of premature leaf fall. Damage to the leaf tissue lead to excessive water loss by saltcedar plants and the apparent cause of leaf fall is extreme dessication.
Technical Abstract: The leaf beetle, Diorhabda elongata Brulle, was released in several western states as a biocontrol agent to suppress Tamarix spp. L. which has invaded riparian ecosystems; however, effects of leaf beetle herbivory on Tamarix physiology are largely undocumented and may have ecosystem ramifications. Herbivory by this insect produces discoloration of leaves and premature leaf fall in these ecosystems, yet the mechanism that promotes this is still unknown. Insect herbivory may change leaf photosynthesis and respiration and may affect a plant’s ability to regulate water loss and increase water stress. Premature leaf fall may affect plant tissue chemistry and belowground carbon allocation. We conducted a greenhouse experiment to understand how Tamarix responds to herbivory by leaf beetle adults and larvae and to determine the proximate cause of premature leaf fall. We hypothesized that herbivorized plants would have greater root and leaf respiration rates, greater photosynthesis, greater concentrations of leaf nitrogen and decreased retranslocation efficiency, increased water stress, lower root biomass and lower total non-structural carbohydrates in roots. Insect herbivory reduced photosynthesis rates, minimally affected respiration rates, but significantly increased water loss during daytime and nighttime hours and this produced increased water stress. The proximate cause for premature leaf fall appears to be desiccation. Plants exposed to herbivory were inefficient in their retranslocation of nitrogen before premature leaf drop. Root biomass showed a decreasing trend in herbivorized plants. Stress-induced by herbivory may render these trees less competitive in future growing seasons.