Ecophysiological responses of salt cedar (Tamarix spp. L.) to the northern tamarisk beetle (Diorhabda carinulata Desbrochers) in a controlled environment

Abstract

The northern tamarisk beetle (Diorhabda carinulata Desbrochers) was released in several western states as a biocontrol agent to suppress Tamarix spp. L. which has invaded riparian ecosystems; however, effects of beetle herbivory on Tamarix physiology are largely undocumented and may have ecosystem ramifications. Herbivory by this insect produces discoloration of leaves and premature leaf drop in these ecosystems, yet the cause of premature leaf drop and the effects of this leaf drop are 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 drop may affect plant tissue chemistry and belowground carbon allocation. We conducted a greenhouse experiment to understand how Tamarix responds physiologically to adult beetle and larvae herbivory and to determine the proximate cause of premature leaf drop. We hypothesized that plants experiencing beetle herbivory would have greater leaf and root respiration rates, greater photosynthesis, increased water stress, inefficient leaf nitrogen retranslocation, 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 drop 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 plants subjected to herbivory. Stress induced by herbivory may render these trees less competitive in future growing seasons.

Insect biological control accelerates leaf litter decomposition and alters short‐term nutrient dynamics in aTamarix‐invaded riparian ecosystem

“…Trees that suffer multiple years of herbivory would likely produce declining amounts of new leaves, and thus less litter through time. Results of this study and a related study in controlled greenhouse conditions (Snyder et al in press) indicated that Tamarix exposed to beetle herbivory were inefficient at conserving leaf nutrients before premature leaf drop. This idea is supported by Hudgeons et al (2007), who found that spring aboveground growth was reduced by 35% on Tamarix trees that were defoliated by beetles the previous fall in a manipulative field cage experiment in Texas and that carbohydrate concentrations were decreased in Tamarix root tissue over several years of defoliation in a field study near Lovelock, Nevada.…”

“…Feeding by adult and larval stages of the beetle on the live leaf tissue of Tamarix causes the leaves to rapidly discolor and desiccate, and then fall from the tree during the normal summer growing season. Beetle herbivory results in damage to the leaf from scraping and chewing, as well as removal of whole sections of leaves (Snyder et al in press). The proximate cause of premature leaf drop is likely irreversible desiccation resulting from herbivore‐induced leaf wounding that reduces the plant's ability to regulate water loss (Snyder et al in press).…”

“…Beetle herbivory results in damage to the leaf from scraping and chewing, as well as removal of whole sections of leaves (Snyder et al in press). The proximate cause of premature leaf drop is likely irreversible desiccation resulting from herbivore‐induced leaf wounding that reduces the plant's ability to regulate water loss (Snyder et al in press). This accelerated senescence may truncate the process of retranslocation of nutrients that normally occurs during natural leaf senescence, and would likely result in leaf litter of higher nutrient content (Hunter 2001, Chapman et al 2003).…”

Semiochemicals to enhance herbivory by Diorhabda carinulata aggregations in saltcedar (Tamarix spp.) infestations

“…These feeding activities damage leaf surface structures, resulting in compromised water regulation in affected plants. Impaired water regulation results in desiccation and ultimately defoliation of the plant . Feeding by D. carinulata can dramatically increase stress on plants, potentially reducing carbon storage, impairing leaf production and reducing root mass in the years following a defoliation event .…”

Longer term effects of biological control on tamarisk evapotranspiration and carbon dioxide exchange

“…Beetle herbivory produced greater transpiration per unit leaf area for tamarisk along the Walker River, Nevada, but these phenomena were not observed for tamarisk along the Humboldt River, Nevada (Pattison, D'Antonio, Dudley, Allander, & Rice, ). Snyder et al () in a greenhouse experiment also found greater transpiration per unit leaf area, but decreased photosynthetic rates, after beetle herbivory and before premature leaf drop. Taken together, there is little evidence for photosynthetic compensation in the remaining leaves.…”