Effects of Insect Herbivory on Physiological and Biochemical (Oxidative Enzyme) Responses of the Halophyte <i>Atriplex subspicata</i> (Chenopodiaceae)

Physiological responses of the halophyte,Atriplex subspicataNutt. Rydb., to defoliation injurywere evaluated through a series of experimentsmeasuring plant gas exchange, ßuorometry, and enzymeactivity. Leaves exposed to simulated insect herbivory exhibited reductions in photosynthesis, stomatal conductance, and transpiration. Carboxylation efÞciency, maximum assimilation, and CO2 compensationwere alsonegatively associatedwithmechanical leaf injury. Insect injuryby aherbivore generalist, Spilosoma virginica, also reduced photosynthesis and carboxylation efÞciency within the saturated spectrum of A/Ci response curves. Initially, declines in photosynthesis occurred because of transient stomatal limitations.However, after time,mesophyll limitations impairedphotosynthesis and the plantÕs ability to compensate for injury. Fluorescence data and light assimilation responses indicated that defoliation did not play a role in limiting light reactions of photosynthesis. Enzyme analyses showed increased peroxidase activity with insect injury, suggesting the need for future characterization of oxidative enzymes, which have been associated with traits of resistance. Overall, we founda salt-tolerantplant tobe susceptible to insectherbivory throughareduction in theefÞciency of the plant to allocate energy resources. If salt tolerance comes at the cost of susceptibility to biotic interference, natural occurring halophytes or plants with transgenic salt tolerance may be at risk for heightened deleterious response to insect herbivory.