@article{petzold_brownie_gould_2009, title={Effect of Heliothis subflexa herbivory on fruit abscission by Physalis species: the roles of mechanical damage and chemical factors}, volume={34}, ISSN={["1365-2311"]}, DOI={10.1111/j.1365-2311.2009.01109.x}, abstractNote={Abstract. 1. Insect oral secretions are important for the induction of a number of plant responses, but the relative role of mechanical damage in the induction of these responses is often not well understood. Damage from the frugivore Heliothis subflexa , a specialist on Physalis species, causes herbivore‐induced fruit abscission. In this field study, we examined the separate and combined effects of mechanical damage and H. subflexa oral secretions on Physalis fruit abscission. 2. To determine the relative role of mechanical and chemical factors, the following treatments were administered to fruit: (1) three levels of mechanical damage, (2) natural herbivore damage by control larvae and by larvae surgically treated to inhibit saliva secretion, and (3) injection of H. subflexa oral secretions and a water control. Abscission of mechanically damaged fruit with and without the addition of oral secretions was also compared. 3. Mechanical damage was sufficient to cause fruit abscission, and the addition of oral secretions to mechanically damaged fruit did not cause an increase in fruit abscission. Normal caterpillars and those treated to inhibit saliva secretion caused similar abscission rates. 4. Though most studies examining the effects of insect oral secretions on induced plant responses find these chemical stimuli to be important or essential, the results of the present study showed that oral secretions are not necessary for fruit abscission. Future work is needed to determine the relative importance of mechanical damage in herbivore‐induced plant responses in other systems.}, number={5}, journal={ECOLOGICAL ENTOMOLOGY}, author={Petzold, Jennifer and Brownie, Cavell and Gould, Fred}, year={2009}, month={Oct}, pages={603–613} }
 @article{stinson_tranz_petzold_bazzaz_2006, title={Architectural and physiological mechanisms of reduced size inequality in CO2-enriched stands of common ragweed (Ambrosia artemisiifolia)}, volume={12}, ISSN={["1354-1013"]}, DOI={10.1111/j.1365-2486.2006.01229.x}, abstractNote={Abstract Testing whether and how subordinate individuals differ from dominants in the utilization of enriched CO 2 atmospheres is important for understanding future stand and community structure. We hypothesized that subordinate and dominant Ambrosia artemisiifolia L. (Asteraceae) (common ragweed) plants growing in dense stands would not equally acquire or utilize carbon gains from CO 2 ‐enrichment, and that the resulting disproportionate growth gains to subordinates would reduce size inequalities in competing stands. We grew experimental stands of A. artemisiifolia in either ambient (360 μL L −1 ) or twice ambient (720 μL L −1 ) levels of atmospheric CO 2 . We compared the relative growth, photosynthetic capacity, and architecture of subordinate and dominant plants in each treatment, and assessed size inequalities using the stand‐level coefficient of variation (CV). In elevated CO 2 , plants grew larger, but subordinate plants shifted more mass to upper stem allocation than dominants. Dominant plants demonstrated reduced leaf‐level photosynthetic gains in elevated CO 2 compared with subordinate plants. Reduced CVs in plant size reflected smaller proportional growth gains by dominants over subordinates in elevated vs. ambient stands. We conclude that differences in the architectural and physiological responses of subordinate and dominant ragweed plants reduce competition and allow subordinate plants to catch up to dominants in elevated CO 2 conditions.}, number={9}, journal={GLOBAL CHANGE BIOLOGY}, author={Stinson, Kristina A. and Tranz, Jimmy H. and Petzold, Jennifer L. and Bazzaz, F. A. .}, year={2006}, month={Sep}, pages={1680–1689} }