PARENT SESSION
Contributed Oral Session 102: Herbivory: Effects of Photosynthesis; Nutrients
Wednesday, August 10, 1:30 PM - 5:00 PM, Meeting Room 520 B, Level 5, Palais des congrès de Montréal
A seasonal pattern in Asclepias syriaca leaf photosynthetic responses to manually-imposed & actual insect herbivory.
Delaney, Kevin*,1, Haile, Fikru1, Peterson, Robert3, Higley, Leon4, 1 Xavier University of Louisiana, New Orleans, LA3 Montana State University, Bozeman, MT4 University of Nebraska-Lincoln, Lincoln, NE
ABSTRACT- Commonly, the photosynthetic response of a plant species is characterized by whether photosynthetic rates of remaining injured leaf tissue stay the same, increase, or decrease after leaf injury occurs. However, some species can have more than one of the above photosynthetic responses. Here, we present data from 26 experiments performed over a 9 year period with common milkweed, Asclepias syriaca (Asclepiadaceae). Each of these experiments examined leaf photosynthetic rate response to one or more of three types of leaf injury: actual herbivore tissue consumption, manually-imposed tissue removal, or the severing of the midrib vein. We found a seasonal pattern concerning whether or not photosynthetic rates were reduced on injured leaves for actual insect defoliation and manually-imposed defoliation. For all three types of injury, leaves tended to experience the largest reductions in photosynthetic rates when on stems with flowers and producing seed pods. However, leaves tended to experience low or no statistically significant reductions in photosynthetic rates on leaves of early emerging stems and on late season stems. Thus, we infer that A. syriaca reproductive phenology has an influence on individual leaf ability to maintain pre-injury photosynthetic rates following defoliation. This seasonal pattern may tied into reproductive resource trade-offs, or perhaps trade-offs related to the hormonal regulation of reproduction. Future experiments will be needed to test the mechanism causing seasonal variation in A. syriaca leaf photosynthetic response to herbivory, and may be applicable to more plant species as more examples of variation in photosynthetic responses are found within single plant species.
Key words: herbivory, phenology, photosynthesis, milkweed