Seasonal variation of responses to herbivory and volatile communication in sagebrush (Artemisia tridentata) (Asteraceae)
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Plants can respond to insect herbivory in various ways to avoid reductions in fitness. However, the effect of herbivory on plant performance can vary depending on the seasonal timing of herbivory. We investigated the effects of the seasonal timing of herbivory on the performance of sagebrush (Artemisia tridentata). Sagebrush is known to induce systemic resistance by receiving volatiles emitted from clipped leaves of the same or neighboring plants, which is called volatile communication. Resistance to leaf herbivory is known to be induced most effectively after volatile communication in spring. We experimentally clipped 25 % of leaves of sagebrush in May when leaves were expanding, or in July when inflorescences were forming. We measured the growth and flower production of clipped plants and neighboring plants which were exposed to volatiles emitted from clipped plants. The treatment conducted in spring reduced the growth of clipped plants. This suggests that early season leaf herbivory is detrimental because it reduces the opportunities for resource acquisition after herbivory, resulting in strong induction of resistance in leaves. On the other hand, the late season treatment increased flower production in plants exposed to volatiles, which was caused mainly by the increase in the number of inflorescences. Because the late season treatment occurred when sagebrush produces inflorescences, sagebrush may respond to late herbivory by increasing compensation ability and/or resistance in inflorescences rather than in leaves. Our results suggest that sagebrush can change responses to herbivory and subsequent volatile communication seasonally and that the seasonal variation in responses may reduce the cost of induced resistance.
KeywordsHerbivory Induced resistance Optimal defense theory Phenological differences Volatile communication Tolerance
We thank Jeff Brown for permission to work at the UC Sagehen Creek Reserve in Tahoe National Forest; Gen-ichiro Arimura and Makiko Kawakami for assistance for our field work; Jesse Karban for assistance for laboratory work. This research was supported by Grand-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (JSPS) (23405007, 23770020), research fellowships of the JSPS for Young Scientists to S. Ishizaki and K. Shiojiri, the Clark Memorial Foundation to S. Ishizaki, the Sasakawa Scientific Research Grant from The Japan Science Society, The Naito Foundation Subsidy for Female Researchers after Maternity Leave to K. Shiojiri, Grand for Promotion of Niigata University Research Projects, and the Ministry of Education, Culture, Sports, Science and Technology of Japan for Global Centers of Excellence Program (J01).
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