USDA-ARS Pest Management Research Unit, Northern Plains Agricultural Research Laboratory, Sidney, Montana, 59270, USA.
School of Biological Sciences, University of Nebraska, Lincoln Nebraska, 68588-0118, USA.
Am J Bot. 2021 Oct;108(10):1889-1901. doi: 10.1002/ajb2.1744. Epub 2021 Oct 19.
Plants experiencing steep reproductive losses from herbivores should favor strategies promoting tolerance or resistance to that herbivory. However, the degree to which such strategies succeed in improving plant fitness under natural conditions needs further evaluation, especially for iterocarpic species. We tested whether reproductive effort by the iterocarpic Cirsium undulatum Spreng. (Wavyleaf thistle) provided within-season tolerance for floral herbivory through response to apical damage.
We imposed apical damage and manipulated floral herbivory on later-flowering, non-apical flowerheads for two seasons. We asked: (1) is there evidence of compensatory potential to tolerate apical flowerhead damage? If so, (2) does the amount of herbivore pressure on non-apical flowerheads influence the magnitude of any compensatory response; and (3) is the response to apical damage sufficient to increase plant seed production under ambient floral herbivory over the flowering season?
Plants showed compensatory potential for apical head loss; apical damage increased seed contributions from later, lower positioned flowerheads. Further, the intensity of subsequent herbivore pressure influenced compensation outcomes. Equitable seed production under both levels of ambient herbivory occurred only in the year in which plants were larger and insect pressure was lower. Finally, the response to apical damage was sufficient to compensate for apical seed loss, but it did not consistently increase overall annual seed production under ambient floral herbivory.
Although this iterocarpic species can compensate for apical damage, tolerance for floral herbivory varied between years.
遭受食草动物严重繁殖损失的植物应倾向于促进对这种食草性的耐受性或抗性的策略。然而，在自然条件下，这些策略在多大程度上成功地提高了植物的适应性仍需进一步评估，尤其是对于雌雄异熟的物种。我们通过对顶梢损伤的反应，测试了雌雄异熟的皱叶蓟（Wavyleaf thistle）是否通过生殖努力提供了对花期食草性的耐受力。
我们在两个季节对后期开花的非顶梢花头施加顶梢损伤并操纵花部食草性。我们问：（1）是否有证据表明存在耐受顶梢花头损伤的补偿潜力？如果有，（2）非顶梢花头的食草压力大小是否会影响任何补偿反应的程度；（3）对顶梢损伤的反应是否足以在整个花期的环境花部食草性下增加植物的种子产量？
植物对顶梢损失表现出补偿潜力；顶梢损伤增加了后来位于较低位置的花头的种子贡献。此外，后续食草压力的强度影响了补偿结果。在两种环境食草压力下都实现公平的种子产量仅发生在植株较大且昆虫压力较低的那一年。最后，对顶梢损伤的反应足以补偿顶梢种子的损失，但在环境花部食草性下，它并不总能持续增加植物的总年度种子产量。
尽管这种雌雄异熟的物种可以补偿顶梢损伤，但对花部食草性的耐受性在不同年份有所不同。
