Crone Elizabeth E, Lesica Peter
Wildlife Biology Program and Department of Ecosystem and Conservation Sciences, University of Montana, Missoula, MT 59802, USA.
Oecologia. 2006 Nov;150(1):40-9. doi: 10.1007/s00442-006-0506-0. Epub 2006 Aug 31.
Mast seeding is common in plant populations, but its causes have rarely been tested experimentally. We tested mechanisms of alternate-year flowering and fruit set in an iteroparous, bee-pollinated, herbaceous plant, Astragalus scaphoides, in semi-arid sagebrush steppe. Patterns of reproduction from 1986 to 1999 indicated that spring precipitation was a cue for synchronous flowering, and that increased pollination in high-flowering years was a fitness advantage of synchrony. We tested these patterns by adding supplemental water and pollen to plants in high- and low-flowering sites and years. Supplemental water had no effect on flowering or seed set, so water is not a proximate cue for reproduction, though it could be important over longer (>3 year) time scales. Supplemental pollination increased fruit set in low- but not high-flowering years, indicating that synchronous flowering increases pollination success. Many shorter-term studies also report increased fruit set after pollen supplementation, but not after resource addition. This pattern may reflect the fact that plants can store and reallocate resources, but not pollen, across multiple years. For animal-pollinated herbs such as these, uniting theories about pollination ecology and mast seeding may promote an understanding of the mechanisms that determine patterns of reproduction over time.
大年结实现象在植物种群中很常见，但其成因很少经过实验验证。我们对半干旱的蒿属草原中一种多年生、蜜蜂传粉的草本植物——舟状黄芪交替开花和结果的机制进行了测试。1986年至1999年的繁殖模式表明，春季降水是同步开花的一个线索，而在高开花年份增加授粉是同步开花的一个适合度优势。我们通过在高开花和低开花地点及年份给植株补充水分和花粉来验证这些模式。补充水分对开花或结实没有影响，所以水分不是繁殖的直接线索，不过在更长（>3年）的时间尺度上它可能很重要。补充授粉在低开花年份增加了结实率，但在高开花年份没有，这表明同步开花提高了授粉成功率。许多短期研究也报告称补充花粉后结实率增加，但补充资源后则没有。这种模式可能反映了植物能够在多年间储存和重新分配资源，但不能储存和重新分配花粉这一事实。对于像这样的动物传粉草本植物，将传粉生态学理论和大年结实理论结合起来，可能有助于理解决定繁殖随时间变化模式的机制。
