Rathcke Beverly J
Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan 48109-1048 USA.
Am J Bot. 2003 Sep;90(9):1328-32. doi: 10.3732/ajb.90.9.1328.
Floral longevity is assumed to reflect a balance between the benefit of increased pollination success and the cost of flower maintenance. Flowers of Kalmia latifolia (Ericaceae), mountain laurel, have a long duration and can remain viable up to 21 d if unpollinated. I experimentally tested whether this long duration increases pollination success by clipping stigmas to reduce functional floral longevity to 3-4 d. Clipping stigmas decreased fruit set from 65% to only 10%. Flowers with natural life spans were not pollination-limited, demonstrating that long floral duration ensured female reproductive success. The long floral duration of K. latifolia was unique in this site (the Great Swamp, Rhode Island, USA). Coflowering shrubs in summer had a mean floral life span of 3.4 d. Spring-flowering species had significantly longer mean floral durations (7.2 d). These duration differences may reflect seasonal variation in pollinator availability. However, K. latifolia flowers in summer, when its bumble bee pollinators are abundant but it is a poor competitor for bees because its flowers produce little nectar. The long floral duration allows K. latifolia to outlast coflowering competitors and attract sufficient pollinators. I hypothesize that the long floral duration of K. latifolia functions as a mechanism for competitive avoidance and reproductive assurance.
花期长短被认为反映了授粉成功率提高带来的益处与花朵维持所需成本之间的平衡。山月桂（杜鹃花科）的花朵花期较长，如果未授粉，可持续存活长达21天。我通过实验测试了这种较长的花期是否能提高授粉成功率，方法是剪掉柱头，将花朵的有效花期缩短至3 - 4天。剪掉柱头后，坐果率从65%降至仅10%。具有自然寿命的花朵不存在授粉限制，这表明较长的花期确保了雌性生殖成功。山月桂较长的花期在该地点（美国罗德岛大沼泽地）是独特的。夏季同时开花的灌木平均花期为3.4天。春季开花的物种平均花期明显更长（7.2天）。这些花期差异可能反映了传粉者可利用性的季节性变化。然而，山月桂在夏季开花，此时其传粉者大黄蜂数量众多，但它在吸引蜜蜂方面竞争力较弱，因为其花朵产生的花蜜很少。较长的花期使山月桂能够比同时开花的竞争者花期更长，并吸引到足够的传粉者。我推测山月桂较长的花期起到了竞争回避和繁殖保障的作用。
