Richardson Lea K, Beck Jared, Eck Daniel J, Shaw Ruth, Wagenius Stuart
Program in Plant Biology and Conservation, Northwestern University, 2205 Tech Drive, Hogan 6-140B, Evanston, Illinois, 60208, USA.
Negaunee Institute for Plant Conservation Science and Action, Chicago Botanic Garden, 1000 Lake Cook Road, Glencoe, Illinois, 60022, USA.
Am J Bot. 2023 Apr;110(4):e16160. doi: 10.1002/ajb2.16160. Epub 2023 Apr 17.
Fire induces flowering in many plant species worldwide, potentially improving reproductive fitness via greater availability of resources, as evident by flowering effort, and improved pollination outcomes, as evident by seed set. Postfire increases in flowering synchrony, and thus mating opportunities, may improve pollination. However, few studies evaluate fire effects on multiple components of fitness. Consequently, the magnitude and mechanism of fire effects on reproductive fitness remain unclear.
Over multiple years and prescribed burns in a prairie preserve, we counted flowering stems, flowers, fruits, and seeds of three prairie perennials, Echinacea angustifolia, Liatris aspera, and Solidago speciosa. We used aster life-history models to assess how fire and mating opportunities influenced annual maternal fitness and its components in individual plants.
In Echinacea and Liatris, but not in Solidago, fire increased head counts, and both fire and mating opportunities increased maternal fitness. Burned Echinacea and Liatris plants with many flower heads produced many seeds despite low seed set (fertilization rates). In contrast, plants with an average number of flower heads had high seed set and produced many seeds only when mating opportunities were abundant.
Fire increased annual reproductive fitness via resource- and pollination-dependent mechanisms in Echinacea and Liatris but did not affect Solidago fitness. The consistent relationship between synchrony and seed set implies that temporal mating opportunities play an important role in pollination. While fire promotes flowering in many plant species, our results reveal that even closely related species exhibit differential responses to fire, which could impact the broader plant community.
火灾会促使全球许多植物物种开花，通过增加资源可用性（如开花努力所示）以及改善授粉结果（如结实率所示），有可能提高繁殖适合度。火灾后开花同步性增加，进而交配机会增多，可能会改善授粉情况。然而，很少有研究评估火灾对适合度多个组成部分的影响。因此，火灾对繁殖适合度的影响程度和机制仍不清楚。
在一个草原保护区进行了多年的规定火烧实验，我们统计了三种草原多年生植物狭叶松果菊、粗糙蛇鞭菊和壮观一枝黄花的花茎、花朵、果实和种子数量。我们使用紫菀属植物生活史模型来评估火灾和交配机会如何影响个体植物的年度母本适合度及其组成部分。
在松果菊和蛇鞭菊中，而非一枝黄花中，火灾增加了头状花序数量，火灾和交配机会都提高了母本适合度。尽管结实率（受精率）较低，但具有许多头状花序的被火烧过的松果菊和蛇鞭菊植株仍产生了许多种子。相比之下，头状花序数量平均的植株结实率高，只有在交配机会充足时才会产生许多种子。
火灾通过依赖资源和授粉的机制提高了松果菊和蛇鞭菊的年度繁殖适合度，但对一枝黄花的适合度没有影响。同步性与结实率之间的一致关系表明，时间上的交配机会在授粉中起着重要作用。虽然火灾促进了许多植物物种的开花，但我们的结果表明，即使是亲缘关系密切的物种对火灾也表现出不同的反应，这可能会影响更广泛的植物群落。
