Ooi Mark K J, Auld Tony D, Whelan Robert J
Institute for Conservation Biology, School of Biological Sciences, University of Wollongong, NSW 2522, Australia.
Ann Bot. 2006 Aug;98(2):421-30. doi: 10.1093/aob/mcl118. Epub 2006 May 30.
Germination studies of species from fire-prone habitats are often focused on the role that fire plays in breaking dormancy. However, for some plant groups in these habitats, such as the genus Leucopogon (Ericaceae), dormancy of fresh seeds is not broken by fire cues. In the field, these same species display a flush of seedling emergence post-fire. Dormancy and germination mechanisms therefore appear complex and mostly unknown. This study aimed to identify these mechanisms by establishing dormancy class and testing the effects of a set of typical germination cues, including those directly related to fire and entirely independent of fire.
To classify dormancy, we assessed seed permeability and embryo morphology, and conducted germination experiments at seasonal temperatures in incubators. To test the effects of fire cues on germination, factorial combinations of smoke, heat and dark treatments were applied. Ageing treatments, using burial and seasonal incubation, were also tested. Germination phenology was established.
Seeds were dormant at release and had underdeveloped embryos. Primary dormancy of the study species was classified as morphophysiological. Seasonal temperature changes overcame primary dormancy and controlled timing of germination. Fire cues did not break primary dormancy, but there was a trend for smoke to enhance germination once this dormancy was overcome.
Despite the fact that fire is a predominant disturbance and that many species display a flush of emergence post-fire, seasonal temperatures broke the primary physiological dormancy of the study species. It is important to distinguish between fire being responsible for breaking dormancy and solely having a role in enhancing levels of post-fire germination for seeds in which dormancy has been overcome by other factors. Biogeographical evidence suggests that morphological and physiological factors, and therefore seasonal temperatures, are likely to be important in controlling the dormancy and patterns of post-fire germination of many species in fire-prone regions.
对来自易发生火灾栖息地的物种进行的萌发研究，通常聚焦于火灾在打破休眠中所起的作用。然而，对于这些栖息地中的一些植物类群，比如澳石南属（杜鹃花科），新鲜种子的休眠不会被火灾信号打破。在野外，这些相同的物种在火灾后会出现幼苗集中出土的现象。因此，休眠和萌发机制似乎很复杂且大多未知。本研究旨在通过确定休眠类别并测试一组典型萌发信号（包括那些与火灾直接相关以及完全与火灾无关的信号）的影响来识别这些机制。
为了对休眠进行分类，我们评估了种子的透性和胚的形态，并在培养箱中模拟季节性温度进行萌发实验。为了测试火灾信号对萌发的影响，我们采用了烟雾、加热和黑暗处理的析因组合。还测试了通过掩埋和季节性培养进行的老化处理。确定了萌发物候。
种子在散落时处于休眠状态且胚发育不全。研究物种的初级休眠被归类为形态生理休眠。季节性温度变化克服了初级休眠并控制了萌发时间。火灾信号并未打破初级休眠，但一旦这种休眠被克服，有烟雾增强萌发的趋势。
尽管火灾是主要的干扰因素，且许多物种在火灾后会出现集中出土的现象，但季节性温度打破了研究物种的初级生理休眠。区分火灾是负责打破休眠还是仅仅在增强已被其他因素打破休眠的种子的火灾后萌发水平方面发挥作用很重要。生物地理学证据表明，形态和生理因素以及因此的季节性温度，可能在控制易发生火灾地区许多物种的休眠和火灾后萌发模式方面很重要。
