Liyanage Ganesha S, Ooi Mark K J
Centre for Sustainable Ecosystem Solutions, School of Biological Sciences, University of Wollongong, Wollongong, NSW 2522, Australia
Centre for Sustainable Ecosystem Solutions, School of Biological Sciences, University of Wollongong, Wollongong, NSW 2522, Australia.
Ann Bot. 2015 Jul;116(1):123-31. doi: 10.1093/aob/mcv069. Epub 2015 May 21.
Intra-population variation in seed dormancy is an advantage for population persistence in unpredictable environments. The important role played by physically dormant species in these habitats makes understanding the level of variation in their dormancy a key ecological question. Heat produced in the soil is the major dormancy-breaking stimulus and, in fire prone ecosystems, soil temperatures generated by fire may vary spatially and over time. While many studies have investigated variation in initial dormancy, a measure that is of little value in fire-prone ecosystems, where initial dormancy levels are uniformly high, intra-population variation in dormancy-breaking temperature thresholds has never been quantified. This study predicted that species would display variation in dormancy-breaking temperature thresholds within populations, and investigated whether this variation occurred between individual plants from the same maternal environment.
The intra-population variation in dormancy-breaking thresholds of five common physically dormant shrub species (family Fabaceae) from fire-prone vegetation in south-eastern Australia was assessed using heat treatments and germination trials. Replicate batches of seeds from each of four maternal plants of Dillwynia floribunda, Viminaria juncea, Bossiaea heterophylla, Aotus ericoides and Acacia linifolia were treated at 40, 60, 80, 100 and 120 °C.
Dormancy-breaking response to heat treatments varied significantly among individual plants for all species, with some individuals able to germinate after heating at low temperatures and others restricting germination to temperatures that only occur as a result of high-severity fires. Germination rate (T50) varied among individuals of three species.
Variation detected among individuals that were in close proximity to each other indicates that strong differences in dormancy-breaking temperature thresholds occur throughout the broader population. Differences found at the individual plant level could contribute to subsequent variation within the seed bank, providing a bet-hedging strategy, and represent a mechanism for increasing the probability of population persistence in the face of fire regime variability.
种子休眠的种群内变异有利于种群在不可预测的环境中持续存在。物理休眠物种在这些栖息地中发挥的重要作用使得了解其休眠变异水平成为一个关键的生态学问题。土壤中产生的热量是主要的打破休眠的刺激因素，在易发生火灾的生态系统中，火灾产生的土壤温度可能会随空间和时间而变化。虽然许多研究调查了初始休眠的变异，但在初始休眠水平普遍较高的易发生火灾的生态系统中，这一指标价值不大，而打破休眠温度阈值的种群内变异从未被量化。本研究预测物种在种群内会表现出打破休眠温度阈值的变异，并调查这种变异是否发生在来自相同母本环境的个体植物之间。
利用热处理和发芽试验评估了澳大利亚东南部易发生火灾植被中五种常见的物理休眠灌木物种（豆科）打破休眠阈值的种群内变异。对来自多花迪尔维尼亚、细叶决明、异叶博西亚、埃里克奥图斯相思和线叶金合欢四种母本植物的种子重复批次进行40、60、80、100和120°C的处理。
所有物种的个体植物对热处理的打破休眠反应差异显著，一些个体在低温加热后能够发芽，而另一些个体则将发芽限制在只有高强度火灾才会出现的温度下。三种物种的个体之间发芽率（T50）有所不同。
在彼此相邻的个体之间检测到的变异表明，在更广泛的种群中存在打破休眠温度阈值的强烈差异。在个体植物水平上发现的差异可能导致种子库内随后的变异，提供一种风险分摊策略，并代表一种在火灾发生模式多变的情况下增加种群持续存在概率的机制。
