Torres-Martínez Lorena, Weldy Phillip, Levy Morris, Emery Nancy C
Department of Biological Sciences, Purdue University, 915 W. State Street, West Lafayette, IN 47907-2054, USA.
Department of Ecology and Evolutionary Biology, University of Colorado Boulder, Campus Box 334, University of Colorado, Boulder, CO 80309-0334, USA
Ann Bot. 2017 Jan;119(2):253-265. doi: 10.1093/aob/mcw161. Epub 2016 Aug 21.
Many locally endemic species in biodiversity hotspots are restricted to edaphic conditions that are fixed in the landscape, limiting their potential to track climate change through dispersal. Instead, such species experience strong selection for germination strategies that can track suitable conditions through time. Germination strategies were compared among populations across the geographic range of a California vernal pool annual, Lasthenia fremontii Local germination strategies were tested to determine the associations with geographic variation in precipitation patterns.
This study evaluated patterns of seed germination, dormancy and mortality in response to simulated variation in the timing, amount and duration of the first autumn precipitation event using seeds from six populations that span a geographic gradient in precipitation. Next, it was tested whether the germination strategies of different populations can be predicted by historical precipitation patterns that characterize each site.
A significant positive relationship was observed between the historical variability in autumn precipitation and the extent of dormancy in a population. Marginal populations, with histories of the most extreme but constant autumn precipitation levels, expressed the lowest dormancy levels. Populations from sites with historically higher levels of autumn precipitation tended to germinate faster, but this tendency was not statistically significant.
Germination in L. fremontii is cued by the onset of the first rains that characterize the beginning of winter in California's Great Central Valley. However, populations differ in how fast they germinate and the fraction of seeds that remain dormant when germination cues occur. The results suggest that seed dormancy may be a key trait for populations to track increasingly drier climates predicted by climate change models. However, the low dormancy and high mortality levels observed among seeds of the southernmost, driest populations make them most vulnerable to local extinction.
生物多样性热点地区的许多本地特有物种局限于固定在景观中的土壤条件，这限制了它们通过扩散追踪气候变化的潜力。相反，这类物种在萌发策略上经历了强烈的选择，以便能够随时间追踪适宜的条件。对加利福尼亚州春季池塘一年生植物弗氏拉氏草（Lasthenia fremontii）地理分布范围内不同种群的萌发策略进行了比较。测试了当地的萌发策略，以确定其与降水模式地理变异的关联。
本研究使用来自六个跨越降水地理梯度的种群的种子，评估了种子萌发、休眠和死亡率对模拟的首次秋季降水事件的时间、数量和持续时间变化的响应模式。接下来，测试了不同种群的萌发策略是否可以通过表征每个地点的历史降水模式来预测。
观察到秋季降水的历史变异性与种群休眠程度之间存在显著的正相关关系。边缘种群经历了最极端但稳定的秋季降水水平，其休眠水平最低。历史上秋季降水水平较高地点的种群往往萌发更快，但这种趋势在统计学上并不显著。
弗氏拉氏草的萌发由加利福尼亚州中央大谷地冬季开始时的第一场降雨引发。然而，不同种群在萌发速度以及萌发信号出现时保持休眠的种子比例方面存在差异。结果表明，种子休眠可能是种群追踪气候变化模型预测的日益干燥气候的关键特征。然而，在最南端、最干燥种群的种子中观察到的低休眠和高死亡率水平使它们最容易面临局部灭绝。
