Seed germination is a critical stage in the life cycle of most plants and is defined by specific tolerance thresholds beyond which rates and success of germination rapidly decline. Previous studies have demonstrated that widespread plant species commonly germinate over a broad range of temperatures and water stress levels, whereas range-restricted species often exhibit a narrower germination window in terms of temperature and moisture. We investigated the relationships of the key germination traits of maximum germination (G max) and time to 50% germination (t 50) in response to temperature (5-35°C) and water stress (-1.5-0 MPa) in four co-occurring Western Australian native Eucalyptus species with widely varying biogeography. Eucalyptus caesia subsp. caesia and E. ornata exhibit a highly localized distribution and a narrow geographical range, being restricted either to granite outcrops or the upper slopes and tops of lateritic rises, respectively. These two species were compared with the two widespread and dominant congenerics E. salmonophloia and E. salubris. There was a distinctive hump-shaped response of t 50 to temperature and an exponential response to water stress, characteristic of rate- and threshold-limited processes, but no consistent pattern in the response of G max. The four species were significantly different in their thermal performance of t 50, with E. caesia and E. ornata displaying narrower thermal tolerance ranges than the two widespread species. In terms of mean final germination percentage, the two range-restricted endemic taxa exhibited higher lability in their response to thermal stress and drought stress compared to the two broadly distributed congenerics. These findings indicate a link between distributional extent, temperature and water stress tolerance and may have implications for identifying ecological filters of rarity and endemism.

中文翻译：

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西澳大利亚西南部四种同时存在的树种的种子的水文和热响应。

种子发芽是大多数植物生命周期中的关键阶段，由特定的耐受阈值定义，超过该阈值，发芽率和成功率会迅速下降。先前的研究表明，广泛的植物物种通常会在很宽的温度和水分胁迫水平下发芽，而受范围限制的物种在温度和湿度方面通常表现出较窄的发芽窗口。我们研究了在四个温度下响应温度（5-35°C）和水分胁迫（-1.5-0 MPa）时最大发芽（G max）和至50％发芽（t 50）的时间的关键发芽特性的关系。西澳大利亚州的原生桉树物种，生物地理分布广泛。桉树凯撒亚种。es树和大肠埃希菌（E. ornata）具有高度局部化的分布和狭窄的地理范围 仅限于花岗岩露头或红土上升的上坡和上坡。将这两个物种与两个广泛的和显性的同类E.salophophia和E. salubris进行了比较。t 50对温度有明显的驼峰形响应，对水分胁迫有指数响应，这是速率和阈值限制过程的特征，但在G max响应中没有一致的规律。这四个物种在t 50时的热性能显着不同，与两个广泛分布的物种相比，大肠埃希菌和大肠埃希菌显示的热耐受范围更窄。就平均最终发芽率而言，与两个分布广泛的同类植物相比，这两个范围受限制的地方性分类单元对热胁迫和干旱胁迫的反应表现出较高的不稳定性。