Since climate change is expected to increase fire activity and drought stress in forests across the globe, studying seed resistance to heat stress and drought is imperative to predict future mountain forest regeneration scenarios. Here, stress co-occurrence and among population variation in stress resistance are key elements to consider. We hypothesized that i) increasing heat/osmotic stress intensity decreases germination performance; ii) seeds from higher elevations (i.e. cooler and wetter climatic conditions) exhibit lower resistance to heat/osmotic stress showing a stronger decline in germination performance as compared to seeds from lower elevations (i.e. warmer and drier climatic conditions); and that iii) elevational differences in seed stress resistance vary depending on whether stresses are applied alone or in combination. We exposed seeds from Polylepis australis and Escallonia cordobensis from low (1200 – 1400 m), mid (1650 – 1800 m) and high (2000 – 2200 m) elevational origins to different heat (control, 75, 105 °C) and osmotic (0, -0.3, -0.6 MPa polyethylene glycol) stress intensities. Germination performance decreased with increasing heat/osmotic stress intensity and clear differences among elevational origins were observed. In both species low-mid elevation seeds showed lowest performances but exhibited slightly higher stress resistance than high elevation seeds; yet the nature of these responses was species-specific. Our results demonstrate that germination response to a combination of heat stress and drought is different from the response to each of these stresses applied individually. Therefore, understanding how interactions of climate change with fire events can influence germination timing and success in mountain trees requires considering the effect of multiple stressors on seed physiology. Our findings also highlight the potential population-specific and species-specific responses, which could be used as guidance for ongoing restoration plans.

由于预计气候变化会增加全球森林的火源活动和干旱压力，因此研究种子对热胁迫和干旱的抵抗力对预测未来山区森林的再生情况势在必行。在这里，应同时考虑到压力共生和压力抗性的总体变化。我们假设i）增加热量/渗透胁迫强度会降低发芽性能；ii）与海拔较低（例如气候条件较干燥和干燥）的种子相比，海拔较高（例如气候条件较凉和潮湿）的种子对热/渗透胁迫的抵抗力较低，表现出更强的发芽性能下降；iii）种子抗逆性的高低差异取决于是单独施加还是联合施加。南方猪笼草和科尔多瓦草从低海拔（1200 – 1400 m），中海拔（1650 – 1800 m）和高海拔（2000 – 2200 m）到不同的热量（控制温度75、105°C）和渗透性（0，-0.3，-0.6 MPa聚乙烯）乙二醇）的应力强度。发芽性能随热/渗透胁迫强度的增加而降低，并且观察到海拔高度起源之间的明显差异。在这两个物种中，中低海拔种子表现出最低的性能，但与高海拔种子相比，其抗逆性略高。但是这些响应的性质是特定于物种的。我们的结果表明，发芽对热胁迫和干旱的响应不同于对单独施加的每种胁迫的响应。所以，要了解气候变化与火灾事件的相互作用如何影响发芽时间和山树的成功，就需要考虑多种胁迫因素对种子生理的影响。我们的研究结果还突出了潜在的针对特定种群和特定物种的应对措施，可用作正在进行的恢复计划的指南。