Drylands are predicted to become more arid and saline due to increasing global temperature and drought. Although species from the Caatinga, a Brazilian tropical dry forest, are tolerant to these conditions, the capacity for germination to withstand extreme soil temperature and water deficit associated with climate change remains to be quantified. We aimed to evaluate how germination will be affected under future climate change scenarios of limited water and increased temperature. Seeds of three species were germinated at different temperatures and osmotic potentials. Thermal time and hydrotime model parameters were established and thresholds for germination calculated. Germination performance in 2055 was predicted, by combining temperature and osmotic/salt stress thresholds, considering soil temperature and moisture following rainfall events. The most pessimistic climate scenario predicts an increase of 3.9 °C in soil temperature and 30% decrease in rainfall. Under this scenario, soil temperature is never lower than the minimum and seldomly higher than maximum temperature thresholds for germination. As long as the soil moisture (0.139 cm3 cm3) requirements are met, germination can be achieved in 1 day. According to the base water potential and soil characteristics, the minimum weekly rainfall for germination is estimated to be 17.5 mm. Currently, the required minimum rainfall occurs in 14 weeks of the year but will be reduced to 4 weeks by 2055. This may not be sufficient for seedling recruitment of some species in the natural environment. Thus, in future climate scenarios, rainfall rather than temperature will be extremely limiting for seed germination.

中文翻译：

---

降雨而非土壤温度将限制气候变化导致的干燥森林物种的种子发芽。

由于全球气温升高和干旱加剧，预计旱地将变得更加干旱和盐碱化。尽管来自巴西热带干旱森林Caatinga的物种能够耐受这些条件，但其发芽承受极端土壤温度和与气候变化相关的水分缺乏的能力仍有待量化。我们旨在评估在水和温度升高的未来气候变化情景下，发芽将如何受到影响。三种物种的种子在不同的温度和渗透势下发芽。建立了热时间和水文时间模型参数，并计算了发芽阈值。通过结合温度和渗透/盐胁迫阈值，并考虑降雨后的土壤温度和湿度，可以预测2055年的发芽性能。最悲观的气候情景预测，土壤温度将升高3.9°C，降雨量将下降30％。在这种情况下，土壤温度绝不会低于发芽的最低温度阈值，也很少高于最高温度阈值。只要满足土壤水分（0.139 cm3 cm3）的要求，发芽就可以在1天之内完成。根据基础水势和土壤特征，估计每周发芽的最低降雨量为17.5 mm。当前，所需的最小降雨发生在一年的14周，但到2055年将降至4周。这可能不足以在自然环境中招募某些物种的幼苗。因此，在未来的气候情景中，降雨而不是温度将极大地限制种子发芽。