Data from: Fire and summer temperatures interact to shape seed dormancy thresholds

Data for the following paper: Zomer M, Moreira B, Pausas JG. Fire and summer temperatures interact to shape seed dormancy thresholds. Annals of Botany <br><br>It includes 3 files in ASCII format: readme file, and two data files.<br>Abstract<br>In Mediterranean ecosystems, the heat shock of wildfire disrupts physical seed dormancy in many plant species. This triggers germination in the post-fire environment where seedling establishment is optimal due to decreased competition and increased resource availability. However, to maintain the soil seedbank until a fire occurs, the minimum heat capable of breaking seed dormancy (i.e., the lower heat threshold) must be above the maximum temperatures typically observed in the soil during the summer. We therefore hypothesized that summer temperatures have shaped heat requirements for physical dormancy release. Specifically, we predicted that seeds from populations growing under warmer summers will have higher values of the lower heat threshold.To evaluate this prediction, we collected seeds from two Cistus species in 31 populations (20 Cistus albidus; 11 Cistus salviifolius) along a climate gradient of summer temperatures on the eastern coast of Spain. For each population, seeds were treated to 10-minute heat shocks, from 30°C to 120°C in 5-degree increments (19 treatments), to simulate increasing heat doses from summer to fire-related temperatures. Seeds were then germinated in the lab. For all populations, maximum germination was observed when applying temperatures associated with fire. Lower heat thresholds varied among-populations, with a positive relation between summer temperatures at seed population origin and the heat dose required to break dormancy. Our results suggest that fire drives maximum dormancy release for successful post-fire germination, while summer temperatures determine lower heat thresholds for ensuring inter-fire seed bank persistence. Significant among-population variation of thresholds also suggests that post-fire seeder species have some potential to modify their dormancy-breaking requirements in response to changing climate.<br>

本数据集配套论文如下：Zomer M、Moreira B、Pausas JG所著《火与夏季温度协同调控种子休眠阈值》，发表于《植物学年鉴（Annals of Botany）》。

本数据集包含3个ASCII格式文件：1个说明文档（readme file）与2个数据文件。

### 摘要
在地中海生态系统中，野火的热激（heat shock）会打破多数植物的物理性种子休眠（physical seed dormancy）。这会促使种子在火后环境中萌发——此时因竞争减弱、资源可获得性提升，幼苗定植条件最为适宜。

但为了在野火发生前维持土壤种子库（soil seedbank），能够打破种子休眠的最低热剂量（即热阈值下限（lower heat threshold））必须高于夏季土壤中通常观测到的最高温度。据此我们提出假说：夏季温度塑造了物理休眠解除所需的热需求。具体而言，我们预测生长于夏季更温暖环境的种群，其种子的热阈值下限值更高。

为验证该预测，我们沿西班牙东海岸的夏季温度气候梯度，从31个种群中采集了两种岩蔷薇属（Cistus）植物的种子：20个为白叶岩蔷薇（Cistus albidus）种群，11个为香线叶岩蔷薇（Cistus salviifolius）种群。针对每个种群，我们将种子置于以5℃为梯度增量、覆盖30℃至120℃区间的19组热激处理中，每组处理时长10分钟，以此模拟从夏季温度到野火相关温度的递增热剂量。随后在实验室中对种子进行萌发实验。

所有种群均在野火相关温度处理下达到最大萌发率。种群间的热阈值下限存在差异，且种子来源种群的夏季温度与打破休眠所需的热剂量呈正相关关系。

本研究结果表明，野火可促使种子最大限度解除休眠，以保障火后成功萌发；而夏季温度则决定了热阈值下限，以确保火间期种子库的存续。阈值在种群间存在显著差异，这也提示火后实生更新物种（post-fire seeder）具备一定潜力，可响应气候变化调整其休眠解除所需的热需求条件。