Grinnell College, Grinnell, IA, USA.
Donald Danforth Plant Science Center, Olivette, MO, USA.
Am J Bot. 2024 Oct;111(10):e16412. doi: 10.1002/ajb2.16412. Epub 2024 Sep 27.
Seed germination involves risk; post-germination conditions might not allow survival and reproduction. Variable, stressful environments favor seeds with germination that avoids risk (e.g., germination in conditions predicting success), spreads risk (e.g., dormancy), or escapes risk (e.g., rapid germination). Germination studies often investigate trait correlations with climate features linked to variation in post-germination reproductive success. Rarely are long-term records of population reproductive success available.
Supported by demographic and climate monitoring, we analyzed germination in the California winter-annual Clarkia xantiana subsp. xantiana. Sowing seeds of 10 populations across controlled levels of water potential and temperature, we estimated temperature-specific base water potential for 20% germination, germination time weighted by water potential above base (hydrotime), and a dormancy index (frequency of viable, ungerminated seeds). Mixed-effects models analyzed responses to (1) temperature, (2) discrete variation in reproductive success (presence or absence of years with zero seed production by a population), and (3) climate covariates, mean winter precipitation and coefficient of variation (CV) of spring precipitation. For six populations, records enabled analysis with a continuous metric of variable reproduction, the CV of per-capita reproductive success.
Populations with more variable reproductive success had higher base water potential and dormancy. Higher base water potential and faster germination occurred at warmer experimental temperatures and in seeds of populations with wetter winters.
Geographic variation in seed germination in this species suggests local adaptation to demographic risk and rainfall. High base water potential and dormancy may concentrate germination in years likely to allow reproduction, while spreading risk among years.
种子萌发涉及风险；萌发后的条件可能不允许生存和繁殖。多变、有压力的环境有利于避免风险的种子萌发（例如，在预测成功的条件下萌发）、分散风险（例如，休眠）或逃避风险（例如，快速萌发）。萌发研究通常调查与预测萌发后繁殖成功变化相关的气候特征的性状相关性。可用的种群繁殖成功率的长期记录很少。
在人口和气候监测的支持下，我们分析了加利福尼亚冬季一年生拟南芥亚种 xantiana 的萌发情况。在受控的水势和温度水平下播种了 10 个种群的种子，我们估计了 20%萌发时的特定温度基础水势、高于基础水势的水势加权萌发时间（水时）和休眠指数（有活力、未萌发种子的频率）。混合效应模型分析了对（1）温度、（2）繁殖成功率的离散变化（一个种群是否有零种子产量的年份）和（3）气候协变量（冬季平均降水和春季降水的变异系数）的响应。对于六个种群，记录允许使用可变繁殖的连续指标进行分析，即每个个体繁殖成功率的变异系数。
繁殖成功率变化较大的种群具有较高的基础水势和休眠性。在较暖的实验温度下和冬季降雨较多的种群中，基础水势较高，萌发较快。
该物种种子萌发的地理变异表明对人口风险和降雨的局部适应。高基础水势和休眠性可能会集中在有利于繁殖的年份进行萌发，同时在各年份之间分散风险。
